FFmpeg: cur_dts is invalid

摘要: cur_dts is invalid

声明：转帖时请注明出处

FFmpeg 版本3.0
调用ffmpeg执行转码时，发现会有如下打印信息：

cur_dts is invalid (this is harmless if it occurs once at the start per stream)

ffmpeg.c对应代码如下：

[code=language-cpp]/**
* Select the output stream to process.
*
* @return  selected output stream, or NULL if none available
*/
static OutputStream *choose_output(void)
{
int i;
int64_t opts_min = INT64_MAX;
OutputStream *ost_min = NULL;

for (i = 0; i < nb_output_streams; i++) {
OutputStream *ost = output_streams[i];
int64_t opts = ost->st->cur_dts == AV_NOPTS_VALUE ? INT64_MIN :
av_rescale_q(ost->st->cur_dts, ost->st->time_base,
AV_TIME_BASE_Q);
if (ost->st->cur_dts == AV_NOPTS_VALUE)
av_log(NULL, AV_LOG_DEBUG, "cur_dts is invalid (this is harmless if it occurs once at the start per stream)\n");

if (!ost->finished && opts < opts_min) {
opts_min = opts;
ost_min  = ost->unavailable ? NULL : ost;
}
}
return ost_min;
}

h264 encoder.c 初始化代码如下：

[code=language-cs]    /* Init frames. */
if( h->param.i_bframe_adaptive == X264_B_ADAPT_TRELLIS && !h->param.rc.b_stat_read )
h->frames.i_delay = X264_MAX(h->param.i_bframe,3)*4;
else
h->frames.i_delay = h->param.i_bframe;
if( h->param.rc.b_mb_tree || h->param.rc.i_vbv_buffer_size )
h->frames.i_delay = X264_MAX( h->frames.i_delay, h->param.rc.i_lookahead );
i_slicetype_length = h->frames.i_delay;
h->frames.i_delay += h->i_thread_frames - 1;
h->frames.i_delay += h->param.i_sync_lookahead;
h->frames.i_delay += h->param.b_vfr_input;

等待填满编码缓冲区代码如下：

[code=language-cpp]    /* ------------------- Setup new frame from picture -------------------- */
if( pic_in != NULL )
{
/* 1: Copy the picture to a frame and move it to a buffer */
x264_frame_t *fenc = x264_frame_pop_unused( h, 0 );
if( !fenc )
return -1;

if( x264_frame_copy_picture( h, fenc, pic_in ) < 0 )
return -1;

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 );

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 );

if( h->frames.b_have_lowres )
x264_frame_init_lowres( h, fenc );

/* 2: Place the frame into the queue for its slice type decision */
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
{
/* 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 );
}

以视频h264编码为例，该打印的数量与输出编码帧的时间有关：

bframes ： consecutive B-frames before this P-frame

i_lookahead： Number of frames for frametype lookahead

i_thread_frames：/* Number of different frames being encoded by threads;
* 1 when sliced-threads is on. */

i_sync_lookahead; /* threaded lookahead buffer */

b_vfr_input; /* VFR input. If 1, use timebase and timestamps for ratecontrol purposes.
* If 0, use fps only. */

ffmpeg命令行：

./ffmpeg -i test_2.flv -vcodec libx264 -r 10 -report -y -f flv test_2out.flv

x264 encoder.c中添加打印语句如下：

[code=language-cpp]    /* Init frames. */
if( h->param.i_bframe_adaptive == X264_B_ADAPT_TRELLIS && !h->param.rc.b_stat_read )
h->frames.i_delay = X264_MAX(h->param.i_bframe,3)*4;
else
h->frames.i_delay = h->param.i_bframe;
x264_log( h, X264_LOG_DEBUG,"X264 init1 delay:%d\n",h->frames.i_delay);
if( h->param.rc.b_mb_tree || h->param.rc.i_vbv_buffer_size )
h->frames.i_delay = X264_MAX( h->frames.i_delay, h->param.rc.i_lookahead );
x264_log( h, X264_LOG_DEBUG,"X264 init2 delay:%d\n",h->frames.i_delay);
i_slicetype_length = h->frames.i_delay;
h->frames.i_delay += h->i_thread_frames - 1;
x264_log( h, X264_LOG_DEBUG,"X264 init3 delay:%d\n",h->frames.i_delay);
h->frames.i_delay += h->param.i_sync_lookahead;
x264_log( h, X264_LOG_DEBUG,"X264 init4 delay:%d\n",h->frames.i_delay);
h->frames.i_delay += h->param.b_vfr_input;
x264_log( h, X264_LOG_DEBUG,"X264 init5 delay:%d\n",h->frames.i_delay);

打印日志：

[code=plain][libx264 @ 0x335a580] X264 init1 delay:3
[libx264 @ 0x335a580] X264 init2 delay:40
[libx264 @ 0x335a580] X264 init3 delay:40
[libx264 @ 0x335a580] X264 init4 delay:40
[libx264 @ 0x335a580] X264 init5 delay:41

总结：

cur_dts is invalid (this is harmless if it occurs once at the start per stream) 打印信息与编码输出帧的延时有关，其中最主要与i_lookahead值有关。

当编码器有帧输出时，则不会出现该打印信息。

如下图所示，解码41帧后，第42帧开始进行编码。

[code=language-cpp][libx264 @ 0x335a580] x264 frame info........
[libx264 @ 0x335a580] x264 frame encoder info........
[libx264 @ 0x335a580] X264 input frame:41, delay frame:41, thread frame:1
[libx264 @ 0x335a580] x264 frame encoder finish........
choose_output, OutputStream stream cur_dts:0 ...
cur_dts is invalid (this is harmless if it occurs once at the start per stream)
choose_output, OutputStream stream cur_dts:3864 ...
OutputStream filter is true ...
process input, file index0, ...
choose_output, OutputStream stream cur_dts:0 ...
cur_dts is invalid (this is harmless if it occurs once at the start per stream)
choose_output, OutputStream stream cur_dts:3890 ...
OutputStream filter is true ...
process input, file index0, ...
choose_output, OutputStream stream cur_dts:0 ...
cur_dts is invalid (this is harmless if it occurs once at the start per stream)
choose_output, OutputStream stream cur_dts:3917 ...
OutputStream filter is true ...
process input, file index0, ...
choose_output, OutputStream stream cur_dts:0 ...
cur_dts is invalid (this is harmless if it occurs once at the start per stream)
choose_output, OutputStream stream cur_dts:3943 ...
OutputStream filter is true ...
process input, file index0, ...
[h264 @ 0x3355260] decoding video .......
[libx264 @ 0x335a580] x264 frame info........
[libx264 @ 0x335a580] x264 frame encoder info........
[libx264 @ 0x335a580] X264 input frame:42, delay frame:41, thread frame:1
[libx264 @ 0x335a580] frame=   0 QP=2.40 NAL=3 Slice:I Poc:0   I:1064 P:0    SKIP:0    size=1086 bytes
[libx264 @ 0x335a580] x264 frame encoder finish........
[flv @ 0x3263460] flv enc type:0, dts:0 pts:200
choose_output, OutputStream stream cur_dts:-100 ..

注释：

libx264库在添加打印后，需要进行编译和安装，即make && make install

此外，ffmpeg也需要配置，编译和安装，才能使打印信息生效。