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x264源代码简单分析：编码器主干部分-2

2016-08-06 00:00 495 查看

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H.264源代码分析文章列表：

【编码 - x264】

x264源代码简单分析：概述

x264源代码简单分析：x264命令行工具（x264.exe）

x264源代码简单分析：编码器主干部分-1

x264源代码简单分析：编码器主干部分-2

x264源代码简单分析：x264_slice_write()

x264源代码简单分析：滤波（Filter）部分

x264源代码简单分析：宏块分析（Analysis）部分-帧内宏块（Intra）

x264源代码简单分析：宏块分析（Analysis）部分-帧间宏块（Inter）

x264源代码简单分析：宏块编码（Encode）部分

x264源代码简单分析：熵编码（Entropy Encoding）部分

FFmpeg与libx264接口源代码简单分析

【解码 - libavcodec H.264 解码器】

FFmpeg的H.264解码器源代码简单分析：概述

FFmpeg的H.264解码器源代码简单分析：解析器（Parser）部分

FFmpeg的H.264解码器源代码简单分析：解码器主干部分

FFmpeg的H.264解码器源代码简单分析：熵解码（EntropyDecoding）部分

FFmpeg的H.264解码器源代码简单分析：宏块解码（Decode）部分-帧内宏块（Intra）

FFmpeg的H.264解码器源代码简单分析：宏块解码（Decode）部分-帧间宏块（Inter）

FFmpeg的H.264解码器源代码简单分析：环路滤波（Loop Filter）部分

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本文继续记录x264编码器主干部分的源代码。上一篇文章记录x264_encoder_open()，x264_encoder_headers()，和x264_encoder_close()这三个函数，本文记录x264_encoder_encode()函数。

函数调用关系图

X264编码器主干部分的源代码在整个x264中的位置如下图所示。

单击查看更清晰的图片

X264编码器主干部分的函数调用关系如下图所示。

单击查看更清晰的图片

从图中可以看出，x264主干部分最复杂的函数就是x264_encoder_encode()，该函数完成了编码一帧YUV为H.264码流的工作。与之配合的还有打开编码器的函数x264_encoder_open()，关闭编码器的函数x264_encoder_close()，以及输出SPS/PPS/SEI这样的头信息的x264_encoder_headers()。

x264_encoder_open()用于打开编码器，其中初始化了libx264编码所需要的各种变量。它调用了下面的函数：

x264_validate_parameters()：检查输入参数（例如输入图像的宽高是否为正数）。

x264_predict_16x16_init()：初始化Intra16x16帧内预测汇编函数。

x264_predict_4x4_init()：初始化Intra4x4帧内预测汇编函数。

x264_pixel_init()：初始化像素值计算相关的汇编函数（包括SAD、SATD、SSD等）。

x264_dct_init()：初始化DCT变换和DCT反变换相关的汇编函数。

x264_mc_init()：初始化运动补偿相关的汇编函数。

x264_quant_init()：初始化量化和反量化相关的汇编函数。

x264_deblock_init()：初始化去块效应滤波器相关的汇编函数。

x264_lookahead_init()：初始化Lookahead相关的变量。
x264_ratecontrol_new()：初始化码率控制相关的变量。

x264_encoder_headers()输出SPS/PPS/SEI这些H.264码流的头信息。它调用了下面的函数：

x264_sps_write()：输出SPS

x264_pps_write()：输出PPS

x264_sei_version_write()：输出SEI

x264_encoder_encode()编码一帧YUV为H.264码流。它调用了下面的函数：

x264_frame_pop_unused()：获取1个x264_frame_t类型结构体fenc。如果frames.unused[]队列不为空，就调用x264_frame_pop()从unused[]队列取1个现成的；否则就调用x264_frame_new()创建一个新的。

x264_frame_copy_picture()：将输入的图像数据拷贝至fenc。

x264_lookahead_put_frame()：将fenc放入lookahead.next.list[]队列，等待确定帧类型。

x264_lookahead_get_frames()：通过lookahead分析帧类型。该函数调用了x264_slicetype_decide()，x264_slicetype_analyse()和x264_slicetype_frame_cost()等函数。经过一些列分析之后，最终确定了帧类型信息，并且将帧放入frames.current[]队列。

x264_frame_shift()：从frames.current[]队列取出1帧用于编码。

x264_reference_update()：更新参考帧队列。

x264_reference_reset()：如果为IDR帧，调用该函数清空参考帧列表。

x264_reference_hierarchy_reset()：如果是非IDR的I帧、P帧、B帧（可做为参考帧），调用该函数。

x264_reference_build_list()：创建参考帧列表list0和list1。

x264_ratecontrol_start()：开启码率控制。

x264_slice_init()：创建 Slice Header。

x264_slices_write()：编码数据（最关键的步骤）。其中调用了x264_slice_write()完成了编码的工作（注意“x264_slices_write()”和“x264_slice_write()”名字差了一个“s”）。

x264_encoder_frame_end()：编码结束后做一些后续处理，例如记录一些统计信息。其中调用了x264_encoder_encapsulate_nals()封装NALU（添加起始码），调用x264_frame_push_unused()将fenc重新放回frames.unused[]队列，并且调用x264_ratecontrol_end()结束码率控制。

x264_encoder_close()用于关闭解码器，其中释放了libx264初始化的时候使用的各种变量。它调用了下面的函数：

x264_lookahead_delete()：释放Lookahead相关的变量。

x264_ratecontrol_summary()：汇总码率控制信息。

x264_ratecontrol_delete()：关闭码率控制。

上一篇文章已经记录了x264_encoder_open()，x264_encoder_headers()，和x264_encoder_close()这三个函数的源代码。本文继续上一篇文章的内容，记录x264_encoder_encode()函数的源代码。

x264_encoder_encode()

x264_encoder_encode()是libx264的API函数，用于编码一帧YUV为H.264码流。该函数的声明如下所示。

/* x264_encoder_encode:
*      encode one picture.
*      *pi_nal is the number of NAL units outputted in pp_nal.
*      returns the number of bytes in the returned NALs.
*      returns negative on error and zero if no NAL units returned.
*      the payloads of all output NALs are guaranteed to be sequential in memory. */
int     x264_encoder_encode( x264_t *, x264_nal_t **pp_nal, int *pi_nal, x264_picture_t *pic_in, x264_picture_t *pic_out );

x264_encoder_encode()的定义如下所示。

/****************************************************************************
* x264_encoder_encode:
*  XXX: i_poc   : is the poc of the current given picture
*       i_frame : is the number of the frame being coded
*  ex:  type frame poc
*       I      0   2*0
*       P      1   2*3
*       B      2   2*1
*       B      3   2*2
*       P      4   2*6
*       B      5   2*4
*       B      6   2*5
*
* 注释和处理：雷霄骅
* http://blog.csdn.net/leixiaohua1020 * leixiaohua1020@126.com
****************************************************************************/
//编码一帧数据
int     x264_encoder_encode( x264_t *h,
x264_nal_t **pp_nal, int *pi_nal,
x264_picture_t *pic_in,
x264_picture_t *pic_out )
{
x264_t *thread_current, *thread_prev, *thread_oldest;
int i_nal_type, i_nal_ref_idc, i_global_qp;
int overhead = NALU_OVERHEAD;

#if HAVE_OPENCL
if( h->opencl.b_fatal_error )
return -1;
#endif

if( h->i_thread_frames > 1 )
{
thread_prev    = h->thread[ h->i_thread_phase ];
h->i_thread_phase = (h->i_thread_phase + 1) % h->i_thread_frames;
thread_current = h->thread[ h->i_thread_phase ];
thread_oldest  = h->thread[ (h->i_thread_phase + 1) % h->i_thread_frames ];
x264_thread_sync_context( thread_current, thread_prev );
x264_thread_sync_ratecontrol( thread_current, thread_prev, thread_oldest );
h = thread_current;
}
else
{
thread_current =
thread_oldest  = h;
}
h->i_cpb_delay_pir_offset = h->i_cpb_delay_pir_offset_next;

/* no data out */
*pi_nal = 0;
*pp_nal = NULL;

/* ------------------- Setup new frame from picture -------------------- */
if( pic_in != NULL )
{
/* 1: Copy the picture to a frame and move it to a buffer */
//步骤1
//fenc存储了编码帧
//获取一帧的空间fenc，用来存放待编码的帧
x264_frame_t *fenc = x264_frame_pop_unused( h, 0 );
if( !fenc )
return -1;

//外部像素数据传递到内部系统
//pic_in（外部结构体x264_picture_t）到fenc（内部结构体x264_frame_t）
if( x264_frame_copy_picture( h, fenc, pic_in ) < 0 )
return -1;
//宽和高都确保是16的整数倍（宏块宽度的整数倍）
if( h->param.i_width != 16 * h->mb.i_mb_width ||
h->param.i_height != 16 * h->mb.i_mb_height )
x264_frame_expand_border_mod16( h, fenc );//扩展至16整数倍

fenc->i_frame = h->frames.i_input++;

if( fenc->i_frame == 0 )
h->frames.i_first_pts = fenc->i_pts;
if( h->frames.i_bframe_delay && fenc->i_frame == h->frames.i_bframe_delay )
h->frames.i_bframe_delay_time = fenc->i_pts - h->frames.i_first_pts;

if( h->param.b_vfr_input && fenc->i_pts <= h->frames.i_largest_pts )
x264_log( h, X264_LOG_WARNING, "non-strictly-monotonic PTS\n" );

h->frames.i_second_largest_pts = h->frames.i_largest_pts;
h->frames.i_largest_pts = fenc->i_pts;

if( (fenc->i_pic_struct < PIC_STRUCT_AUTO) || (fenc->i_pic_struct > PIC_STRUCT_TRIPLE) )
fenc->i_pic_struct = PIC_STRUCT_AUTO;

if( fenc->i_pic_struct == PIC_STRUCT_AUTO )
{
#if HAVE_INTERLACED
int b_interlaced = fenc->param ? fenc->param->b_interlaced : h->param.b_interlaced;
#else
int b_interlaced = 0;
#endif
if( b_interlaced )
{
int b_tff = fenc->param ? fenc->param->b_tff : h->param.b_tff;
fenc->i_pic_struct = b_tff ? PIC_STRUCT_TOP_BOTTOM : PIC_STRUCT_BOTTOM_TOP;
}
else
fenc->i_pic_struct = PIC_STRUCT_PROGRESSIVE;
}

if( h->param.rc.b_mb_tree && h->param.rc.b_stat_read )
{
if( x264_macroblock_tree_read( h, fenc, pic_in->prop.quant_offsets ) )
return -1;
}
else
x264_stack_align( x264_adaptive_quant_frame, h, fenc, pic_in->prop.quant_offsets );

if( pic_in->prop.quant_offsets_free )
pic_in->prop.quant_offsets_free( pic_in->prop.quant_offsets );
//降低分辨率处理（原来的一半），线性内插
//注意这里并不是6抽头滤波器的半像素内插
if( h->frames.b_have_lowres )
x264_frame_init_lowres( h, fenc );

/* 2: Place the frame into the queue for its slice type decision */
//步骤2
//fenc放入lookahead.next.list[]队列，等待确定帧类型
x264_lookahead_put_frame( h, fenc );

if( h->frames.i_input <= h->frames.i_delay + 1 - h->i_thread_frames )
{
/* Nothing yet to encode, waiting for filling of buffers */
pic_out->i_type = X264_TYPE_AUTO;
return 0;
}
}
else
{
//输入数据为空的时候（Flush Encoder？），不需要lookahead

/* signal kills for lookahead thread */
x264_pthread_mutex_lock( &h->lookahead->ifbuf.mutex );
h->lookahead->b_exit_thread = 1;
x264_pthread_cond_broadcast( &h->lookahead->ifbuf.cv_fill );
x264_pthread_mutex_unlock( &h->lookahead->ifbuf.mutex );
}

h->i_frame++;
/* 3: The picture is analyzed in the lookahead */
// 步骤3
//通过lookahead分析帧类型
if( !h->frames.current[0] )
x264_lookahead_get_frames( h );

if( !h->frames.current[0] && x264_lookahead_is_empty( h ) )
return x264_encoder_frame_end( thread_oldest, thread_current, pp_nal, pi_nal, pic_out );

/* ------------------- Get frame to be encoded ------------------------- */
/* 4: get picture to encode */
//从frames.current[]队列取出1帧[0]用于编码
h->fenc = x264_frame_shift( h->frames.current );

/* If applicable, wait for previous frame reconstruction to finish */
if( h->param.b_sliced_threads )
if( x264_threadpool_wait_all( h ) < 0 )
return -1;

if( h->i_frame == h->i_thread_frames - 1 )
h->i_reordered_pts_delay = h->fenc->i_reordered_pts;
if( h->reconfig )
{
x264_encoder_reconfig_apply( h, &h->reconfig_h->param );
h->reconfig = 0;
}
if( h->fenc->param )
{
x264_encoder_reconfig_apply( h, h->fenc->param );
if( h->fenc->param->param_free )
{
h->fenc->param->param_free( h->fenc->param );
h->fenc->param = NULL;
}
}

// ok to call this before encoding any frames, since the initial values of fdec have b_kept_as_ref=0
//更新参考帧队列frames.reference[].若为B帧则不更新
//重建帧fdec移植参考帧列表，新建一个fdec
if( x264_reference_update( h ) )
return -1;
h->fdec->i_lines_completed = -1;

if( !IS_X264_TYPE_I( h->fenc->i_type ) )
{
int valid_refs_left = 0;
for( int i = 0; h->frames.reference[i]; i++ )
if( !h->frames.reference[i]->b_corrupt )
valid_refs_left++;
/* No valid reference frames left: force an IDR. */
if( !valid_refs_left )
{
h->fenc->b_keyframe = 1;
h->fenc->i_type = X264_TYPE_IDR;
}
}

if( h->fenc->b_keyframe )
{
h->frames.i_last_keyframe = h->fenc->i_frame;
if( h->fenc->i_type == X264_TYPE_IDR )
{
h->i_frame_num = 0;
h->frames.i_last_idr = h->fenc->i_frame;
}
}
h->sh.i_mmco_command_count =
h->sh.i_mmco_remove_from_end = 0;
h->b_ref_reorder[0] =
h->b_ref_reorder[1] = 0;
h->fdec->i_poc =
h->fenc->i_poc = 2 * ( h->fenc->i_frame - X264_MAX( h->frames.i_last_idr, 0 ) );

/* ------------------- Setup frame context ----------------------------- */
/* 5: Init data dependent of frame type */
if( h->fenc->i_type == X264_TYPE_IDR )
{
//I与IDR区别
//注意IDR会导致参考帧列清空，而I不会
//I图像之后的图像可以引用I图像之间的图像做运动参考
/* reset ref pictures */
i_nal_type    = NAL_SLICE_IDR;
i_nal_ref_idc = NAL_PRIORITY_HIGHEST;
h->sh.i_type = SLICE_TYPE_I;
//若是IDR帧，则清空所有参考帧
x264_reference_reset( h );
h->frames.i_poc_last_open_gop = -1;
}
else if( h->fenc->i_type == X264_TYPE_I )
{
//I与IDR区别
//注意IDR会导致参考帧列清空，而I不会
//I图像之后的图像可以引用I图像之间的图像做运动参考
i_nal_type    = NAL_SLICE;
i_nal_ref_idc = NAL_PRIORITY_HIGH; /* Not completely true but for now it is (as all I/P are kept as ref)*/
h->sh.i_type = SLICE_TYPE_I;
x264_reference_hierarchy_reset( h );
if( h->param.b_open_gop )
h->frames.i_poc_last_open_gop = h->fenc->b_keyframe ? h->fenc->i_poc : -1;
}
else if( h->fenc->i_type == X264_TYPE_P )
{
i_nal_type    = NAL_SLICE;
i_nal_ref_idc = NAL_PRIORITY_HIGH; /* Not completely true but for now it is (as all I/P are kept as ref)*/
h->sh.i_type = SLICE_TYPE_P;
x264_reference_hierarchy_reset( h );
h->frames.i_poc_last_open_gop = -1;
}
else if( h->fenc->i_type == X264_TYPE_BREF )
{
//可以作为参考帧的B帧，这是个特色

i_nal_type    = NAL_SLICE;
i_nal_ref_idc = h->param.i_bframe_pyramid == X264_B_PYRAMID_STRICT ? NAL_PRIORITY_LOW : NAL_PRIORITY_HIGH;
h->sh.i_type = SLICE_TYPE_B;
x264_reference_hierarchy_reset( h );
}
else    /* B frame */
{
//最普通

i_nal_type    = NAL_SLICE;
i_nal_ref_idc = NAL_PRIORITY_DISPOSABLE;
h->sh.i_type = SLICE_TYPE_B;
}
//重建帧与编码帧的赋值...
h->fdec->i_type = h->fenc->i_type;
h->fdec->i_frame = h->fenc->i_frame;
h->fenc->b_kept_as_ref =
h->fdec->b_kept_as_ref = i_nal_ref_idc != NAL_PRIORITY_DISPOSABLE && h->param.i_keyint_max > 1;

h->fdec->mb_info = h->fenc->mb_info;
h->fdec->mb_info_free = h->fenc->mb_info_free;
h->fenc->mb_info = NULL;
h->fenc->mb_info_free = NULL;

h->fdec->i_pts = h->fenc->i_pts;
if( h->frames.i_bframe_delay )
{
int64_t *prev_reordered_pts = thread_current->frames.i_prev_reordered_pts;
h->fdec->i_dts = h->i_frame > h->frames.i_bframe_delay
? prev_reordered_pts[ (h->i_frame - h->frames.i_bframe_delay) % h->frames.i_bframe_delay ]
: h->fenc->i_reordered_pts - h->frames.i_bframe_delay_time;
prev_reordered_pts[ h->i_frame % h->frames.i_bframe_delay ] = h->fenc->i_reordered_pts;
}
else
h->fdec->i_dts = h->fenc->i_reordered_pts;
if( h->fenc->i_type == X264_TYPE_IDR )
h->i_last_idr_pts = h->fdec->i_pts;

/* ------------------- Init                ----------------------------- */
/* build ref list 0/1 */
//创建参考帧列表list0和list1
x264_reference_build_list( h, h->fdec->i_poc );

/* ---------------------- Write the bitstream -------------------------- */
/* Init bitstream context */
//用于输出
if( h->param.b_sliced_threads )
{
for( int i = 0; i < h->param.i_threads; i++ )
{
bs_init( &h->thread[i]->out.bs, h->thread[i]->out.p_bitstream, h->thread[i]->out.i_bitstream );
h->thread[i]->out.i_nal = 0;
}
}
else
{
bs_init( &h->out.bs, h->out.p_bitstream, h->out.i_bitstream );
h->out.i_nal = 0;
}

if( h->param.b_aud )
{
int pic_type;

if( h->sh.i_type == SLICE_TYPE_I )
pic_type = 0;
else if( h->sh.i_type == SLICE_TYPE_P )
pic_type = 1;
else if( h->sh.i_type == SLICE_TYPE_B )
pic_type = 2;
else
pic_type = 7;

x264_nal_start( h, NAL_AUD, NAL_PRIORITY_DISPOSABLE );
bs_write( &h->out.bs, 3, pic_type );
bs_rbsp_trailing( &h->out.bs );
if( x264_nal_end( h ) )
return -1;
overhead += h->out.nal[h->out.i_nal-1].i_payload + NALU_OVERHEAD;
}

h->i_nal_type = i_nal_type;
h->i_nal_ref_idc = i_nal_ref_idc;

if( h->param.b_intra_refresh )
{
if( IS_X264_TYPE_I( h->fenc->i_type ) )
{
h->fdec->i_frames_since_pir = 0;
h->b_queued_intra_refresh = 0;
/* PIR is currently only supported with ref == 1, so any intra frame effectively refreshes
* the whole frame and counts as an intra refresh. */
h->fdec->f_pir_position = h->mb.i_mb_width;
}
else if( h->fenc->i_type == X264_TYPE_P )
{
int pocdiff = (h->fdec->i_poc - h->fref[0][0]->i_poc)/2;
float increment = X264_MAX( ((float)h->mb.i_mb_width-1) / h->param.i_keyint_max, 1 );
h->fdec->f_pir_position = h->fref[0][0]->f_pir_position;
h->fdec->i_frames_since_pir = h->fref[0][0]->i_frames_since_pir + pocdiff;
if( h->fdec->i_frames_since_pir >= h->param.i_keyint_max ||
(h->b_queued_intra_refresh && h->fdec->f_pir_position + 0.5 >= h->mb.i_mb_width) )
{
h->fdec->f_pir_position = 0;
h->fdec->i_frames_since_pir = 0;
h->b_queued_intra_refresh = 0;
h->fenc->b_keyframe = 1;
}
h->fdec->i_pir_start_col = h->fdec->f_pir_position+0.5;
h->fdec->f_pir_position += increment * pocdiff;
h->fdec->i_pir_end_col = h->fdec->f_pir_position+0.5;
/* If our intra refresh has reached the right side of the frame, we're done. */
if( h->fdec->i_pir_end_col >= h->mb.i_mb_width - 1 )
{
h->fdec->f_pir_position = h->mb.i_mb_width;
h->fdec->i_pir_end_col = h->mb.i_mb_width - 1;
}
}
}

if( h->fenc->b_keyframe )
{
//每个关键帧前面重复加上SPS和PPS
/* Write SPS and PPS */
if( h->param.b_repeat_headers )
{
/* generate sequence parameters */
x264_nal_start( h, NAL_SPS, NAL_PRIORITY_HIGHEST );
x264_sps_write( &h->out.bs, h->sps );
if( x264_nal_end( h ) )
return -1;
/* Pad AUD/SPS to 256 bytes like Panasonic */
if( h->param.i_avcintra_class )
h->out.nal[h->out.i_nal-1].i_padding = 256 - bs_pos( &h->out.bs ) / 8 - 2*NALU_OVERHEAD;
overhead += h->out.nal[h->out.i_nal-1].i_payload + h->out.nal[h->out.i_nal-1].i_padding + NALU_OVERHEAD;

/* generate picture parameters */
x264_nal_start( h, NAL_PPS, NAL_PRIORITY_HIGHEST );
x264_pps_write( &h->out.bs, h->sps, h->pps );
if( x264_nal_end( h ) )
return -1;
if( h->param.i_avcintra_class )
h->out.nal[h->out.i_nal-1].i_padding = 256 - h->out.nal[h->out.i_nal-1].i_payload - NALU_OVERHEAD;
overhead += h->out.nal[h->out.i_nal-1].i_payload + h->out.nal[h->out.i_nal-1].i_padding + NALU_OVERHEAD;
}

/* when frame threading is used, buffering period sei is written in x264_encoder_frame_end */
if( h->i_thread_frames == 1 && h->sps->vui.b_nal_hrd_parameters_present )
{
x264_hrd_fullness( h );
x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE );
x264_sei_buffering_period_write( h, &h->out.bs );
if( x264_nal_end( h ) )
return -1;
overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD;
}
}

/* write extra sei */
//下面很大一段代码用于写入SEI（一部分是为了适配其他的解码器）==========================================
for( int i = 0; i < h->fenc->extra_sei.num_payloads; i++ )
{
x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE );
x264_sei_write( &h->out.bs, h->fenc->extra_sei.payloads[i].payload, h->fenc->extra_sei.payloads[i].payload_size,
h->fenc->extra_sei.payloads[i].payload_type );
if( x264_nal_end( h ) )
return -1;
overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD;
if( h->fenc->extra_sei.sei_free )
{
h->fenc->extra_sei.sei_free( h->fenc->extra_sei.payloads[i].payload );
h->fenc->extra_sei.payloads[i].payload = NULL;
}
}

if( h->fenc->extra_sei.sei_free )
{
h->fenc->extra_sei.sei_free( h->fenc->extra_sei.payloads );
h->fenc->extra_sei.payloads = NULL;
h->fenc->extra_sei.sei_free = NULL;
}
//特殊的SEI信息（Avid等解码器需要）
if( h->fenc->b_keyframe )
{
/* Avid's decoder strictly wants two SEIs for AVC-Intra so we can't insert the x264 SEI */
if( h->param.b_repeat_headers && h->fenc->i_frame == 0 && !h->param.i_avcintra_class )
{
/* identify ourself */
x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE );
if( x264_sei_version_write( h, &h->out.bs ) )
return -1;
if( x264_nal_end( h ) )
return -1;
overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD;
}

if( h->fenc->i_type != X264_TYPE_IDR )
{
int time_to_recovery = h->param.b_open_gop ? 0 : X264_MIN( h->mb.i_mb_width - 1, h->param.i_keyint_max ) + h->param.i_bframe - 1;
x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE );
x264_sei_recovery_point_write( h, &h->out.bs, time_to_recovery );
if( x264_nal_end( h ) )
return -1;
overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD;
}
}

if( h->param.i_frame_packing >= 0 && (h->fenc->b_keyframe || h->param.i_frame_packing == 5) )
{
x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE );
x264_sei_frame_packing_write( h, &h->out.bs );
if( x264_nal_end( h ) )
return -1;
overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD;
}

/* generate sei pic timing */
if( h->sps->vui.b_pic_struct_present || h->sps->vui.b_nal_hrd_parameters_present )
{
x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE );
x264_sei_pic_timing_write( h, &h->out.bs );
if( x264_nal_end( h ) )
return -1;
overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD;
}

/* As required by Blu-ray. */
if( !IS_X264_TYPE_B( h->fenc->i_type ) && h->b_sh_backup )
{
h->b_sh_backup = 0;
x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE );
x264_sei_dec_ref_pic_marking_write( h, &h->out.bs );
if( x264_nal_end( h ) )
return -1;
overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD;
}

if( h->fenc->b_keyframe && h->param.b_intra_refresh )
h->i_cpb_delay_pir_offset_next = h->fenc->i_cpb_delay;

/* Filler space: 10 or 18 SEIs' worth of space, depending on resolution */
if( h->param.i_avcintra_class )
{
/* Write an empty filler NAL to mimic the AUD in the P2 format*/
x264_nal_start( h, NAL_FILLER, NAL_PRIORITY_DISPOSABLE );
x264_filler_write( h, &h->out.bs, 0 );
if( x264_nal_end( h ) )
return -1;
overhead += h->out.nal[h->out.i_nal-1].i_payload + NALU_OVERHEAD;

/* All lengths are magic lengths that decoders expect to see */
/* "UMID" SEI */
x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE );
if( x264_sei_avcintra_umid_write( h, &h->out.bs ) < 0 )
return -1;
if( x264_nal_end( h ) )
return -1;
overhead += h->out.nal[h->out.i_nal-1].i_payload + SEI_OVERHEAD;

int unpadded_len;
int total_len;
if( h->param.i_height == 1080 )
{
unpadded_len = 5780;
total_len = 17*512;
}
else
{
unpadded_len = 2900;
total_len = 9*512;
}
/* "VANC" SEI */
x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE );
if( x264_sei_avcintra_vanc_write( h, &h->out.bs, unpadded_len ) < 0 )
return -1;
if( x264_nal_end( h ) )
return -1;

h->out.nal[h->out.i_nal-1].i_padding = total_len - h->out.nal[h->out.i_nal-1].i_payload - SEI_OVERHEAD;
overhead += h->out.nal[h->out.i_nal-1].i_payload + h->out.nal[h->out.i_nal-1].i_padding + SEI_OVERHEAD;
}
//写入SEI代码结束========================================================

/* Init the rate control */
/* FIXME: Include slice header bit cost. */
//码率控制单元初始化
x264_ratecontrol_start( h, h->fenc->i_qpplus1, overhead*8 );
i_global_qp = x264_ratecontrol_qp( h );

pic_out->i_qpplus1 =
h->fdec->i_qpplus1 = i_global_qp + 1;

if( h->param.rc.b_stat_read && h->sh.i_type != SLICE_TYPE_I )
{
x264_reference_build_list_optimal( h );
x264_reference_check_reorder( h );
}

if( h->i_ref[0] )
h->fdec->i_poc_l0ref0 = h->fref[0][0]->i_poc;

/* ------------------------ Create slice header  ----------------------- */
//创建Slice Header
x264_slice_init( h, i_nal_type, i_global_qp );

/*------------------------- Weights -------------------------------------*/
//加权预测

if( h->sh.i_type == SLICE_TYPE_B )
x264_macroblock_bipred_init( h );

x264_weighted_pred_init( h );

if( i_nal_ref_idc != NAL_PRIORITY_DISPOSABLE )
h->i_frame_num++;

/* Write frame */
h->i_threadslice_start = 0;
h->i_threadslice_end = h->mb.i_mb_height;

if( h->i_thread_frames > 1 )
{
x264_threadpool_run( h->threadpool, (void*)x264_slices_write, h );
h->b_thread_active = 1;
}
else if( h->param.b_sliced_threads )
{
if( x264_threaded_slices_write( h ) )
return -1;
}
else{
//真正的编码——编码1个图像帧（注意这里“slices”后面有“s”）
if( (intptr_t)x264_slices_write( h ) )
return -1;
}
//结束的时候做一些处理，记录一些统计信息
//输出NALU
//输出重建帧
return x264_encoder_frame_end( thread_oldest, thread_current, pp_nal, pi_nal, pic_out );
}

从源代码可以看出，x264_encoder_encode()的流程大致如下：

（1）调用x264_frame_pop_unused获取一个空的fenc（x264_frame_t类型）用于存储一帧编码像素数据。

（2）调用x264_frame_copy_picture()将外部结构体的pic_in（x264_picture_t类型）的数据拷贝给内部结构体的fenc（x264_frame_t类型）。

（3）调用x264_lookahead_put_frame()将fenc放入Lookahead模块的队列中，等待确定帧类型。

（4）调用x264_lookahead_get_frames()分析Lookahead模块中一个帧的帧类型。分析后的帧保存在frames.current[]中。

（5）调用x264_frame_shift()从frames.current[]中取出分析帧类型之后的fenc。

（6）调用x264_reference_update()更新参考帧队列frames.reference[]。

（7）如果编码帧fenc是IDR帧，调用x264_reference_reset()清空参考帧队列frames.reference[]。

（8）调用x264_reference_build_list()创建参考帧列表List0和List1。

（9）根据选项做一些配置：

a)如果b_aud不为0，输出AUD类型NALU

b)在当前帧是关键帧的情况下，如果b_repeat_headers不为0，调用x264_sps_write()和x264_pps_write()输出SPS和PPS。

c)输出一些特殊的SEI信息，用于适配各种解码器。
（10）调用x264_slice_init()初始化Slice Header信息。

（11）调用x264_slices_write()进行编码。该部分是libx264的核心，在后续文章中会详细分析。
（12）调用x264_encoder_frame_end()做一些编码后的后续处理。

下文将会按照步骤对上述函数进行简单的分析。

x264_frame_pop_unused()

x264_frame_pop_unused()用于获取1个x264_frame_t类型结构体fenc。该函数的定义位于common\frame.c，如下所示。

//获取一帧的编码帧fenc或者重建帧fdec
x264_frame_t *x264_frame_pop_unused( x264_t *h, int b_fdec )
{
x264_frame_t *frame;
if( h->frames.unused[b_fdec][0] )//unused队列不为空
frame = x264_frame_pop( h->frames.unused[b_fdec] );//从unused队列取
else
frame = x264_frame_new( h, b_fdec );//分配一帧空间
if( !frame )
return NULL;
frame->b_last_minigop_bframe = 0;
frame->i_reference_count = 1;
frame->b_intra_calculated = 0;
frame->b_scenecut = 1;
frame->b_keyframe = 0;
frame->b_corrupt = 0;
frame->i_slice_count = h->param.b_sliced_threads ? h->param.i_threads : 1;

memset( frame->weight, 0, sizeof(frame->weight) );
memset( frame->f_weighted_cost_delta, 0, sizeof(frame->f_weighted_cost_delta) );

return frame;
}

从源代码可以看出，如果frames.unused[]队列不为空，x264_frame_pop_unused()就调用x264_frame_pop()从unused[]队列取1个现成的；否则就调用x264_frame_new()创建一个新的。下面看一下这两个函数。

x264_frame_pop()

x264_frame_pop()用于从一个队列的尾部取出一个帧。该函数的定义位于common\frame.c，如下所示。

//从队列的尾部取出一帧
x264_frame_t *x264_frame_pop( x264_frame_t **list )
{
x264_frame_t *frame;
int i = 0;
assert( list[0] );
while( list[i+1] ) i++;
frame = list[i];
list[i] = NULL;
return frame;
}

从源代码中可以看出，x264_frame_pop()首先通过一个while()循环找到队列尾部的元素，然后将该元素作为返回值返回。

x264_frame_new()

x264_frame_new()用于新建一个x264_frame_t。该函数的定义位于common\frame.c，如下所示。

//新建一个帧
//b_fdec：取1的时候为重建帧fdec，取0的时候为编码帧fenc
static x264_frame_t *x264_frame_new( x264_t *h, int b_fdec )
{
x264_frame_t *frame;
//注意转换后只有3种colorspace：X264_CSP_NV12(对应YUV420),X264_CSP_NV16(对应YUV422),X264_CSP_I444(对应YUV444)
int i_csp = x264_frame_internal_csp( h->param.i_csp );
int i_mb_count = h->mb.i_mb_count;
int i_stride, i_width, i_lines, luma_plane_count;
int i_padv = PADV << PARAM_INTERLACED;
int align = 16;
#if ARCH_X86 || ARCH_X86_64
if( h->param.cpu&X264_CPU_CACHELINE_64 )
align = 64;
else if( h->param.cpu&X264_CPU_CACHELINE_32 || h->param.cpu&X264_CPU_AVX2 )
align = 32;
#endif
#if ARCH_PPC
int disalign = 1<<9;
#else
int disalign = 1<<10;
#endif
//给frame分配内存，并置零
CHECKED_MALLOCZERO( frame, sizeof(x264_frame_t) );
PREALLOC_INIT

/* allocate frame data (+64 for extra data for me) */
//以像素为单位的宽高
i_width  = h->mb.i_mb_width*16;
i_lines  = h->mb.i_mb_height*16;
i_stride = align_stride( i_width + 2*PADH, align, disalign );

if( i_csp == X264_CSP_NV12 || i_csp == X264_CSP_NV16 )
{
//YUV422,YUV420情况

luma_plane_count = 1;
frame->i_plane = 2;
for( int i = 0; i < 2; i++ )
{
frame->i_width[i] = i_width >> i;
frame->i_lines[i] = i_lines >> (i && i_csp == X264_CSP_NV12);
frame->i_stride[i] = i_stride;
}
}
else if( i_csp == X264_CSP_I444 )
{
//YUV444情况
luma_plane_count = 3;
frame->i_plane = 3;
for( int i = 0; i < 3; i++ )
{
frame->i_width[i] = i_width;
frame->i_lines[i] = i_lines;
frame->i_stride[i] = i_stride;
}
}
else
goto fail;
//赋值赋值赋值...
frame->i_csp = i_csp;
frame->i_width_lowres = frame->i_width[0]/2;
frame->i_lines_lowres = frame->i_lines[0]/2;
frame->i_stride_lowres = align_stride( frame->i_width_lowres + 2*PADH, align, disalign<<1 );

for( int i = 0; i < h->param.i_bframe + 2; i++ )
for( int j = 0; j < h->param.i_bframe + 2; j++ )
PREALLOC( frame->i_row_satds[i][j], i_lines/16 * sizeof(int) );

frame->i_poc = -1;
frame->i_type = X264_TYPE_AUTO;
frame->i_qpplus1 = X264_QP_AUTO;
frame->i_pts = -1;
frame->i_frame = -1;
frame->i_frame_num = -1;
frame->i_lines_completed = -1;
frame->b_fdec = b_fdec;
frame->i_pic_struct = PIC_STRUCT_AUTO;
frame->i_field_cnt = -1;
frame->i_duration =
frame->i_cpb_duration =
frame->i_dpb_output_delay =
frame->i_cpb_delay = 0;
frame->i_coded_fields_lookahead =
frame->i_cpb_delay_lookahead = -1;

frame->orig = frame;

if( i_csp == X264_CSP_NV12 || i_csp == X264_CSP_NV16 )
{
int chroma_padv = i_padv >> (i_csp == X264_CSP_NV12);
int chroma_plane_size = (frame->i_stride[1] * (frame->i_lines[1] + 2*chroma_padv));
PREALLOC( frame->buffer[1], chroma_plane_size * sizeof(pixel) );
if( PARAM_INTERLACED )
PREALLOC( frame->buffer_fld[1], chroma_plane_size * sizeof(pixel) );
}

/* all 4 luma planes allocated together, since the cacheline split code
* requires them to be in-phase wrt cacheline alignment. */

for( int p = 0; p < luma_plane_count; p++ )
{
int luma_plane_size = align_plane_size( frame->i_stride[p] * (frame->i_lines[p] + 2*i_padv), disalign );
if( h->param.analyse.i_subpel_refine && b_fdec )
{
/* FIXME: Don't allocate both buffers in non-adaptive MBAFF. */
PREALLOC( frame->buffer[p], 4*luma_plane_size * sizeof(pixel) );
if( PARAM_INTERLACED )
PREALLOC( frame->buffer_fld[p], 4*luma_plane_size * sizeof(pixel) );
}
else
{
PREALLOC( frame->buffer[p], luma_plane_size * sizeof(pixel) );
if( PARAM_INTERLACED )
PREALLOC( frame->buffer_fld[p], luma_plane_size * sizeof(pixel) );
}
}

frame->b_duplicate = 0;

if( b_fdec ) /* fdec frame */
{
//重建帧fdec
PREALLOC( frame->mb_type, i_mb_count * sizeof(int8_t) );
PREALLOC( frame->mb_partition, i_mb_count * sizeof(uint8_t) );
PREALLOC( frame->mv[0], 2*16 * i_mb_count * sizeof(int16_t) );
PREALLOC( frame->mv16x16, 2*(i_mb_count+1) * sizeof(int16_t) );
PREALLOC( frame->ref[0], 4 * i_mb_count * sizeof(int8_t) );
if( h->param.i_bframe )
{
PREALLOC( frame->mv[1], 2*16 * i_mb_count * sizeof(int16_t) );
PREALLOC( frame->ref[1], 4 * i_mb_count * sizeof(int8_t) );
}
else
{
frame->mv[1]  = NULL;
frame->ref[1] = NULL;
}
PREALLOC( frame->i_row_bits, i_lines/16 * sizeof(int) );
PREALLOC( frame->f_row_qp, i_lines/16 * sizeof(float) );
PREALLOC( frame->f_row_qscale, i_lines/16 * sizeof(float) );
if( h->param.analyse.i_me_method >= X264_ME_ESA )
PREALLOC( frame->buffer[3], frame->i_stride[0] * (frame->i_lines[0] + 2*i_padv) * sizeof(uint16_t) << h->frames.b_have_sub8x8_esa );
if( PARAM_INTERLACED )
PREALLOC( frame->field, i_mb_count * sizeof(uint8_t) );
if( h->param.analyse.b_mb_info )
PREALLOC( frame->effective_qp, i_mb_count * sizeof(uint8_t) );
}
else /* fenc frame */
{
//编码帧fenc
if( h->frames.b_have_lowres )
{
int luma_plane_size = align_plane_size( frame->i_stride_lowres * (frame->i_lines[0]/2 + 2*PADV), disalign );

PREALLOC( frame->buffer_lowres[0], 4 * luma_plane_size * sizeof(pixel) );

for( int j = 0; j <= !!h->param.i_bframe; j++ )
for( int i = 0; i <= h->param.i_bframe; i++ )
{
PREALLOC( frame->lowres_mvs[j][i], 2*h->mb.i_mb_count*sizeof(int16_t) );
PREALLOC( frame->lowres_mv_costs[j][i], h->mb.i_mb_count*sizeof(int) );
}
PREALLOC( frame->i_propagate_cost, (i_mb_count+7) * sizeof(uint16_t) );
for( int j = 0; j <= h->param.i_bframe+1; j++ )
for( int i = 0; i <= h->param.i_bframe+1; i++ )
PREALLOC( frame->lowres_costs[j][i], (i_mb_count+3) * sizeof(uint16_t) );

}
if( h->param.rc.i_aq_mode )
{
PREALLOC( frame->f_qp_offset, h->mb.i_mb_count * sizeof(float) );
PREALLOC( frame->f_qp_offset_aq, h->mb.i_mb_count * sizeof(float) );
if( h->frames.b_have_lowres )
PREALLOC( frame->i_inv_qscale_factor, (h->mb.i_mb_count+3) * sizeof(uint16_t) );
}
}

PREALLOC_END( frame->base );

if( i_csp == X264_CSP_NV12 || i_csp == X264_CSP_NV16 )
{
int chroma_padv = i_padv >> (i_csp == X264_CSP_NV12);
frame->plane[1] = frame->buffer[1] + frame->i_stride[1] * chroma_padv + PADH;
if( PARAM_INTERLACED )
frame->plane_fld[1] = frame->buffer_fld[1] + frame->i_stride[1] * chroma_padv + PADH;
}

for( int p = 0; p < luma_plane_count; p++ )
{
int luma_plane_size = align_plane_size( frame->i_stride[p] * (frame->i_lines[p] + 2*i_padv), disalign );
if( h->param.analyse.i_subpel_refine && b_fdec )
{
for( int i = 0; i < 4; i++ )
{
frame->filtered[p][i] = frame->buffer[p] + i*luma_plane_size + frame->i_stride[p] * i_padv + PADH;
frame->filtered_fld[p][i] = frame->buffer_fld[p] + i*luma_plane_size + frame->i_stride[p] * i_padv + PADH;
}
frame->plane[p] = frame->filtered[p][0];
frame->plane_fld[p] = frame->filtered_fld[p][0];
}
else
{
frame->filtered[p][0] = frame->plane[p] = frame->buffer[p] + frame->i_stride[p] * i_padv + PADH;
frame->filtered_fld[p][0] = frame->plane_fld[p] = frame->buffer_fld[p] + frame->i_stride[p] * i_padv + PADH;
}
}

if( b_fdec )
{
M32( frame->mv16x16[0] ) = 0;
frame->mv16x16++;

if( h->param.analyse.i_me_method >= X264_ME_ESA )
frame->integral = (uint16_t*)frame->buffer[3] + frame->i_stride[0] * i_padv + PADH;
}
else
{
if( h->frames.b_have_lowres )
{
int luma_plane_size = align_plane_size( frame->i_stride_lowres * (frame->i_lines[0]/2 + 2*PADV), disalign );
for( int i = 0; i < 4; i++ )
frame->lowres[i] = frame->buffer_lowres[0] + (frame->i_stride_lowres * PADV + PADH) + i * luma_plane_size;

for( int j = 0; j <= !!h->param.i_bframe; j++ )
for( int i = 0; i <= h->param.i_bframe; i++ )
memset( frame->lowres_mvs[j][i], 0, 2*h->mb.i_mb_count*sizeof(int16_t) );

frame->i_intra_cost = frame->lowres_costs[0][0];
memset( frame->i_intra_cost, -1, (i_mb_count+3) * sizeof(uint16_t) );

if( h->param.rc.i_aq_mode )
/* shouldn't really be initialized, just silences a valgrind false-positive in x264_mbtree_propagate_cost_sse2 */
memset( frame->i_inv_qscale_factor, 0, (h->mb.i_mb_count+3) * sizeof(uint16_t) );
}
}

if( x264_pthread_mutex_init( &frame->mutex, NULL ) )
goto fail;
if( x264_pthread_cond_init( &frame->cv, NULL ) )
goto fail;

#if HAVE_OPENCL
frame->opencl.ocl = h->opencl.ocl;
#endif

return frame;

fail:
x264_free( frame );
return NULL;
}

从源代码中可以看出，x264_frame_new()声明了一个frame指针，并在后续过程中对该frame的成员变量进行内存分配和注释。需要注意的是编码帧fenc和重建帧fdec初始化的变量是不一样的——函数的输入参数b_fdec不为0的时候初始化重建帧，否则初始化编码帧。在这个函数中涉及到一个简单的函数x264_frame_internal_csp()，用于把种类繁多的外部Colorspace转换为简单的内部Colorspace。

x264_frame_internal_csp()

x264_frame_internal_csp()用于把外部Colorspace转换为内部Colorspace。该函数的定义如下所示。

//注意转换后只有3种内部colorspace：X264_CSP_NV12(对应YUV420),X264_CSP_NV16(对应YUV422),X264_CSP_I444(对应YUV444)
static int x264_frame_internal_csp( int external_csp )
{
switch( external_csp & X264_CSP_MASK )
{
case X264_CSP_NV12:
case X264_CSP_I420:
case X264_CSP_YV12:
return X264_CSP_NV12;
case X264_CSP_NV16:
case X264_CSP_I422:
case X264_CSP_YV16:
case X264_CSP_V210:
return X264_CSP_NV16;
case X264_CSP_I444:
case X264_CSP_YV24:
case X264_CSP_BGR:
case X264_CSP_BGRA:
case X264_CSP_RGB:
return X264_CSP_I444;
default:
return X264_CSP_NONE;
}
}

x264_frame_copy_picture()

x264_frame_copy_picture()用于将外部结构体x264_picture_t的数据拷贝给内部结构体x264_frame_t。该函数的定义位于common\frame.c，如下所示。

//拷贝帧数据
//src（外部结构体x264_picture_t）到dst（内部结构体x264_frame_t）
int x264_frame_copy_picture( x264_t *h, x264_frame_t *dst, x264_picture_t *src )
{
int i_csp = src->img.i_csp & X264_CSP_MASK;
//注意转换后只有3种内部colorspace：X264_CSP_NV12(对应YUV420),X264_CSP_NV16(对应YUV422),X264_CSP_I444(对应YUV444)
if( dst->i_csp != x264_frame_internal_csp( i_csp ) )
{
x264_log( h, X264_LOG_ERROR, "Invalid input colorspace\n" );
return -1;
}

#if HIGH_BIT_DEPTH
if( !(src->img.i_csp & X264_CSP_HIGH_DEPTH) )
{
x264_log( h, X264_LOG_ERROR, "This build of x264 requires high depth input. Rebuild to support 8-bit input.\n" );
return -1;
}
#else
if( src->img.i_csp & X264_CSP_HIGH_DEPTH )
{
x264_log( h, X264_LOG_ERROR, "This build of x264 requires 8-bit input. Rebuild to support high depth input.\n" );
return -1;
}
#endif

if( BIT_DEPTH != 10 && i_csp == X264_CSP_V210 )
{
x264_log( h, X264_LOG_ERROR, "v210 input is only compatible with bit-depth of 10 bits\n" );
return -1;
}
//赋值赋值赋值
dst->i_type     = src->i_type;
dst->i_qpplus1  = src->i_qpplus1;
dst->i_pts      = dst->i_reordered_pts = src->i_pts;
dst->param      = src->param;
dst->i_pic_struct = src->i_pic_struct;
dst->extra_sei  = src->extra_sei;
dst->opaque     = src->opaque;
dst->mb_info    = h->param.analyse.b_mb_info ? src->prop.mb_info : NULL;
dst->mb_info_free = h->param.analyse.b_mb_info ? src->prop.mb_info_free : NULL;

uint8_t *pix[3];
int stride[3];
if( i_csp == X264_CSP_V210 )
{
stride[0] = src->img.i_stride[0];
pix[0] = src->img.plane[0];

h->mc.plane_copy_deinterleave_v210( dst->plane[0], dst->i_stride[0],
dst->plane[1], dst->i_stride[1],
(uint32_t *)pix[0], stride[0]/sizeof(uint32_t), h->param.i_width, h->param.i_height );
}
else if( i_csp >= X264_CSP_BGR )
{
stride[0] = src->img.i_stride[0];
pix[0] = src->img.plane[0];
if( src->img.i_csp & X264_CSP_VFLIP )
{
pix[0] += (h->param.i_height-1) * stride[0];
stride[0] = -stride[0];
}
int b = i_csp==X264_CSP_RGB;
h->mc.plane_copy_deinterleave_rgb( dst->plane[1+b], dst->i_stride[1+b],
dst->plane[0], dst->i_stride[0],
dst->plane[2-b], dst->i_stride[2-b],
(pixel*)pix[0], stride[0]/sizeof(pixel), i_csp==X264_CSP_BGRA ? 4 : 3, h->param.i_width, h->param.i_height );
}
else
{
int v_shift = CHROMA_V_SHIFT;
get_plane_ptr( h, src, &pix[0], &stride[0], 0, 0, 0 );
//拷贝像素
h->mc.plane_copy( dst->plane[0], dst->i_stride[0], (pixel*)pix[0],
stride[0]/sizeof(pixel), h->param.i_width, h->param.i_height );
if( i_csp == X264_CSP_NV12 || i_csp == X264_CSP_NV16 )
{
get_plane_ptr( h, src, &pix[1], &stride[1], 1, 0, v_shift );
h->mc.plane_copy( dst->plane[1], dst->i_stride[1], (pixel*)pix[1],
stride[1]/sizeof(pixel), h->param.i_width, h->param.i_height>>v_shift );
}
else if( i_csp == X264_CSP_I420 || i_csp == X264_CSP_I422 || i_csp == X264_CSP_YV12 || i_csp == X264_CSP_YV16 )
{
int uv_swap = i_csp == X264_CSP_YV12 || i_csp == X264_CSP_YV16;
get_plane_ptr( h, src, &pix[1], &stride[1], uv_swap ? 2 : 1, 1, v_shift );
get_plane_ptr( h, src, &pix[2], &stride[2], uv_swap ? 1 : 2, 1, v_shift );
h->mc.plane_copy_interleave( dst->plane[1], dst->i_stride[1],
(pixel*)pix[1], stride[1]/sizeof(pixel),
(pixel*)pix[2], stride[2]/sizeof(pixel),
h->param.i_width>>1, h->param.i_height>>v_shift );
}
else //if( i_csp == X264_CSP_I444 || i_csp == X264_CSP_YV24 )
{
get_plane_ptr( h, src, &pix[1], &stride[1], i_csp==X264_CSP_I444 ? 1 : 2, 0, 0 );
get_plane_ptr( h, src, &pix[2], &stride[2], i_csp==X264_CSP_I444 ? 2 : 1, 0, 0 );
h->mc.plane_copy( dst->plane[1], dst->i_stride[1], (pixel*)pix[1],
stride[1]/sizeof(pixel), h->param.i_width, h->param.i_height );
h->mc.plane_copy( dst->plane[2], dst->i_stride[2], (pixel*)pix[2],
stride[2]/sizeof(pixel), h->param.i_width, h->param.i_height );
}
}
return 0;
}

从源代码可以看出，x264_frame_t和x264_picture_t结构体中很多字段是一模一样的，x264_frame_copy_picture()只是简单地将x264_picture_t中字段的值赋值给了x264_frame_t。

x264_lookahead_put_frame()

x264_lookahead_put_frame()将编码帧放入Lookahead模块的队列中，等待确定帧类型。该函数的定义位于encoder\lookahead.c，如下所示。

//x264_frame_t放入x264_sync_frame_list_t队列
void x264_lookahead_put_frame( x264_t *h, x264_frame_t *frame )
{
if( h->param.i_sync_lookahead )
x264_sync_frame_list_push( &h->lookahead->ifbuf, frame );
else
x264_sync_frame_list_push( &h->lookahead->next, frame );//放入next队列
}

从源代码可以看出，i_sync_lookahead不为0的时候，会将编码帧放入lookahead.ifbuf[]中，否则会将编码帧放入lookahead.next[]中。放入帧的时候会调用x264_sync_frame_list_push()。

x264_sync_frame_list_push()

x264_sync_frame_list_push()用于向x264_sync_frame_list_t类型的队列中放入一个帧。该函数的定义位于common\frame.c，如下所示。

void x264_sync_frame_list_push( x264_sync_frame_list_t *slist, x264_frame_t *frame )
{
x264_pthread_mutex_lock( &slist->mutex );
while( slist->i_size == slist->i_max_size )
x264_pthread_cond_wait( &slist->cv_empty, &slist->mutex );
//放入
slist->list[ slist->i_size++ ] = frame;
x264_pthread_mutex_unlock( &slist->mutex );
x264_pthread_cond_broadcast( &slist->cv_fill );
}

从源代码中可以看出，x264_sync_frame_list_push()将frame放在了x264_sync_frame_list_t.list的尾部。

x264_lookahead_get_frames()

x264_lookahead_get_frames()通过lookahead模块分析帧类型。该函数的定义位于encoder\lookahead.c，如下所示。

//通过lookahead分析帧类型
void x264_lookahead_get_frames( x264_t *h )
{
if( h->param.i_sync_lookahead )
{   /* We have a lookahead thread, so get frames from there */
x264_pthread_mutex_lock( &h->lookahead->ofbuf.mutex );
while( !h->lookahead->ofbuf.i_size && h->lookahead->b_thread_active )
x264_pthread_cond_wait( &h->lookahead->ofbuf.cv_fill, &h->lookahead->ofbuf.mutex );
x264_lookahead_encoder_shift( h );
x264_pthread_mutex_unlock( &h->lookahead->ofbuf.mutex );
}
else
{   /* We are not running a lookahead thread, so perform all the slicetype decide on the fly */
//currect[]必须为空，next不能为空？
if( h->frames.current[0] || !h->lookahead->next.i_size )
return;
//分析lookahead->next->list帧的类型
x264_stack_align( x264_slicetype_decide, h );
//更新lookahead->last_nonb
x264_lookahead_update_last_nonb( h, h->lookahead->next.list[0] );
int shift_frames = h->lookahead->next.list[0]->i_bframes + 1;
//lookahead->next.list移动到lookahead->ofbuf.list
x264_lookahead_shift( &h->lookahead->ofbuf, &h->lookahead->next, shift_frames );

/* For MB-tree and VBV lookahead, we have to perform propagation analysis on I-frames too. */
if( h->lookahead->b_analyse_keyframe && IS_X264_TYPE_I( h->lookahead->last_nonb->i_type ) )
x264_stack_align( x264_slicetype_analyse, h, shift_frames );

//lookahead->ofbuf.list帧移动到frames->current
x264_lookahead_encoder_shift( h );
}
}

从源代码中可以看出，x264_lookahead_get_frames()调用了x264_slicetype_decide()用于确定帧类型。在这里需要注意，Lookahead模块的代码量比较大，暂时不做详细的分析，仅简单理一下脉络。

x264_slicetype_decide()

x264_slicetype_decide()用于确定帧类型，该函数的定义位于encoder\slicetype.c，如下所示。

//确定帧的类型（I、B、P）
void x264_slicetype_decide( x264_t *h )
{
x264_frame_t *frames[X264_BFRAME_MAX+2];
x264_frame_t *frm;
int bframes;
int brefs;

if( !h->lookahead->next.i_size )
return;

int lookahead_size = h->lookahead->next.i_size;

//遍历next队列
for( int i = 0; i < h->lookahead->next.i_size; i++ )
{
if( h->param.b_vfr_input )
{
if( lookahead_size-- > 1 )
h->lookahead->next.list[i]->i_duration = 2 * (h->lookahead->next.list[i+1]->i_pts - h->lookahead->next.list[i]->i_pts);
else
h->lookahead->next.list[i]->i_duration = h->i_prev_duration;
}
else
h->lookahead->next.list[i]->i_duration = delta_tfi_divisor[h->lookahead->next.list[i]->i_pic_struct];
h->i_prev_duration = h->lookahead->next.list[i]->i_duration;
h->lookahead->next.list[i]->f_duration = (double)h->lookahead->next.list[i]->i_duration
* h->sps->vui.i_num_units_in_tick
/ h->sps->vui.i_time_scale;

if( h->lookahead->next.list[i]->i_frame > h->i_disp_fields_last_frame && lookahead_size > 0 )
{
h->lookahead->next.list[i]->i_field_cnt = h->i_disp_fields;
h->i_disp_fields += h->lookahead->next.list[i]->i_duration;
h->i_disp_fields_last_frame = h->lookahead->next.list[i]->i_frame;
}
else if( lookahead_size == 0 )
{
h->lookahead->next.list[i]->i_field_cnt = h->i_disp_fields;
h->lookahead->next.list[i]->i_duration = h->i_prev_duration;
}
}

if( h->param.rc.b_stat_read )
{
//b_stat_read在2pass模式的第2遍才不为0

/* Use the frame types from the first pass */
for( int i = 0; i < h->lookahead->next.i_size; i++ )
h->lookahead->next.list[i]->i_type =
x264_ratecontrol_slice_type( h, h->lookahead->next.list[i]->i_frame );
}
else if( (h->param.i_bframe && h->param.i_bframe_adaptive)
|| h->param.i_scenecut_threshold
|| h->param.rc.b_mb_tree
|| (h->param.rc.i_vbv_buffer_size && h->param.rc.i_lookahead) )
x264_slicetype_analyse( h, 0 );//分析帧的类型（I、B、P）
//===========================================================================

for( bframes = 0, brefs = 0;; bframes++ )
{
//从next队列取出1个
frm = h->lookahead->next.list[bframes];
//BREF的处理
if( frm->i_type == X264_TYPE_BREF && h->param.i_bframe_pyramid < X264_B_PYRAMID_NORMAL &&
brefs == h->param.i_bframe_pyramid )
{
//BREF改成B
frm->i_type = X264_TYPE_B;
x264_log( h, X264_LOG_WARNING, "B-ref at frame %d incompatible with B-pyramid %s \n",
frm->i_frame, x264_b_pyramid_names[h->param.i_bframe_pyramid] );
}
/* pyramid with multiple B-refs needs a big enough dpb that the preceding P-frame stays available.
smaller dpb could be supported by smart enough use of mmco, but it's easier just to forbid it. */
else if( frm->i_type == X264_TYPE_BREF && h->param.i_bframe_pyramid == X264_B_PYRAMID_NORMAL &&
brefs && h->param.i_frame_reference <= (brefs+3) )
{
frm->i_type = X264_TYPE_B;
x264_log( h, X264_LOG_WARNING, "B-ref at frame %d incompatible with B-pyramid %s and %d reference frames\n",
frm->i_frame, x264_b_pyramid_names[h->param.i_bframe_pyramid], h->param.i_frame_reference );
}
//Keyframe处理
if( frm->i_type == X264_TYPE_KEYFRAME )
frm->i_type = h->param.b_open_gop ? X264_TYPE_I : X264_TYPE_IDR;

/* Limit GOP size */
if( (!h->param.b_intra_refresh || frm->i_frame == 0) && frm->i_frame - h->lookahead->i_last_keyframe >= h->param.i_keyint_max )
{
if( frm->i_type == X264_TYPE_AUTO || frm->i_type == X264_TYPE_I )
frm->i_type = h->param.b_open_gop && h->lookahead->i_last_keyframe >= 0 ? X264_TYPE_I : X264_TYPE_IDR;
int warn = frm->i_type != X264_TYPE_IDR;
if( warn && h->param.b_open_gop )
warn &= frm->i_type != X264_TYPE_I;
if( warn )
{
x264_log( h, X264_LOG_WARNING, "specified frame type (%d) at %d is not compatible with keyframe interval\n", frm->i_type, frm->i_frame );
frm->i_type = h->param.b_open_gop && h->lookahead->i_last_keyframe >= 0 ? X264_TYPE_I : X264_TYPE_IDR;
}
}
if( frm->i_type == X264_TYPE_I && frm->i_frame - h->lookahead->i_last_keyframe >= h->param.i_keyint_min )
{
if( h->param.b_open_gop )
{
h->lookahead->i_last_keyframe = frm->i_frame; // Use display order
if( h->param.b_bluray_compat )
h->lookahead->i_last_keyframe -= bframes; // Use bluray order
frm->b_keyframe = 1;
}
else
frm->i_type = X264_TYPE_IDR;
}
if( frm->i_type == X264_TYPE_IDR )
{
/* Close GOP */
//设置当前帧为“上一个关键帧”
h->lookahead->i_last_keyframe = frm->i_frame;
frm->b_keyframe = 1;
if( bframes > 0 )
{
bframes--;
h->lookahead->next.list[bframes]->i_type = X264_TYPE_P;
}
}

if( bframes == h->param.i_bframe ||
!h->lookahead->next.list[bframes+1] )
{
if( IS_X264_TYPE_B( frm->i_type ) )
x264_log( h, X264_LOG_WARNING, "specified frame type is not compatible with max B-frames\n" );
if( frm->i_type == X264_TYPE_AUTO
|| IS_X264_TYPE_B( frm->i_type ) )
frm->i_type = X264_TYPE_P;
}

if( frm->i_type == X264_TYPE_BREF )
brefs++;

if( frm->i_type == X264_TYPE_AUTO )
frm->i_type = X264_TYPE_B;

else if( !IS_X264_TYPE_B( frm->i_type ) ) break;
}

if( bframes )
h->lookahead->next.list[bframes-1]->b_last_minigop_bframe = 1;
h->lookahead->next.list[bframes]->i_bframes = bframes;

/* insert a bref into the sequence */
if( h->param.i_bframe_pyramid && bframes > 1 && !brefs )
{
h->lookahead->next.list[bframes/2]->i_type = X264_TYPE_BREF;
brefs++;
}

/* calculate the frame costs ahead of time for x264_rc_analyse_slice while we still have lowres */
if( h->param.rc.i_rc_method != X264_RC_CQP )
{
x264_mb_analysis_t a;
int p0, p1, b;
p1 = b = bframes + 1;

x264_lowres_context_init( h, &a );

frames[0] = h->lookahead->last_nonb;
memcpy( &frames[1], h->lookahead->next.list, (bframes+1) * sizeof(x264_frame_t*) );
if( IS_X264_TYPE_I( h->lookahead->next.list[bframes]->i_type ) )
p0 = bframes + 1;
else // P
p0 = 0;

x264_slicetype_frame_cost( h, &a, frames, p0, p1, b, 0 );

if( (p0 != p1 || bframes) && h->param.rc.i_vbv_buffer_size )
{
/* We need the intra costs for row SATDs. */
x264_slicetype_frame_cost( h, &a, frames, b, b, b, 0 );

/* We need B-frame costs for row SATDs. */
p0 = 0;
for( b = 1; b <= bframes; b++ )
{
if( frames->i_type == X264_TYPE_B )
for( p1 = b; frames[p1]->i_type == X264_TYPE_B; )
p1++;
else
p1 = bframes + 1;
x264_slicetype_frame_cost( h, &a, frames, p0, p1, b, 0 );
if( frames[b]->i_type == X264_TYPE_BREF )
p0 = b;
}
}
}

/* Analyse for weighted P frames */
if( !h->param.rc.b_stat_read && h->lookahead->next.list[bframes]->i_type == X264_TYPE_P
&& h->param.analyse.i_weighted_pred >= X264_WEIGHTP_SIMPLE )
{
x264_emms();
x264_weights_analyse( h, h->lookahead->next.list[bframes], h->lookahead->last_nonb, 0 );
}

/* shift sequence to coded order.
use a small temporary list to avoid shifting the entire next buffer around */
int i_coded = h->lookahead->next.list[0]->i_frame;
if( bframes )
{
int idx_list[] = { brefs+1, 1 };
for( int i = 0; i < bframes; i++ )
{
int idx = idx_list[h->lookahead->next.list[i]->i_type == X264_TYPE_BREF]++;
frames[idx] = h->lookahead->next.list[i];
frames[idx]->i_reordered_pts = h->lookahead->next.list[idx]->i_pts;
}
frames[0] = h->lookahead->next.list[bframes];
frames[0]->i_reordered_pts = h->lookahead->next.list[0]->i_pts;
memcpy( h->lookahead->next.list, frames, (bframes+1) * sizeof(x264_frame_t*) );
}

for( int i = 0; i <= bframes; i++ )
{
h->lookahead->next.list[i]->i_coded = i_coded++;
if( i )
{
x264_calculate_durations( h, h->lookahead->next.list[i], h->lookahead->next.list[i-1], &h->i_cpb_delay, &h->i_coded_fields );
h->lookahead->next.list[0]->f_planned_cpb_duration[i-1] = (double)h->lookahead->next.list[i]->i_cpb_duration *
h->sps->vui.i_num_units_in_tick / h->sps->vui.i_time_scale;
}
else
x264_calculate_durations( h, h->lookahead->next.list[i], NULL, &h->i_cpb_delay, &h->i_coded_fields );
}
}

x264_slicetype_decide()源代码比较长，还没有细看。该函数中调用了一个比较重要的函数x264_slicetype_analyse()。

x264_slicetype_analyse()
x264_slicetype_analyse()用于分析帧类型。该函数的定义位于encoder\slicetype.c，如下所示。

//分析帧的类型（I、B、P） void x264_slicetype_analyse( x264_t *h, int intra_minigop ) { x264_mb_analysis_t a; x264_frame_t *frames[X264_LOOKAHEAD_MAX+3] = { NULL, }; int num_frames, orig_num_frames, keyint_limit, framecnt; int i_mb_count = NUM_MBS; int cost1p0, cost2p0, cost1b1, cost2p1; // 确定最大的搜索长度 // 在我的调试当中， h->lookahead->next.i_size = 4 int i_max_search = X264_MIN( h->lookahead->next.i_size, X264_LOOKAHEAD_MAX ); int vbv_lookahead = h->param.rc.i_vbv_buffer_size && h->param.rc.i_lookahead; /* For determinism we should limit the search to the number of frames lookahead has for sure * in h->lookahead->next.list buffer, except at the end of stream. * For normal calls with (intra_minigop == 0) that is h->lookahead->i_slicetype_length + 1 frames. * And for I-frame calls (intra_minigop != 0) we already removed intra_minigop frames from there. */ if( h->param.b_deterministic ) i_max_search = X264_MIN( i_max_search, h->lookahead->i_slicetype_length + 1 - intra_minigop ); int keyframe = !!intra_minigop; assert( h->frames.b_have_lowres ); if( !h->lookahead->last_nonb ) return; //frames[0]指向上一次的非B帧 frames[0] = h->lookahead->last_nonb; //frames[] 依次指向 lookahead->next链表中的帧 for( framecnt = 0; framecnt < i_max_search && h->lookahead->next.list[framecnt]->i_type == X264_TYPE_AUTO; framecnt++ ) frames[framecnt+1] = h->lookahead->next.list[framecnt]; x264_lowres_context_init( h, &a ); if( !framecnt ) { if( h->param.rc.b_mb_tree ) x264_macroblock_tree( h, &a, frames, 0, keyframe ); return; } keyint_limit = h->param.i_keyint_max - frames[0]->i_frame + h->lookahead->i_last_keyframe - 1; orig_num_frames = num_frames = h->param.b_intra_refresh ? framecnt : X264_MIN( framecnt, keyint_limit ); /* This is important psy-wise: if we have a non-scenecut keyframe, * there will be significant visual artifacts if the frames just before * go down in quality due to being referenced less, despite it being * more RD-optimal. */ if( (h->param.analyse.b_psy && h->param.rc.b_mb_tree) || vbv_lookahead ) num_frames = framecnt; else if( h->param.b_open_gop && num_frames < framecnt ) num_frames++; else if( num_frames == 0 ) { frames[1]->i_type = X264_TYPE_I; return; } int num_bframes = 0; int num_analysed_frames = num_frames; int reset_start; //通过scenecut()函数判断是否有场景切换，从而确定I帧 if( h->param.i_scenecut_threshold && scenecut( h, &a, frames, 0, 1, 1, orig_num_frames, i_max_search ) ) { frames[1]->i_type = X264_TYPE_I; return; } #if HAVE_OPENCL x264_opencl_slicetype_prep( h, frames, num_frames, a.i_lambda ); #endif //允许有B帧的时候 if( h->param.i_bframe ) { if( h->param.i_bframe_adaptive == X264_B_ADAPT_TRELLIS ) { if( num_frames > 1 ) { char best_paths[X264_BFRAME_MAX+1][X264_LOOKAHEAD_MAX+1] = {"","P"}; int best_path_index = num_frames % (X264_BFRAME_MAX+1); /* Perform the frametype analysis. */ for( int j = 2; j <= num_frames; j++ ) x264_slicetype_path( h, &a, frames, j, best_paths ); num_bframes = strspn( best_paths[best_path_index], "B" ); /* Load the results of the analysis into the frame types. */ for( int j = 1; j < num_frames; j++ ) frames[j]->i_type = best_paths[best_path_index][j-1] == 'B' ? X264_TYPE_B : X264_TYPE_P; } frames[num_frames]->i_type = X264_TYPE_P; } else if( h->param.i_bframe_adaptive == X264_B_ADAPT_FAST ) { for( int i = 0; i <= num_frames-2; ) { //i+2作为Ｐ帧编码的代价 //注：i+2始终为P帧 cost2p1 = x264_slicetype_frame_cost( h, &a, frames, i+0, i+2, i+2, 1 ); if( frames[i+2]->i_intra_mbs[2] > i_mb_count / 2 ) { frames[i+1]->i_type = X264_TYPE_P; frames[i+2]->i_type = X264_TYPE_P; i += 2; continue; } #if HAVE_OPENCL if( h->param.b_opencl ) { int b_work_done = 0; b_work_done |= x264_opencl_precalculate_frame_cost(h, frames, a.i_lambda, i+0, i+2, i+1 ); b_work_done |= x264_opencl_precalculate_frame_cost(h, frames, a.i_lambda, i+0, i+1, i+1 ); b_work_done |= x264_opencl_precalculate_frame_cost(h, frames, a.i_lambda, i+1, i+2, i+2 ); if( b_work_done ) x264_opencl_flush( h ); } #endif //计算代价 //x264_slicetype_frame_cost(,,,p0,p1,b,) //p0 b p1 //p1!=b为B帧，否则为P帧 // i + 1 作为B帧编码的代价 cost1b1 = x264_slicetype_frame_cost( h, &a, frames, i+0, i+2, i+1, 0 ); // i + 1 作为P帧编码的代价 cost1p0 = x264_slicetype_frame_cost( h, &a, frames, i+0, i+1, i+1, 0 ); // i + 2 作为P帧编码的代价 cost2p0 = x264_slicetype_frame_cost( h, &a, frames, i+1, i+2, i+2, 0 ); //如果i+1作为P帧编码的代价　+ i+2作为P帧编码的代价 //小于 i+1作为B帧编码的代价 + i+2作为P帧编码的代价 if( cost1p0 + cost2p0 < cost1b1 + cost2p1 ) { //那么i+1将作为P帧编码 //然后直接continue frames[i+1]->i_type = X264_TYPE_P; i += 1; continue; } // arbitrary and untuned #define INTER_THRESH 300 #define P_SENS_BIAS (50 - h->param.i_bframe_bias) // i+1 将作为B帧编码 frames[i+1]->i_type = X264_TYPE_B; int j; for( j = i+2; j <= X264_MIN( i+h->param.i_bframe, num_frames-1 ); j++ ) { int pthresh = X264_MAX(INTER_THRESH - P_SENS_BIAS * (j-i-1), INTER_THRESH/10); // 预测j+1作为P帧编码代价 int pcost = x264_slicetype_frame_cost( h, &a, frames, i+0, j+1, j+1, 1 ); // 如果pcost 满足下述条件，则确定了一个P帧，跳出循环 if( pcost > pthresh*i_mb_count || frames[j+1]->i_intra_mbs[j-i+1] > i_mb_count/3 ) break; // 否则就是B帧 frames[j]->i_type = X264_TYPE_B; } // 将j帧确定为P帧 frames[j]->i_type = X264_TYPE_P; i = j; } // 最后一帧确定为P帧 frames[num_frames]->i_type = X264_TYPE_P; num_bframes = 0; // 确定有多少个B帧 while( num_bframes < num_frames && frames[num_bframes+1]->i_type == X264_TYPE_B ) num_bframes++; } else { // 确定多少B帧 num_bframes = X264_MIN(num_frames-1, h->param.i_bframe); // 每num_bframes + 1一个P帧，其余皆为B帧 for( int j = 1; j < num_frames; j++ ) frames[j]->i_type = (j%(num_bframes+1)) ? X264_TYPE_B : X264_TYPE_P; // 最后一帧为P帧 frames[num_frames]->i_type = X264_TYPE_P; } /* Check scenecut on the first minigop. */ // 如果B帧中，有帧有场景切换，则改变其为P帧 for( int j = 1; j < num_bframes+1; j++ ) if( h->param.i_scenecut_threshold && scenecut( h, &a, frames, j, j+1, 0, orig_num_frames, i_max_search ) ) { frames[j]->i_type = X264_TYPE_P; num_analysed_frames = j; break; } reset_start = keyframe ? 1 : X264_MIN( num_bframes+2, num_analysed_frames+1 ); } else { //h->param.i_bframe为 0 //则所有的帧皆为P帧 for( int j = 1; j <= num_frames; j++ ) frames[j]->i_type = X264_TYPE_P; reset_start = !keyframe + 1; num_bframes = 0; } /* Perform the actual macroblock tree analysis. * Don't go farther than the maximum keyframe interval; this helps in short GOPs. */ if( h->param.rc.b_mb_tree ) x264_macroblock_tree( h, &a, frames, X264_MIN(num_frames, h->param.i_keyint_max), keyframe ); /* Enforce keyframe limit. */ if( !h->param.b_intra_refresh ) for( int i = keyint_limit+1; i <= num_frames; i += h->param.i_keyint_max ) { //迫使为I帧 frames[i]->i_type = X264_TYPE_I; reset_start = X264_MIN( reset_start, i+1 ); if( h->param.b_open_gop && h->param.b_bluray_compat ) while( IS_X264_TYPE_B( frames[i-1]->i_type ) ) i--; } if( vbv_lookahead ) x264_vbv_lookahead( h, &a, frames, num_frames, keyframe ); /* Restore frametypes for all frames that haven't actually been decided yet. */ for( int j = reset_start; j <= num_frames; j++ ) frames[j]->i_type = X264_TYPE_AUTO; #if HAVE_OPENCL x264_opencl_slicetype_end( h ); #endif }

通过源代码可以看出，x264_slicetype_analyse()分析了frames[]队列中的视频帧的帧类型。简单总结一下该函数的流程：

（1）如果frames[1]通过scenecut()判断为场景切换，设置为I帧，并且直接返回。

（2）如果i_bframe为0，即不使用B帧，则将所有帧都设置为P帧。

（3）如果i_bframe不为0，即使用B帧，则需要进行比较复杂的帧开销计算。这时候需要调用一帧图像开销的计算函数x264_slicetype_frame_cost()。
有关帧类型判断在代码中已经做了注释，不再详细记录，下文继续看一下x264_slicetype_frame_cost()函数。

x264_slicetype_frame_cost()
x264_slicetype_frame_cost()用于计算一帧图像的开销。该函数的定义位于encoder\slicetype.c，如下所示。

//一帧图像的开销 //x264_slicetype_frame_cost(,,,p0,p1,b,) // p0 b p1 static int x264_slicetype_frame_cost( x264_t *h, x264_mb_analysis_t *a, x264_frame_t **frames, int p0, int p1, int b, int b_intra_penalty ) { int i_score = 0; int do_search[2]; const x264_weight_t *w = x264_weight_none; x264_frame_t *fenc = frames[b]; /* Check whether we already evaluated this frame * If we have tried this frame as P, then we have also tried * the preceding frames as B. (is this still true?) */ /* Also check that we already calculated the row SATDs for the current frame. */ //如果已经计算过就不用算了 if( fenc->i_cost_est[b-p0][p1-b] >= 0 && (!h->param.rc.i_vbv_buffer_size || fenc->i_row_satds[b-p0][p1-b][0] != -1) ) i_score = fenc->i_cost_est[b-p0][p1-b]; else { int dist_scale_factor = 128; /* For each list, check to see whether we have lowres motion-searched this reference frame before. */ do_search[0] = b != p0 && fenc->lowres_mvs[0][b-p0-1][0][0] == 0x7FFF; do_search[1] = b != p1 && fenc->lowres_mvs[1][p1-b-1][0][0] == 0x7FFF; if( do_search[0] ) { if( h->param.analyse.i_weighted_pred && b == p1 ) { x264_emms(); x264_weights_analyse( h, fenc, frames[p0], 1 ); w = fenc->weight[0]; } fenc->lowres_mvs[0][b-p0-1][0][0] = 0; } if( do_search[1] ) fenc->lowres_mvs[1][p1-b-1][0][0] = 0; if( p1 != p0 ) dist_scale_factor = ( ((b-p0) << 8) + ((p1-p0) >> 1) ) / (p1-p0); int output_buf_size = h->mb.i_mb_height + (NUM_INTS + PAD_SIZE) * h->param.i_lookahead_threads; int *output_inter[X264_LOOKAHEAD_THREAD_MAX+1]; int *output_intra[X264_LOOKAHEAD_THREAD_MAX+1]; output_inter[0] = h->scratch_buffer2; output_intra[0] = output_inter[0] + output_buf_size; #if HAVE_OPENCL if( h->param.b_opencl ) { x264_opencl_lowres_init(h, fenc, a->i_lambda ); if( do_search[0] ) { x264_opencl_lowres_init( h, frames[p0], a->i_lambda ); x264_opencl_motionsearch( h, frames, b, p0, 0, a->i_lambda, w ); } if( do_search[1] ) { x264_opencl_lowres_init( h, frames[p1], a->i_lambda ); x264_opencl_motionsearch( h, frames, b, p1, 1, a->i_lambda, NULL ); } if( b != p0 ) x264_opencl_finalize_cost( h, a->i_lambda, frames, p0, p1, b, dist_scale_factor ); x264_opencl_flush( h ); i_score = fenc->i_cost_est[b-p0][p1-b]; } else #endif { if( h->param.i_lookahead_threads > 1 ) { x264_slicetype_slice_t s[X264_LOOKAHEAD_THREAD_MAX]; for( int i = 0; i < h->param.i_lookahead_threads; i++ ) { x264_t *t = h->lookahead_thread[i]; /* FIXME move this somewhere else */ t->mb.i_me_method = h->mb.i_me_method; t->mb.i_subpel_refine = h->mb.i_subpel_refine; t->mb.b_chroma_me = h->mb.b_chroma_me; s[i] = (x264_slicetype_slice_t){ t, a, frames, p0, p1, b, dist_scale_factor, do_search, w, output_inter[i], output_intra[i] }; t->i_threadslice_start = ((h->mb.i_mb_height * i + h->param.i_lookahead_threads/2) / h->param.i_lookahead_threads); t->i_threadslice_end = ((h->mb.i_mb_height * (i+1) + h->param.i_lookahead_threads/2) / h->param.i_lookahead_threads); int thread_height = t->i_threadslice_end - t->i_threadslice_start; int thread_output_size = thread_height + NUM_INTS; memset( output_inter[i], 0, thread_output_size * sizeof(int) ); memset( output_intra[i], 0, thread_output_size * sizeof(int) ); output_inter[i][NUM_ROWS] = output_intra[i][NUM_ROWS] = thread_height; output_inter[i+1] = output_inter[i] + thread_output_size + PAD_SIZE; output_intra[i+1] = output_intra[i] + thread_output_size + PAD_SIZE; x264_threadpool_run( h->lookaheadpool, (void*)x264_slicetype_slice_cost, &s[i] ); } for( int i = 0; i < h->param.i_lookahead_threads; i++ ) x264_threadpool_wait( h->lookaheadpool, &s[i] ); } else { h->i_threadslice_start = 0; h->i_threadslice_end = h->mb.i_mb_height; memset( output_inter[0], 0, (output_buf_size - PAD_SIZE) * sizeof(int) ); memset( output_intra[0], 0, (output_buf_size - PAD_SIZE) * sizeof(int) ); output_inter[0][NUM_ROWS] = output_intra[0][NUM_ROWS] = h->mb.i_mb_height; //作为参数的结构体 x264_slicetype_slice_t s = (x264_slicetype_slice_t){ h, a, frames, p0, p1, b, dist_scale_factor, do_search, w, output_inter[0], output_intra[0] }; //一个slice的开销 //输入输出参数都在s结构体中 x264_slicetype_slice_cost( &s ); } /* Sum up accumulators */ if( b == p1 ) fenc->i_intra_mbs[b-p0] = 0; if( !fenc->b_intra_calculated ) { fenc->i_cost_est[0][0] = 0; fenc->i_cost_est_aq[0][0] = 0; } fenc->i_cost_est[b-p0][p1-b] = 0; fenc->i_cost_est_aq[b-p0][p1-b] = 0; int *row_satd_inter = fenc->i_row_satds[b-p0][p1-b]; int *row_satd_intra = fenc->i_row_satds[0][0]; for( int i = 0; i < h->param.i_lookahead_threads; i++ ) { //累加output_inter[]或output_intra[] //这2个变量中存储了整帧的开销 if( b == p1 ) fenc->i_intra_mbs[b-p0] += output_inter[i][INTRA_MBS]; if( !fenc->b_intra_calculated ) { //帧内编码的代价 fenc->i_cost_est[0][0] += output_intra[i][COST_EST]; fenc->i_cost_est_aq[0][0] += output_intra[i][COST_EST_AQ]; } //帧间编码的代价 fenc->i_cost_est[b-p0][p1-b] += output_inter[i][COST_EST]; fenc->i_cost_est_aq[b-p0][p1-b] += output_inter[i][COST_EST_AQ]; if( h->param.rc.i_vbv_buffer_size ) { int row_count = output_inter[i][NUM_ROWS]; memcpy( row_satd_inter, output_inter[i] + NUM_INTS, row_count * sizeof(int) ); if( !fenc->b_intra_calculated ) memcpy( row_satd_intra, output_intra[i] + NUM_INTS, row_count * sizeof(int) ); row_satd_inter += row_count; row_satd_intra += row_count; } } //一帧的开销 i_score = fenc->i_cost_est[b-p0][p1-b]; if( b != p1 )//B帧 i_score = (uint64_t)i_score * 100 / (120 + h->param.i_bframe_bias); else fenc->b_intra_calculated = 1; fenc->i_cost_est[b-p0][p1-b] = i_score; x264_emms(); } } if( b_intra_penalty ) { // arbitrary penalty for I-blocks after B-frames int nmb = NUM_MBS; i_score += (uint64_t)i_score * fenc->i_intra_mbs[b-p0] / (nmb * 8); } //返回一帧的开销值 return i_score; }

从源代码可以看出，x264_slicetype_analyse()调用了x264_slicetype_slice_cost()来计算一个slice的开销。

x264_slicetype_slice_cost()
x264_slicetype_slice_cost()用来计算一个slice的开销。该函数的定义位于encoder\slicetype.c，如下所示。

//一个slice的开销 static void x264_slicetype_slice_cost( x264_slicetype_slice_t *s ) { x264_t *h = s->h; /* Lowres lookahead goes backwards because the MVs are used as predictors in the main encode. * This considerably improves MV prediction overall. */ /* The edge mbs seem to reduce the predictive quality of the * whole frame's score, but are needed for a spatial distribution. */ int do_edges = h->param.rc.b_mb_tree || h->param.rc.i_vbv_buffer_size || h->mb.i_mb_width <= 2 || h->mb.i_mb_height <= 2; int start_y = X264_MIN( h->i_threadslice_end - 1, h->mb.i_mb_height - 2 + do_edges ); int end_y = X264_MAX( h->i_threadslice_start, 1 - do_edges ); int start_x = h->mb.i_mb_width - 2 + do_edges; int end_x = 1 - do_edges; //逐个计算每个MB的开销 for( h->mb.i_mb_y = start_y; h->mb.i_mb_y >= end_y; h->mb.i_mb_y-- ) for( h->mb.i_mb_x = start_x; h->mb.i_mb_x >= end_x; h->mb.i_mb_x-- ) x264_slicetype_mb_cost( h, s->a, s->frames, s->p0, s->p1, s->b, s->dist_scale_factor, s->do_search, s->w, s->output_inter, s->output_intra ); }

从源代码可以看出，x264_slicetype_slice_cost()循环遍历了每一个宏块，针对每一个宏块调用了x264_slicetype_mb_cost()。

x264_slicetype_mb_cost()
x264_slicetype_mb_cost()用于计算一个宏块的编码代价。该函数的定义位于encoder\slicetype.c，如下所示。

//一个MB的开销 static void x264_slicetype_mb_cost( x264_t *h, x264_mb_analysis_t *a, x264_frame_t **frames, int p0, int p1, int b, int dist_scale_factor, int do_search[2], const x264_weight_t *w, int *output_inter, int *output_intra ) { x264_frame_t *fref0 = frames[p0]; x264_frame_t *fref1 = frames[p1]; x264_frame_t *fenc = frames[b]; const int b_bidir = (b < p1); const int i_mb_x = h->mb.i_mb_x; const int i_mb_y = h->mb.i_mb_y; const int i_mb_stride = h->mb.i_mb_width; const int i_mb_xy = i_mb_x + i_mb_y * i_mb_stride; const int i_stride = fenc->i_stride_lowres; const int i_pel_offset = 8 * (i_mb_x + i_mb_y * i_stride); const int i_bipred_weight = h->param.analyse.b_weighted_bipred ? 64 - (dist_scale_factor>>2) : 32; int16_t (*fenc_mvs[2])[2] = { &fenc->lowres_mvs[0][b-p0-1][i_mb_xy], &fenc->lowres_mvs[1][p1-b-1][i_mb_xy] }; int (*fenc_costs[2]) = { &fenc->lowres_mv_costs[0][b-p0-1][i_mb_xy], &fenc->lowres_mv_costs[1][p1-b-1][i_mb_xy] }; int b_frame_score_mb = (i_mb_x > 0 && i_mb_x < h->mb.i_mb_width - 1 && i_mb_y > 0 && i_mb_y < h->mb.i_mb_height - 1) || h->mb.i_mb_width <= 2 || h->mb.i_mb_height <= 2; ALIGNED_ARRAY_16( pixel, pix1,[9*FDEC_STRIDE] ); pixel *pix2 = pix1+8; x264_me_t m[2]; int i_bcost = COST_MAX; int list_used = 0; /* A small, arbitrary bias to avoid VBV problems caused by zero-residual lookahead blocks. */ int lowres_penalty = 4; //计算只涉及一个分量 h->mb.pic.p_fenc[0] = h->mb.pic.fenc_buf; //从低分辨率（1/2线性内插）图像中拷贝数据 h->mc.copy[PIXEL_8x8]( h->mb.pic.p_fenc[0], FENC_STRIDE, &fenc->lowres[0][i_pel_offset], i_stride, 8 ); if( p0 == p1 ) goto lowres_intra_mb; // no need for h->mb.mv_min[] h->mb.mv_limit_fpel[0][0] = -8*h->mb.i_mb_x - 4; h->mb.mv_limit_fpel[1][0] = 8*( h->mb.i_mb_width - h->mb.i_mb_x - 1 ) + 4; h->mb.mv_min_spel[0] = 4*( h->mb.mv_limit_fpel[0][0] - 8 ); h->mb.mv_max_spel[0] = 4*( h->mb.mv_limit_fpel[1][0] + 8 ); if( h->mb.i_mb_x >= h->mb.i_mb_width - 2 ) { h->mb.mv_limit_fpel[0][1] = -8*h->mb.i_mb_y - 4; h->mb.mv_limit_fpel[1][1] = 8*( h->mb.i_mb_height - h->mb.i_mb_y - 1 ) + 4; h->mb.mv_min_spel[1] = 4*( h->mb.mv_limit_fpel[0][1] - 8 ); h->mb.mv_max_spel[1] = 4*( h->mb.mv_limit_fpel[1][1] + 8 ); } #define LOAD_HPELS_LUMA(dst, src) \ { \ (dst)[0] = &(src)[0][i_pel_offset]; \ (dst)[1] = &(src)[1][i_pel_offset]; \ (dst)[2] = &(src)[2][i_pel_offset]; \ (dst)[3] = &(src)[3][i_pel_offset]; \ } #define LOAD_WPELS_LUMA(dst,src) \ (dst) = &(src)[i_pel_offset]; #define CLIP_MV( mv ) \ { \ mv[0] = x264_clip3( mv[0], h->mb.mv_min_spel[0], h->mb.mv_max_spel[0] ); \ mv[1] = x264_clip3( mv[1], h->mb.mv_min_spel[1], h->mb.mv_max_spel[1] ); \ } #define TRY_BIDIR( mv0, mv1, penalty ) \ { \ int i_cost; \ if( h->param.analyse.i_subpel_refine <= 1 ) \ { \ int hpel_idx1 = (((mv0)[0]&2)>>1) + ((mv0)[1]&2); \ int hpel_idx2 = (((mv1)[0]&2)>>1) + ((mv1)[1]&2); \ pixel *src1 = m[0].p_fref[hpel_idx1] + ((mv0)[0]>>2) + ((mv0)[1]>>2) * m[0].i_stride[0]; \ pixel *src2 = m[1].p_fref[hpel_idx2] + ((mv1)[0]>>2) + ((mv1)[1]>>2) * m[1].i_stride[0]; \ h->mc.avg[PIXEL_8x8]( pix1, 16, src1, m[0].i_stride[0], src2, m[1].i_stride[0], i_bipred_weight ); \ } \ else \ { \ intptr_t stride1 = 16, stride2 = 16; \ pixel *src1, *src2; \ src1 = h->mc.get_ref( pix1, &stride1, m[0].p_fref, m[0].i_stride[0], \ (mv0)[0], (mv0)[1], 8, 8, w ); \ src2 = h->mc.get_ref( pix2, &stride2, m[1].p_fref, m[1].i_stride[0], \ (mv1)[0], (mv1)[1], 8, 8, w ); \ h->mc.avg[PIXEL_8x8]( pix1, 16, src1, stride1, src2, stride2, i_bipred_weight ); \ } \ i_cost = penalty * a->i_lambda + h->pixf.mbcmp[PIXEL_8x8]( \ m[0].p_fenc[0], FENC_STRIDE, pix1, 16 ); \ COPY2_IF_LT( i_bcost, i_cost, list_used, 3 ); \ } //帧间编码（后面还有帧内编码） //处理m[0] m[0].i_pixel = PIXEL_8x8; m[0].p_cost_mv = a->p_cost_mv; m[0].i_stride[0] = i_stride; m[0].p_fenc[0] = h->mb.pic.p_fenc[0]; m[0].weight = w; m[0].i_ref = 0; //加载1/2插值像素点 LOAD_HPELS_LUMA( m[0].p_fref, fref0->lowres ); m[0].p_fref_w = m[0].p_fref[0]; if( w[0].weightfn ) LOAD_WPELS_LUMA( m[0].p_fref_w, fenc->weighted[0] ); //双线预测，处理m[1] if( b_bidir ) { int16_t *mvr = fref1->lowres_mvs[0][p1-p0-1][i_mb_xy]; ALIGNED_ARRAY_8( int16_t, dmv,[2],[2] ); m[1].i_pixel = PIXEL_8x8; m[1].p_cost_mv = a->p_cost_mv; m[1].i_stride[0] = i_stride; m[1].p_fenc[0] = h->mb.pic.p_fenc[0]; m[1].i_ref = 0; m[1].weight = x264_weight_none; LOAD_HPELS_LUMA( m[1].p_fref, fref1->lowres ); m[1].p_fref_w = m[1].p_fref[0]; dmv[0][0] = ( mvr[0] * dist_scale_factor + 128 ) >> 8; dmv[0][1] = ( mvr[1] * dist_scale_factor + 128 ) >> 8; dmv[1][0] = dmv[0][0] - mvr[0]; dmv[1][1] = dmv[0][1] - mvr[1]; CLIP_MV( dmv[0] ); CLIP_MV( dmv[1] ); if( h->param.analyse.i_subpel_refine <= 1 ) M64( dmv ) &= ~0x0001000100010001ULL; /* mv & ~1 */ //双向预测，其中包含了mc.avg[PIXEL_8x8]() TRY_BIDIR( dmv[0], dmv[1], 0 ); if( M64( dmv ) ) { int i_cost; h->mc.avg[PIXEL_8x8]( pix1, 16, m[0].p_fref[0], m[0].i_stride[0], m[1].p_fref[0], m[1].i_stride[0], i_bipred_weight ); i_cost = h->pixf.mbcmp[PIXEL_8x8]( m[0].p_fenc[0], FENC_STRIDE, pix1, 16 ); COPY2_IF_LT( i_bcost, i_cost, list_used, 3 ); } } for( int l = 0; l < 1 + b_bidir; l++ ) { if( do_search[l] ) { int i_mvc = 0; int16_t (*fenc_mv)[2] = fenc_mvs[l]; ALIGNED_4( int16_t mvc[4][2] ); /* Reverse-order MV prediction. */ M32( mvc[0] ) = 0; M32( mvc[2] ) = 0; #define MVC(mv) { CP32( mvc[i_mvc], mv ); i_mvc++; } if( i_mb_x < h->mb.i_mb_width - 1 ) MVC( fenc_mv[1] ); if( i_mb_y < h->i_threadslice_end - 1 ) { MVC( fenc_mv[i_mb_stride] ); if( i_mb_x > 0 ) MVC( fenc_mv[i_mb_stride-1] ); if( i_mb_x < h->mb.i_mb_width - 1 ) MVC( fenc_mv[i_mb_stride+1] ); } #undef MVC if( i_mvc <= 1 ) CP32( m[l].mvp, mvc[0] ); else x264_median_mv( m[l].mvp, mvc[0], mvc[1], mvc[2] ); /* Fast skip for cases of near-zero residual. Shortcut: don't bother except in the mv0 case, * since anything else is likely to have enough residual to not trigger the skip. */ if( !M32( m[l].mvp ) ) { m[l].cost = h->pixf.mbcmp[PIXEL_8x8]( m[l].p_fenc[0], FENC_STRIDE, m[l].p_fref[0], m[l].i_stride[0] ); if( m[l].cost < 64 ) { M32( m[l].mv ) = 0; goto skip_motionest; } } //运动搜索，开销存在m[l].cost中 x264_me_search( h, &m[l], mvc, i_mvc ); m[l].cost -= a->p_cost_mv[0]; // remove mvcost from skip mbs if( M32( m[l].mv ) ) m[l].cost += 5 * a->i_lambda; skip_motionest: CP32( fenc_mvs[l], m[l].mv ); *fenc_costs[l] = m[l].cost; } else { CP32( m[l].mv, fenc_mvs[l] ); m[l].cost = *fenc_costs[l]; } //如果更小就拷贝 //帧间编码开销，存储于i_bcost COPY2_IF_LT( i_bcost, m[l].cost, list_used, l+1 ); } if( b_bidir && ( M32( m[0].mv ) || M32( m[1].mv ) ) ) TRY_BIDIR( m[0].mv, m[1].mv, 5 ); lowres_intra_mb: //帧内编码 if( !fenc->b_intra_calculated ) { ALIGNED_ARRAY_16( pixel, edge,[36] ); pixel *pix = &pix1[8+FDEC_STRIDE]; pixel *src = &fenc->lowres[0][i_pel_offset]; const int intra_penalty = 5 * a->i_lambda; int satds[3]; int pixoff = 4 / sizeof(pixel); /* Avoid store forwarding stalls by writing larger chunks */ memcpy( pix-FDEC_STRIDE, src-i_stride, 16 * sizeof(pixel) ); for( int i = -1; i < 8; i++ ) M32( &pix[i*FDEC_STRIDE-pixoff] ) = M32( &src[i*i_stride-pixoff] ); //8x8块的SAD/SATD计算 //x3打表计算了V，H，DC三种模式，开销存储在satds[3]数组的3个元素中 h->pixf.intra_mbcmp_x3_8x8c( h->mb.pic.p_fenc[0], pix, satds ); //帧内编码开销，存储于i_icost int i_icost = X264_MIN3( satds[0], satds[1], satds[2] ); if( h->param.analyse.i_subpel_refine > 1 ) { h->predict_8x8c[I_PRED_CHROMA_P]( pix ); int satd = h->pixf.mbcmp[PIXEL_8x8]( pix, FDEC_STRIDE, h->mb.pic.p_fenc[0], FENC_STRIDE ); i_icost = X264_MIN( i_icost, satd ); h->predict_8x8_filter( pix, edge, ALL_NEIGHBORS, ALL_NEIGHBORS ); for( int i = 3; i < 9; i++ ) { h->predict_8x8[i]( pix, edge ); satd = h->pixf.mbcmp[PIXEL_8x8]( pix, FDEC_STRIDE, h->mb.pic.p_fenc[0], FENC_STRIDE ); i_icost = X264_MIN( i_icost, satd ); } } i_icost += intra_penalty + lowres_penalty; //存一下 fenc->i_intra_cost[i_mb_xy] = i_icost; int i_icost_aq = i_icost; if( h->param.rc.i_aq_mode ) i_icost_aq = (i_icost_aq * fenc->i_inv_qscale_factor[i_mb_xy] + 128) >> 8; output_intra[ROW_SATD] += i_icost_aq; if( b_frame_score_mb ) { //累加。[COST_EST]用于整帧的开销计算 output_intra[COST_EST] += i_icost; output_intra[COST_EST_AQ] += i_icost_aq; } } i_bcost += lowres_penalty; /* forbid intra-mbs in B-frames, because it's rare and not worth checking */ /* FIXME: Should we still forbid them now that we cache intra scores? */ if( !b_bidir ) { int i_icost = fenc->i_intra_cost[i_mb_xy]; //帧内开销比帧间更小，b_intra就会取1 int b_intra = i_icost < i_bcost; if( b_intra ) { //赋值给i_bcost i_bcost = i_icost; list_used = 0; } if( b_frame_score_mb ) output_inter[INTRA_MBS] += b_intra;//[INTRA_MBS]统计有多少个帧内模式的宏块 } /* In an I-frame, we've already added the results above in the intra section. */ if( p0 != p1 ) { int i_bcost_aq = i_bcost; if( h->param.rc.i_aq_mode ) i_bcost_aq = (i_bcost_aq * fenc->i_inv_qscale_factor[i_mb_xy] + 128) >> 8; output_inter[ROW_SATD] += i_bcost_aq; if( b_frame_score_mb ) { /* Don't use AQ-weighted costs for slicetype decision, only for ratecontrol. */ //累加。[COST_EST]用于整帧的开销计算 output_inter[COST_EST] += i_bcost; output_inter[COST_EST_AQ] += i_bcost_aq; } } //存储开销i_bcost fenc->lowres_costs[b-p0][p1-b][i_mb_xy] = X264_MIN( i_bcost, LOWRES_COST_MASK ) + (list_used << LOWRES_COST_SHIFT); } #undef TRY_BIDIR

宏块开销这里在源代码上写了比较详细的注释，不再详细记录。在这里有一点需要注意：处理的图像是经过1/2线性差值的“低分辨率（lowres）”图片（这样速度更快？），而其中宏块的大小也是以8x8而不是16x16为单位的。

x264_frame_shift()
x264_frame_shift()用于从队列头部取出1帧。该函数的定义位于common\frame.c，如下所示。

//从队列的头部取出一帧 x264_frame_t *x264_frame_shift( x264_frame_t **list ) { x264_frame_t *frame = list[0]; int i; for( i = 0; list[i]; i++ ) list[i] = list[i+1]; assert(frame); return frame; }

从源代码可以看出，x264_frame_shift()取出了list[0]并且作为返回值返回。

x264_reference_update()
x264_reference_update()用于更新参考帧队列（将重建帧fdec加入参考帧队列）。该函数的定义位于encoder\encoder.c，如下所示。

//更新参考帧队列，若为非参考B帧则不更新 //重建帧移植参考帧列表，新建一个重建帧 static inline int x264_reference_update( x264_t *h ) { //如果不是被参考的帧 if( !h->fdec->b_kept_as_ref ) { if( h->i_thread_frames > 1 ) { x264_frame_push_unused( h, h->fdec ); h->fdec = x264_frame_pop_unused( h, 1 ); if( !h->fdec ) return -1; } return 0; } /* apply mmco from previous frame. */ for( int i = 0; i < h->sh.i_mmco_command_count; i++ ) for( int j = 0; h->frames.reference[j]; j++ ) if( h->frames.reference[j]->i_poc == h->sh.mmco[i].i_poc ) x264_frame_push_unused( h, x264_frame_shift( &h->frames.reference[j] ) ); /* move frame in the buffer */ //重建帧加入参考帧列表 x264_frame_push( h->frames.reference, h->fdec ); //列表满了，则要移除1帧 if( h->frames.reference[h->sps->i_num_ref_frames] ) x264_frame_push_unused( h, x264_frame_shift( h->frames.reference ) ); //重新初始化重建帧fdec h->fdec = x264_frame_pop_unused( h, 1 ); if( !h->fdec ) return -1; return 0; }

从源代码可以看出，如果重建帧fdec是不被参考的B帧，则直接返回；如果fdec是被参考的帧，则会调用x264_frame_push()将该帧加入frames.reference[]队列的尾部。如果frames.reference[]已经满了，则会调用x264_frame_shift()和x264_frame_push_unused()将frames.reference[]队列头部的帧移动到frames.unused[]队列。最后函数还会调用x264_frame_pop_unused()获取一个新的重建帧fdec。

x264_reference_reset()
如果编码帧为IDR帧，就会调用x264_reference_reset()函数清空参考帧列表。该函数定义位于encoder\encoder.c，如下所示。

//清空所有参考帧 static inline void x264_reference_reset( x264_t *h ) { //把frames.reference[]中所有帧移动到frames.unused[] while( h->frames.reference[0] ) x264_frame_push_unused( h, x264_frame_pop( h->frames.reference ) ); h->fdec->i_poc = h->fenc->i_poc = 0; }

从源代码可以看出，x264_reference_reset()中调用x264_frame_pop()和x264_frame_push_unused()将frames.reference[]队列中的帧移动到frames.unused[]队列中。

x264_slice_init()
x264_slice_init()用于创建Slice Header，初始化其中的信息。该函数的定义位于encoder\encoder.c，如下所示。

//创建Slice Header static inline void x264_slice_init( x264_t *h, int i_nal_type, int i_global_qp ) { /* ------------------------ Create slice header ----------------------- */ if( i_nal_type == NAL_SLICE_IDR ) { //I帧 //对x264_slice_header_t进行赋值 x264_slice_header_init( h, &h->sh, h->sps, h->pps, h->i_idr_pic_id, h->i_frame_num, i_global_qp ); /* alternate id */ if( h->param.i_avcintra_class ) { switch( h->i_idr_pic_id ) { case 5: h->i_idr_pic_id = 3; break; case 3: h->i_idr_pic_id = 4; break; case 4: default: h->i_idr_pic_id = 5; break; } } else h->i_idr_pic_id ^= 1; } else { //非IDR帧 x264_slice_header_init( h, &h->sh, h->sps, h->pps, -1, h->i_frame_num, i_global_qp ); //参考帧列表 h->sh.i_num_ref_idx_l0_active = h->i_ref[0] <= 0 ? 1 : h->i_ref[0]; h->sh.i_num_ref_idx_l1_active = h->i_ref[1] <= 0 ? 1 : h->i_ref[1]; if( h->sh.i_num_ref_idx_l0_active != h->pps->i_num_ref_idx_l0_default_active || (h->sh.i_type == SLICE_TYPE_B && h->sh.i_num_ref_idx_l1_active != h->pps->i_num_ref_idx_l1_default_active) ) { h->sh.b_num_ref_idx_override = 1; } } if( h->fenc->i_type == X264_TYPE_BREF && h->param.b_bluray_compat && h->sh.i_mmco_command_count ) { h->b_sh_backup = 1; h->sh_backup = h->sh; } h->fdec->i_frame_num = h->sh.i_frame_num; if( h->sps->i_poc_type == 0 ) { h->sh.i_poc = h->fdec->i_poc; if( PARAM_INTERLACED ) { h->sh.i_delta_poc_bottom = h->param.b_tff ? 1 : -1; h->sh.i_poc += h->sh.i_delta_poc_bottom == -1; } else h->sh.i_delta_poc_bottom = 0; h->fdec->i_delta_poc[0] = h->sh.i_delta_poc_bottom == -1; h->fdec->i_delta_poc[1] = h->sh.i_delta_poc_bottom == 1; } else { /* Nothing to do ? */ } //主要对mb结构体赋初值 x264_macroblock_slice_init( h ); }

从源代码可以看出，x264_slice_init()调用x264_slice_header_init()完成了Slice Header “通用”的初始化工作，然后根据帧类型的不同，做了一些特殊参数的设置。下面看一下x264_slice_header_init()。

x264_slice_header_init()
x264_slice_header_init()用于对Slice Header进行初始化工作。该函数的定义如下所示。

/* Fill "default" values */ //对x264_slice_header_t进行赋值 static void x264_slice_header_init( x264_t *h, x264_slice_header_t *sh, x264_sps_t *sps, x264_pps_t *pps, int i_idr_pic_id, int i_frame, int i_qp ) { x264_param_t *param = &h->param; /* First we fill all fields */ sh->sps = sps; sh->pps = pps; sh->i_first_mb = 0; sh->i_last_mb = h->mb.i_mb_count - 1; sh->i_pps_id = pps->i_id; sh->i_frame_num = i_frame; sh->b_mbaff = PARAM_INTERLACED; sh->b_field_pic = 0; /* no field support for now */ sh->b_bottom_field = 0; /* not yet used */ sh->i_idr_pic_id = i_idr_pic_id; /* poc stuff, fixed later */ sh->i_poc = 0; sh->i_delta_poc_bottom = 0; sh->i_delta_poc[0] = 0; sh->i_delta_poc[1] = 0; sh->i_redundant_pic_cnt = 0; h->mb.b_direct_auto_write = h->param.analyse.i_direct_mv_pred == X264_DIRECT_PRED_AUTO && h->param.i_bframe && ( h->param.rc.b_stat_write || !h->param.rc.b_stat_read ); if( !h->mb.b_direct_auto_read && sh->i_type == SLICE_TYPE_B ) { if( h->fref[1][0]->i_poc_l0ref0 == h->fref[0][0]->i_poc ) { if( h->mb.b_direct_auto_write ) sh->b_direct_spatial_mv_pred = ( h->stat.i_direct_score[1] > h->stat.i_direct_score[0] ); else sh->b_direct_spatial_mv_pred = ( param->analyse.i_direct_mv_pred == X264_DIRECT_PRED_SPATIAL ); } else { h->mb.b_direct_auto_write = 0; sh->b_direct_spatial_mv_pred = 1; } } /* else b_direct_spatial_mv_pred was read from the 2pass statsfile */ sh->b_num_ref_idx_override = 0; sh->i_num_ref_idx_l0_active = 1; sh->i_num_ref_idx_l1_active = 1; sh->b_ref_pic_list_reordering[0] = h->b_ref_reorder[0]; sh->b_ref_pic_list_reordering[1] = h->b_ref_reorder[1]; /* If the ref list isn't in the default order, construct reordering header */ for( int list = 0; list < 2; list++ ) { if( sh->b_ref_pic_list_reordering[list] ) { int pred_frame_num = i_frame; for( int i = 0; i < h->i_ref[list]; i++ ) { int diff = h->fref[list][i]->i_frame_num - pred_frame_num; sh->ref_pic_list_order[list][i].idc = ( diff > 0 ); sh->ref_pic_list_order[list][i].arg = (abs(diff) - 1) & ((1 << sps->i_log2_max_frame_num) - 1); pred_frame_num = h->fref[list][i]->i_frame_num; } } } sh->i_cabac_init_idc = param->i_cabac_init_idc; sh->i_qp = SPEC_QP(i_qp); sh->i_qp_delta = sh->i_qp - pps->i_pic_init_qp; sh->b_sp_for_swidth = 0; sh->i_qs_delta = 0; int deblock_thresh = i_qp + 2 * X264_MIN(param->i_deblocking_filter_alphac0, param->i_deblocking_filter_beta); /* If effective qp <= 15, deblocking would have no effect anyway */ if( param->b_deblocking_filter && (h->mb.b_variable_qp || 15 < deblock_thresh ) ) sh->i_disable_deblocking_filter_idc = param->b_sliced_threads ? 2 : 0; else sh->i_disable_deblocking_filter_idc = 1; sh->i_alpha_c0_offset = param->i_deblocking_filter_alphac0 << 1; sh->i_beta_offset = param->i_deblocking_filter_beta << 1; }

可以看出x264_slice_header_init()对x264_slice_header_t结构体的成员变量进行了赋值。

x264_slices_write()
编码数据（最关键的步骤）。其中调用了x264_slice_write()完成了编码的工作（注意“x264_slices_write()”和“x264_slice_write()”名字差了一个“s”）。

//真正的编码——编码1个图像帧 //注意“slice”后面有一个“s” //它其中又调用了一个x264_slice_write() //这一点要区分开 static void *x264_slices_write( x264_t *h ) { int i_slice_num = 0; int last_thread_mb = h->sh.i_last_mb; /* init stats */ memset( &h->stat.frame, 0, sizeof(h->stat.frame) ); h->mb.b_reencode_mb = 0; //循环每一个slice（一幅图像可以由多个Slice构成） while( h->sh.i_first_mb + SLICE_MBAFF*h->mb.i_mb_stride <= last_thread_mb ) { h->sh.i_last_mb = last_thread_mb; if( !i_slice_num || !x264_frame_new_slice( h, h->fdec ) ) { if( h->param.i_slice_max_mbs ) { if( SLICE_MBAFF ) { // convert first to mbaff form, add slice-max-mbs, then convert back to normal form int last_mbaff = 2*(h->sh.i_first_mb % h->mb.i_mb_width) + h->mb.i_mb_width*(h->sh.i_first_mb / h->mb.i_mb_width) + h->param.i_slice_max_mbs - 1; int last_x = (last_mbaff % (2*h->mb.i_mb_width))/2; int last_y = (last_mbaff / (2*h->mb.i_mb_width))*2 + 1; h->sh.i_last_mb = last_x + h->mb.i_mb_stride*last_y; } else { h->sh.i_last_mb = h->sh.i_first_mb + h->param.i_slice_max_mbs - 1; if( h->sh.i_last_mb < last_thread_mb && last_thread_mb - h->sh.i_last_mb < h->param.i_slice_min_mbs ) h->sh.i_last_mb = last_thread_mb - h->param.i_slice_min_mbs; } i_slice_num++; } else if( h->param.i_slice_count && !h->param.b_sliced_threads ) { int height = h->mb.i_mb_height >> PARAM_INTERLACED; int width = h->mb.i_mb_width << PARAM_INTERLACED; i_slice_num++; h->sh.i_last_mb = (height * i_slice_num + h->param.i_slice_count/2) / h->param.i_slice_count * width - 1; } } h->sh.i_last_mb = X264_MIN( h->sh.i_last_mb, last_thread_mb ); //真正的编码——编码1个Slice //x264_stack_align()应该是平台优化过程中内存对齐的工作 //实际上就是调用x264_slice_write() if( x264_stack_align( x264_slice_write, h ) ) goto fail; //注意这里对i_first_mb进行了赋值 h->sh.i_first_mb = h->sh.i_last_mb + 1; // if i_first_mb is not the last mb in a row then go to the next mb in MBAFF order if( SLICE_MBAFF && h->sh.i_first_mb % h->mb.i_mb_width ) h->sh.i_first_mb -= h->mb.i_mb_stride; } return (void *)0; fail: /* Tell other threads we're done, so they wouldn't wait for it */ if( h->param.b_sliced_threads ) x264_threadslice_cond_broadcast( h, 2 ); return (void *)-1; }

在这里需要注意，x264_slices_write()调用了x264_slice_write()。其中x264_slices_write()的单位为帧，而x264_slice_write()的单位为Slice。最常见的情况下一个帧里面只有一个Slice，但是也有可能一个帧里面有多个Slice。

x264_slice_write()
x264_slice_write()是完成编码工作的函数。该函数中包含了去块效应滤波，运动估计，宏块编码，熵编码等模块，它的调用结构大致如下图所示。

本文暂不分析x264_slice_write()函数。从下一篇文章开始将会对该函数进行详细的分析。

x264_encoder_frame_end()
x264_encoder_frame_end()用于在编码结束后做一些后续处理，例如封装NALU（加上起始码），释放一些中间变量，记录一些统计信息等。该函数的定义位于encoder\encoder.c，如下所示。

//结束的时候做一些处理，记录一些统计信息 //pp_nal：输出的NALU //pic_out：输出的重建帧 static int x264_encoder_frame_end( x264_t *h, x264_t *thread_current, x264_nal_t **pp_nal, int *pi_nal, x264_picture_t *pic_out ) { char psz_message[80]; if( !h->param.b_sliced_threads && h->b_thread_active ) { h->b_thread_active = 0; if( (intptr_t)x264_threadpool_wait( h->threadpool, h ) ) return -1; } if( !h->out.i_nal ) { pic_out->i_type = X264_TYPE_AUTO; return 0; } x264_emms(); /* generate buffering period sei and insert it into place */ if( h->i_thread_frames > 1 && h->fenc->b_keyframe && h->sps->vui.b_nal_hrd_parameters_present ) { x264_hrd_fullness( h ); x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE ); x264_sei_buffering_period_write( h, &h->out.bs ); if( x264_nal_end( h ) ) return -1; /* buffering period sei must follow AUD, SPS and PPS and precede all other SEIs */ int idx = 0; while( h->out.nal[idx].i_type == NAL_AUD || h->out.nal[idx].i_type == NAL_SPS || h->out.nal[idx].i_type == NAL_PPS ) idx++; x264_nal_t nal_tmp = h->out.nal[h->out.i_nal-1]; memmove( &h->out.nal[idx+1], &h->out.nal[idx], (h->out.i_nal-idx-1)*sizeof(x264_nal_t) ); h->out.nal[idx] = nal_tmp; } //封装一帧数据对应的NALU. //例如给NALU添加起始码0x00000001 int frame_size = x264_encoder_encapsulate_nals( h, 0 ); if( frame_size < 0 ) return -1; /* Set output picture properties */ //pic_out为x264_picture_t类型结构体。是libx264对外的结构体 //fenc,fdec是x264_frame_t类型结构体。是libx264的内部结构体 pic_out->i_type = h->fenc->i_type; pic_out->b_keyframe = h->fenc->b_keyframe; pic_out->i_pic_struct = h->fenc->i_pic_struct; pic_out->i_pts = h->fdec->i_pts; pic_out->i_dts = h->fdec->i_dts; if( pic_out->i_pts < pic_out->i_dts ) x264_log( h, X264_LOG_WARNING, "invalid DTS: PTS is less than DTS\n" ); pic_out->opaque = h->fenc->opaque; pic_out->img.i_csp = h->fdec->i_csp; #if HIGH_BIT_DEPTH pic_out->img.i_csp |= X264_CSP_HIGH_DEPTH; #endif pic_out->img.i_plane = h->fdec->i_plane; //图像数据 for( int i = 0; i < pic_out->img.i_plane; i++ ) { pic_out->img.i_stride[i] = h->fdec->i_stride[i] * sizeof(pixel); pic_out->img.plane[i] = (uint8_t*)h->fdec->plane[i]; } //回收用过的编码帧fenc x264_frame_push_unused( thread_current, h->fenc ); /* ---------------------- Update encoder state ------------------------- */ /* update rc */ int filler = 0; if( x264_ratecontrol_end( h, frame_size * 8, &filler ) < 0 ) return -1; pic_out->hrd_timing = h->fenc->hrd_timing; pic_out->prop.f_crf_avg = h->fdec->f_crf_avg; /* Filler in AVC-Intra mode is written as zero bytes to the last slice * We don't know the size of the last slice until encapsulation so we add filler to the encapsulated NAL */ if( h->param.i_avcintra_class ) { x264_t *h0 = h->thread[0]; int ret = x264_check_encapsulated_buffer( h, h0, h->out.i_nal, frame_size, frame_size + filler ); if( ret < 0 ) return -1; memset( h->out.nal[0].p_payload + frame_size, 0, filler ); h->out.nal[h->out.i_nal-1].i_payload += filler; h->out.nal[h->out.i_nal-1].i_padding = filler; frame_size += filler; } else { while( filler > 0 ) { int f, overhead; overhead = (FILLER_OVERHEAD - h->param.b_annexb); if( h->param.i_slice_max_size && filler > h->param.i_slice_max_size ) { int next_size = filler - h->param.i_slice_max_size; int overflow = X264_MAX( overhead - next_size, 0 ); f = h->param.i_slice_max_size - overhead - overflow; } else f = X264_MAX( 0, filler - overhead ); if( x264_bitstream_check_buffer_filler( h, f ) ) return -1; x264_nal_start( h, NAL_FILLER, NAL_PRIORITY_DISPOSABLE ); x264_filler_write( h, &h->out.bs, f ); if( x264_nal_end( h ) ) return -1; int total_size = x264_encoder_encapsulate_nals( h, h->out.i_nal-1 ); if( total_size < 0 ) return -1; frame_size += total_size; filler -= total_size; } } /* End bitstream, set output */ *pi_nal = h->out.i_nal; *pp_nal = h->out.nal; h->out.i_nal = 0; x264_noise_reduction_update( h ); /* ---------------------- Compute/Print statistics --------------------- */ x264_thread_sync_stat( h, h->thread[0] ); /* Slice stat */ //stat中存储了统计信息 //帧数+1 （根据类型） h->stat.i_frame_count[h->sh.i_type]++; //帧大小 h->stat.i_frame_size[h->sh.i_type] += frame_size; h->stat.f_frame_qp[h->sh.i_type] += h->fdec->f_qp_avg_aq; //统计MB个数，把不同类型的累加起来 for( int i = 0; i < X264_MBTYPE_MAX; i++ ) h->stat.i_mb_count[h->sh.i_type][i] += h->stat.frame.i_mb_count[i]; for( int i = 0; i < X264_PARTTYPE_MAX; i++ ) h->stat.i_mb_partition[h->sh.i_type][i] += h->stat.frame.i_mb_partition[i]; for( int i = 0; i < 2; i++ ) h->stat.i_mb_count_8x8dct[i] += h->stat.frame.i_mb_count_8x8dct[i]; for( int i = 0; i < 6; i++ ) h->stat.i_mb_cbp[i] += h->stat.frame.i_mb_cbp[i]; for( int i = 0; i < 4; i++ ) for( int j = 0; j < 13; j++ ) h->stat.i_mb_pred_mode[i][j] += h->stat.frame.i_mb_pred_mode[i][j]; if( h->sh.i_type != SLICE_TYPE_I ) for( int i_list = 0; i_list < 2; i_list++ ) for( int i = 0; i < X264_REF_MAX*2; i++ ) h->stat.i_mb_count_ref[h->sh.i_type][i_list][i] += h->stat.frame.i_mb_count_ref[i_list][i]; for( int i = 0; i < 3; i++ ) h->stat.i_mb_field[i] += h->stat.frame.i_mb_field[i]; if( h->sh.i_type == SLICE_TYPE_P && h->param.analyse.i_weighted_pred >= X264_WEIGHTP_SIMPLE ) { h->stat.i_wpred[0] += !!h->sh.weight[0][0].weightfn; h->stat.i_wpred[1] += !!h->sh.weight[0][1].weightfn || !!h->sh.weight[0][2].weightfn; } if( h->sh.i_type == SLICE_TYPE_B ) { h->stat.i_direct_frames[ h->sh.b_direct_spatial_mv_pred ] ++; if( h->mb.b_direct_auto_write ) { //FIXME somewhat arbitrary time constants if( h->stat.i_direct_score[0] + h->stat.i_direct_score[1] > h->mb.i_mb_count ) for( int i = 0; i < 2; i++ ) h->stat.i_direct_score[i] = h->stat.i_direct_score[i] * 9/10; for( int i = 0; i < 2; i++ ) h->stat.i_direct_score[i] += h->stat.frame.i_direct_score[i]; } } else h->stat.i_consecutive_bframes[h->fenc->i_bframes]++; psz_message[0] = '\0'; double dur = h->fenc->f_duration; h->stat.f_frame_duration[h->sh.i_type] += dur; //需要计算PSNR if( h->param.analyse.b_psnr ) { //SSD（Sum of Squared Difference）即差值的平方和 int64_t ssd[3] = { h->stat.frame.i_ssd[0], h->stat.frame.i_ssd[1], h->stat.frame.i_ssd[2], }; int luma_size = h->param.i_width * h->param.i_height; int chroma_size = CHROMA_SIZE( luma_size ); //SSD是已经在“滤波”环节计算过的 //SSD简单换算成PSNR，调用x264_psnr() pic_out->prop.f_psnr[0] = x264_psnr( ssd[0], luma_size ); pic_out->prop.f_psnr[1] = x264_psnr( ssd[1], chroma_size ); pic_out->prop.f_psnr[2] = x264_psnr( ssd[2], chroma_size ); //平均值 pic_out->prop.f_psnr_avg = x264_psnr( ssd[0] + ssd[1] + ssd[2], luma_size + chroma_size*2 ); //mean系列的需要累加 h->stat.f_ssd_global[h->sh.i_type] += dur * (ssd[0] + ssd[1] + ssd[2]); h->stat.f_psnr_average[h->sh.i_type] += dur * pic_out->prop.f_psnr_avg; h->stat.f_psnr_mean_y[h->sh.i_type] += dur * pic_out->prop.f_psnr[0]; h->stat.f_psnr_mean_u[h->sh.i_type] += dur * pic_out->prop.f_psnr[1]; h->stat.f_psnr_mean_v[h->sh.i_type] += dur * pic_out->prop.f_psnr[2]; snprintf( psz_message, 80, " PSNR Y:%5.2f U:%5.2f V:%5.2f", pic_out->prop.f_psnr[0], pic_out->prop.f_psnr[1], pic_out->prop.f_psnr[2] ); } //需要计算SSIM if( h->param.analyse.b_ssim ) { //SSIM是已经在“滤波”环节计算过的 pic_out->prop.f_ssim = h->stat.frame.f_ssim / h->stat.frame.i_ssim_cnt; //mean系列的需要累加 h->stat.f_ssim_mean_y[h->sh.i_type] += pic_out->prop.f_ssim * dur; snprintf( psz_message + strlen(psz_message), 80 - strlen(psz_message), " SSIM Y:%.5f", pic_out->prop.f_ssim ); } psz_message[79] = '\0'; //Debug时候输出 x264_log( h, X264_LOG_DEBUG, "frame=%4d QP=%.2f NAL=%d Slice:%c Poc:%-3d I:%-4d P:%-4d SKIP:%-4d size=%d bytes%s\n", h->i_frame, h->fdec->f_qp_avg_aq, h->i_nal_ref_idc, h->sh.i_type == SLICE_TYPE_I ? 'I' : (h->sh.i_type == SLICE_TYPE_P ? 'P' : 'B' ), h->fdec->i_poc, h->stat.frame.i_mb_count_i, h->stat.frame.i_mb_count_p, h->stat.frame.i_mb_count_skip, frame_size, psz_message ); // keep stats all in one place x264_thread_sync_stat( h->thread[0], h ); // for the use of the next frame x264_thread_sync_stat( thread_current, h ); #ifdef DEBUG_MB_TYPE { static const char mb_chars[] = { 'i', 'i', 'I', 'C', 'P', '8', 'S', 'D', '<', 'X', 'B', 'X', '>', 'B', 'B', 'B', 'B', '8', 'S' }; for( int mb_xy = 0; mb_xy < h->mb.i_mb_width * h->mb.i_mb_height; mb_xy++ ) { if( h->mb.type[mb_xy] < X264_MBTYPE_MAX && h->mb.type[mb_xy] >= 0 ) fprintf( stderr, "%c ", mb_chars[ h->mb.type[mb_xy] ] ); else fprintf( stderr, "? " ); if( (mb_xy+1) % h->mb.i_mb_width == 0 ) fprintf( stderr, "\n" ); } } #endif /* Remove duplicates, must be done near the end as breaks h->fref0 array * by freeing some of its pointers. */ for( int i = 0; i < h->i_ref[0]; i++ ) if( h->fref[0][i] && h->fref[0][i]->b_duplicate ) { x264_frame_push_blank_unused( h, h->fref[0][i] ); h->fref[0][i] = 0; } if( h->param.psz_dump_yuv ) x264_frame_dump( h ); x264_emms(); return frame_size; }

从源代码可以看出，x264_encoder_frame_end()中大部分代码用于把统计信息记录到x264_t的stat中。此外做了一些后续处理：调用了x264_encoder_encapsulate_nals()封装NALU（添加起始码），调用x264_frame_push_unused()将fenc重新放回frames.unused[]队列，并且调用x264_ratecontrol_end()结束码率控制。

x264_encoder_encapsulate_nals()
x264_encoder_encapsulate_nals()用于封装一帧数据对应的NALU，其代码如下所示。

//封装一帧数据对应的NALU. //例如给NALU添加起始码0x00000001 static int x264_encoder_encapsulate_nals( x264_t *h, int start ) { x264_t *h0 = h->thread[0]; int nal_size = 0, previous_nal_size = 0; if( h->param.nalu_process ) { for( int i = start; i < h->out.i_nal; i++ ) nal_size += h->out.nal[i].i_payload; return nal_size; } for( int i = 0; i < start; i++ ) previous_nal_size += h->out.nal[i].i_payload; for( int i = start; i < h->out.i_nal; i++ ) nal_size += h->out.nal[i].i_payload; /* Worst-case NAL unit escaping: reallocate the buffer if it's too small. */ int necessary_size = previous_nal_size + nal_size * 3/2 + h->out.i_nal * 4 + 4 + 64; for( int i = start; i < h->out.i_nal; i++ ) necessary_size += h->out.nal[i].i_padding; if( x264_check_encapsulated_buffer( h, h0, start, previous_nal_size, necessary_size ) ) return -1; uint8_t *nal_buffer = h0->nal_buffer + previous_nal_size; //一个一个NALU处理 for( int i = start; i < h->out.i_nal; i++ ) { int old_payload_len = h->out.nal[i].i_payload; h->out.nal[i].b_long_startcode = !i || h->out.nal[i].i_type == NAL_SPS || h->out.nal[i].i_type == NAL_PPS || h->param.i_avcintra_class; //添加起始码 x264_nal_encode( h, nal_buffer, &h->out.nal[i] ); nal_buffer += h->out.nal[i].i_payload; if( h->param.i_avcintra_class ) { h->out.nal[i].i_padding -= h->out.nal[i].i_payload - (old_payload_len + NALU_OVERHEAD); if( h->out.nal[i].i_padding > 0 ) { memset( nal_buffer, 0, h->out.nal[i].i_padding ); nal_buffer += h->out.nal[i].i_padding; h->out.nal[i].i_payload += h->out.nal[i].i_padding; } h->out.nal[i].i_padding = X264_MAX( h->out.nal[i].i_padding, 0 ); } } x264_emms(); return nal_buffer - (h0->nal_buffer + previous_nal_size); }

从源代码中可以看出，x264_encoder_encapsulate_nals()调用了另外一个函数x264_nal_encode()逐个给一帧数据中的各个NALU添加起始码以及NALU Header等。

[b]x264_nal_encode()

x264_nal_encode()用于给NALU添加起始码以及NALU Header等。该函数的定义位于common\bitstream.c，如下所示。

/****************************************************************************
* x264_nal_encode:
****************************************************************************/
//添加起始码
void x264_nal_encode( x264_t *h, uint8_t *dst, x264_nal_t *nal )
{
uint8_t *src = nal->p_payload;
uint8_t *end = nal->p_payload + nal->i_payload;
uint8_t *orig_dst = dst;
//起始码 ============================================
//annexb格式，起始码为0x00000001
if( h->param.b_annexb )
{
if( nal->b_long_startcode )
*dst++ = 0x00;
*dst++ = 0x00;
*dst++ = 0x00;
*dst++ = 0x01;
}
else /* save room for size later */
dst += 4;//mp4格式

//NALU Header =======================================
/* nal header */
*dst++ = ( 0x00 << 7 ) | ( nal->i_ref_idc << 5 ) | nal->i_type;

dst = h->bsf.nal_escape( dst, src, end );
int size = (dst - orig_dst) - 4;

/* Write the size header for mp4/etc */
//重新回到起始码的位置，写入mp4格式的起始码（size大小，不含起始码）
if( !h->param.b_annexb )
{
/* Size doesn't include the size of the header we're writing now. */
orig_dst[0] = size>>24;
orig_dst[1] = size>>16;
orig_dst[2] = size>> 8;
orig_dst[3] = size>> 0;
}
//NALU负载大小，包含起始码
nal->i_payload = size+4;
nal->p_payload = orig_dst;
x264_emms();
}

从源代码可以看出，x264_nal_encode()给NALU数据添加了起始码以及NALU Header。在这里简单总结一下起始码的添加过程。

H.264码流有两种格式：

（1）annexb模式（传统模式）。这种模式下每个NALU包含起始码0x00000001；而且SPS、PPS存储在ES码流中。常见的H.264裸流就是属于这种格式。

（2）mp4模式。这种模式下每个NALU不包含起始码，原本存储起始码前4个字节存储的是这个NALU的长度（不包含前4字节）；而且SPS、PPS被单独放在容器的其他位置上。这种H.264一般存储在某些容器中，例如MP4中。
从源代码中可以看出，x264_nal_encode()根据H.264码流格式的不同分成两种情况给NALU添加起始码：

（1）annexb模式下，在每个NALU前面添加0x00000001。

（2）mp4模式下，先计算NALU的长度（不包含前4字节），再将长度信息写入NALU前面的4个字节

至此有关编码器主干部分有关x264_encoder_encode()的源代码就分析完了。从下一篇文章开始将会开始分析编码Slice的函数——x264_slice_write()。

雷霄骅
leixiaohua1020@126.com http://blog.csdn.net/leixiaohua1020

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