[原]零基础学习视频解码之seek

现在，我们要添加一些功能，当你看不能倒带的电影，是不是很烦？ 那么函数av_seek_frame功能看起来是多么赏心悦目。

我们将让左，右箭头来回走在影片中通过一个小的向上和向下箭头很多，其中“三多一少”是10秒，“很多”为60秒。因此，我们需要设置我们的主循环，用来捕获击键。然而，当我们得到一个按键，就不能直接称之为函数av_seek_frame。我们所要做的是在我们的主解码循环中，decode_thread循环做相应的处理。

为了检测按键，我们先来看看，看看我们得到了一个SDL_KEYDOWN事件。然后我们检查，看看哪个键得到使用event.key.keysym.sym。一旦我们知道我们要seek哪一种方式，我们通过增加增量，从我们的新get_master_clock函数值计算新的时间。接着我们调用stream_seek函数来设置seek_pos等值。我们新的时间转换为avcodec中的内部时间戳单元。回想一下，时间戳在流测量中的帧，而不是秒，于是秒=帧*time_base（fps）。 avcodec中默认为1,000,000 fps的值（这样的2秒的POS将是2000000时间戳）。

现在，让我们去到我们的decode_thread，我们将实际执行我们的seek。你会发现在我们已经标志着一个区域的源文件“seek的东西放在这里”，好了，我们打算把它放在那里了。
seek的函数av_seek_frame，该函数将seek到给它的时间戳。时间戳的单位是传递函数的流的基本time_base。但是，你不必把它传递一个流（通过传递值-1表示）。如果你这样做，那么time_base将是avcodec中的内部时间戳单位，或者1000000fps。这就是为什么当我们设置seek_pos乘AV_TIME_BASE。

av_rescale_q（A，B，C）是将重新调整时间戳从一个基地到另一个函数。它基本上是计算A * B/ C，但这个功能是必需的，因为计算可能溢出。 AV_TIME_BASE_Q是AV_TIME_BASE的小数版本。他们是完全不同的：AV_TIME_BASE* time_in_seconds= avcodec_timestamp和AV_TIME_BASE_Q* avcodec_timestamp= time_in_seconds（但要注意，AV_TIME_BASE_Q实际上是一个AVRational对象，所以你必须要使用特殊的q函数在avcodec中处理它）。

是的，但我们没有完成很呢。请记住，我们有一个队列设置了累积的数据包。现在，我们在不同的地方，我们要刷新的队列不是要去seek！不仅如此，avcodec中它自己内部的各缓冲器的需要由每个线程去刷新。

要做到这一点，我们需要先写一个函数来清除我们的数据包队列。然后，我们需要有指示音频和视频线，他们需要刷新avcodec中的内部缓冲器的一些方式。我们可以通过把一种特殊的数据包队列后，而当他们发现了特殊的包，他们就会刷新自己的缓冲区。

/*
============================================================================
Name        : VideoDecodeTutorial7_1.c
Author      : clarck
Version     :
Copyright   : Your copyright notice
Description : Hello World in C, Ansi-style
============================================================================
*/
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavformat/avio.h>
#include <libswscale/swscale.h>
#include <libavutil/avstring.h>
#include <libavutil/mathematics.h>
#include <libavutil/time.h>

#include <SDL/SDL.h>
#include <SDL/SDL_thread.h>

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#include <stdio.h>
#include <math.h>

#define SDL_AUDIO_BUFFER_SIZE 1024

#define MAX_AUDIOQ_SIZE (5 * 16 * 1024)
#define MAX_VIDEOQ_SIZE (5 * 256 * 1024)

#define AV_SYNC_THRESHOLD 0.01
#define AV_NOSYNC_THRESHOLD 10.0

#define SAMPLE_CORRECTION_PERCENT_MAX 10
#define AUDIO_DIFF_AVG_NB 20

#define FF_ALLOC_EVENT   (SDL_USEREVENT)
#define FF_REFRESH_EVENT (SDL_USEREVENT + 1)
#define FF_QUIT_EVENT (SDL_USEREVENT + 2)

#define VIDEO_PICTURE_QUEUE_SIZE 1

#define DEFAULT_AV_SYNC_TYPE AV_SYNC_VIDEO_MASTER
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
AVPacketList *first_pkt, *last_pkt;
int nb_packets;
int size;
SDL_mutex *mutex;
SDL_cond *cond;
} PacketQueue;

typedef struct VideoPicture {
SDL_Overlay *bmp;
int width, height; /* source height & width */
int allocated;
double pts;
} VideoPicture;

typedef struct VideoState {

AVFormatContext *pFormatCtx;
int videoStream, audioStream;

int av_sync_type;
double external_clock; /* external clock base */
int64_t external_clock_time;

int seek_req;
int seek_flags;
int64_t seek_pos;

double audio_clock;
AVStream *audio_st;
PacketQueue audioq;
uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];
unsigned int audio_buf_size;
unsigned int audio_buf_index;
AVPacket audio_pkt;
uint8_t *audio_pkt_data;
int audio_pkt_size;
AVFrame audio_frame;
AVStream *video_st;
PacketQueue videoq;
int audio_hw_buf_size;
double audio_diff_cum; /* used for AV difference average computation */
double audio_diff_avg_coef;
double audio_diff_threshold;
int audio_diff_avg_count;
double frame_timer;
double frame_last_pts;
double frame_last_delay;

double video_current_pts; ///<current displayed pts (different from video_clock if frame fifos are used)
int64_t video_current_pts_time; ///<time (av_gettime) at which we updated video_current_pts - used to have running video pts

double video_clock; ///<pts of last decoded frame / predicted pts of next decoded frame

VideoPicture pictq[VIDEO_PICTURE_QUEUE_SIZE];
int pictq_size, pictq_rindex, pictq_windex;
SDL_mutex *pictq_mutex;
SDL_cond *pictq_cond;

SDL_Thread *parse_tid;
SDL_Thread *video_tid;

AVIOContext *io_ctx;
struct SwsContext *sws_ctx;

char filename[1024];
int quit;
} VideoState;

enum {
AV_SYNC_AUDIO_MASTER, AV_SYNC_VIDEO_MASTER, AV_SYNC_EXTERNAL_MASTER,
};

SDL_Surface *screen;

/* Since we only have one decoding thread, the Big Struct
can be global in case we need it. */
VideoState *global_video_state;

AVPacket flush_pkt;

void packet_queue_init(PacketQueue *q) {
memset(q, 0, sizeof(PacketQueue));
q->mutex = SDL_CreateMutex();
q->cond = SDL_CreateCond();
}
int packet_queue_put(PacketQueue *q, AVPacket *pkt) {

AVPacketList *pkt1;
if (pkt != &flush_pkt && av_dup_packet(pkt) < 0) {
return -1;
}
pkt1 = av_malloc(sizeof(AVPacketList));
if (!pkt1)
return -1;
pkt1->pkt = *pkt;
pkt1->next = NULL;

SDL_LockMutex(q->mutex);

if (!q->last_pkt)
q->first_pkt = pkt1;
else
q->last_pkt->next = pkt1;
q->last_pkt = pkt1;
q->nb_packets++;
q->size += pkt1->pkt.size;
SDL_CondSignal(q->cond);

SDL_UnlockMutex(q->mutex);
return 0;
}
static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {
AVPacketList *pkt1;
int ret;

SDL_LockMutex(q->mutex);

for (;;) {

if (global_video_state->quit) {
ret = -1;
break;
}

pkt1 = q->first_pkt;
if (pkt1) {
q->first_pkt = pkt1->next;
if (!q->first_pkt)
q->last_pkt = NULL;
q->nb_packets--;
q->size -= pkt1->pkt.size;
*pkt = pkt1->pkt;
av_free(pkt1);
ret = 1;
break;
} else if (!block) {
ret = 0;
break;
} else {
SDL_CondWait(q->cond, q->mutex);
}
}
SDL_UnlockMutex(q->mutex);
return ret;
}

static void packet_queue_flush(PacketQueue *q) {
AVPacketList *pkt, *pkt1;

SDL_LockMutex(q->mutex);
for (pkt = q->first_pkt; pkt != NULL; pkt = pkt1) {
pkt1 = pkt->next;
av_free_packet(&pkt->pkt);
av_freep(&pkt);
}
q->last_pkt = NULL;
q->first_pkt = NULL;
q->nb_packets = 0;
q->size = 0;
SDL_UnlockMutex(q->mutex);
}

double get_audio_clock(VideoState *is) {
double pts;
int hw_buf_size, bytes_per_sec, n;

pts = is->audio_clock; /* maintained in the audio thread */
hw_buf_size = is->audio_buf_size - is->audio_buf_index;
bytes_per_sec = 0;
n = is->audio_st->codec->channels * 2;
if (is->audio_st) {
bytes_per_sec = is->audio_st->codec->sample_rate * n;
}
if (bytes_per_sec) {
pts -= (double) hw_buf_size / bytes_per_sec;
}
return pts;
}

double get_video_clock(VideoState *is) {
double delta;

delta = (av_gettime() - is->video_current_pts_time) / 1000000.0;
return is->video_current_pts + delta;
}
double get_external_clock(VideoState *is) {
return av_gettime() / 1000000.0;
}

double get_master_clock(VideoState *is) {
if (is->av_sync_type == AV_SYNC_VIDEO_MASTER) {
return get_video_clock(is);
} else if (is->av_sync_type == AV_SYNC_AUDIO_MASTER) {
return get_audio_clock(is);
} else {
return get_external_clock(is);
}
}
/* Add or subtract samples to get a better sync, return new
audio buffer size */
int synchronize_audio(VideoState *is, short *samples, int samples_size,
double pts) {
int n;
double ref_clock;

n = 2 * is->audio_st->codec->channels;

if (is->av_sync_type != AV_SYNC_AUDIO_MASTER) {
double diff, avg_diff;
int wanted_size, min_size, max_size;
//int nb_samples;

ref_clock = get_master_clock(is);
diff = get_audio_clock(is) - ref_clock;

if (diff < AV_NOSYNC_THRESHOLD) {
// accumulate the diffs
is->audio_diff_cum = diff
+ is->audio_diff_avg_coef * is->audio_diff_cum;
if (is->audio_diff_avg_count < AUDIO_DIFF_AVG_NB) {
is->audio_diff_avg_count++;
} else {
avg_diff = is->audio_diff_cum * (1.0 - is->audio_diff_avg_coef);
if (fabs(avg_diff) >= is->audio_diff_threshold) {
wanted_size = samples_size
+ ((int) (diff * is->audio_st->codec->sample_rate)
* n);
min_size = samples_size
* ((100 - SAMPLE_CORRECTION_PERCENT_MAX) / 100);
max_size = samples_size
* ((100 + SAMPLE_CORRECTION_PERCENT_MAX) / 100);
if (wanted_size < min_size) {
wanted_size = min_size;
} else if (wanted_size > max_size) {
wanted_size = max_size;
}
if (wanted_size < samples_size) {
/* remove samples */
samples_size = wanted_size;
} else if (wanted_size > samples_size) {
uint8_t *samples_end, *q;
int nb;

/* add samples by copying final sample*/
nb = (samples_size - wanted_size);
samples_end = (uint8_t *) samples + samples_size - n;
q = samples_end + n;
while (nb > 0) {
memcpy(q, samples_end, n);
q += n;
nb -= n;
}
samples_size = wanted_size;
}
}
}
} else {
/* difference is TOO big; reset diff stuff */
is->audio_diff_avg_count = 0;
is->audio_diff_cum = 0;
}
}
return samples_size;
}

int audio_decode_frame(VideoState *is, double *pts_ptr) {

int len1, data_size = 0, n;
AVPacket *pkt = &is->audio_pkt;
double pts;

for (;;) {
while (is->audio_pkt_size > 0) {
int got_frame = 0;
len1 = avcodec_decode_audio4(is->audio_st->codec, &is->audio_frame,
&got_frame, pkt);
if (len1 < 0) {
/* if error, skip frame */
is->audio_pkt_size = 0;
break;
}

if (got_frame) {
data_size = is->audio_frame.linesize[0];
/*av_samples_get_buffer_size(NULL,
is->audio_st->codec->channels,
is->audio_frame.nb_samples,
is->audio_st->codec->sample_fmt, 1);*/
memcpy(is->audio_buf, is->audio_frame.data[0], data_size);
}

is->audio_pkt_data += len1;
is->audio_pkt_size -= len1;
if (data_size <= 0) {
/* No data yet, get more frames */
continue;
}

pts = is->audio_clock;
*pts_ptr = pts;
n = 2 * is->audio_st->codec->channels;
is->audio_clock += (double) data_size
/ (double) (n * is->audio_st->codec->sample_rate);

/* We have data, return it and come back for more later */
return data_size;
}
if (pkt->data)
av_free_packet(pkt);

if (is->quit) {
return -1;
}
/* next packet */
if (packet_queue_get(&is->audioq, pkt, 1) < 0) {
return -1;
}

if (pkt->data == flush_pkt.data) {
avcodec_flush_buffers(is->audio_st->codec);
continue;
}

is->audio_pkt_data = pkt->data;
is->audio_pkt_size = pkt->size;

/* if update, update the audio clock w/pts */
if (pkt->pts != AV_NOPTS_VALUE) {
is->audio_clock = av_q2d(is->audio_st->time_base) * pkt->pts;
}
}

return 0;
}

void audio_callback(void *userdata, Uint8 *stream, int len) {

VideoState *is = (VideoState *) userdata;
int len1, audio_size;
double pts;

while (len > 0) {
if (is->audio_buf_index >= is->audio_buf_size) {
/* We have already sent all our data; get more */
audio_size = audio_decode_frame(is, &pts);
if (audio_size < 0) {
/* If error, output silence */
is->audio_buf_size = 1024;
memset(is->audio_buf, 0, is->audio_buf_size);
} else {
audio_size = synchronize_audio(is, (int16_t *) is->audio_buf,
audio_size, pts);
is->audio_buf_size = audio_size;
}
is->audio_buf_index = 0;
}
len1 = is->audio_buf_size - is->audio_buf_index;
if (len1 > len)
len1 = len;
memcpy(stream, (uint8_t *) is->audio_buf + is->audio_buf_index, len1);
len -= len1;
stream += len1;
is->audio_buf_index += len1;
}
}

static Uint32 sdl_refresh_timer_cb(Uint32 interval, void *opaque) {
SDL_Event event;
event.type = FF_REFRESH_EVENT;
event.user.data1 = opaque;
SDL_PushEvent(&event);
return 0; /* 0 means stop timer */
}

/* schedule a video refresh in 'delay' ms */
static void schedule_refresh(VideoState *is, int delay) {
SDL_AddTimer(delay, sdl_refresh_timer_cb, is);
}

void video_display(VideoState *is) {

SDL_Rect rect;
VideoPicture *vp;
float aspect_ratio;
int w, h, x, y;

vp = &is->pictq[is->pictq_rindex];
if (vp->bmp) {
if (is->video_st->codec->sample_aspect_ratio.num == 0) {
aspect_ratio = 0;
} else {
aspect_ratio = av_q2d(is->video_st->codec->sample_aspect_ratio)
* is->video_st->codec->width / is->video_st->codec->height;
}
if (aspect_ratio <= 0.0) {
aspect_ratio = (float) is->video_st->codec->width
/ (float) is->video_st->codec->height;
}
h = screen->h;
w = ((int) rint(h * aspect_ratio)) & -3;
if (w > screen->w) {
w = screen->w;
h = ((int) rint(w / aspect_ratio)) & -3;
}
x = (screen->w - w) / 2;
y = (screen->h - h) / 2;

rect.x = x;
rect.y = y;
rect.w = w;
rect.h = h;
SDL_DisplayYUVOverlay(vp->bmp, &rect);
}
}

void video_refresh_timer(void *userdata) {

VideoState *is = (VideoState *) userdata;
VideoPicture *vp;
double actual_delay, delay, sync_threshold, ref_clock, diff;

if (is->video_st) {
if (is->pictq_size == 0) {
schedule_refresh(is, 1);
} else {

vp = &is->pictq[is->pictq_rindex];

is->video_current_pts = vp->pts;
is->video_current_pts_time = av_gettime();

delay = vp->pts - is->frame_last_pts; /* the pts from last time */
if (delay <= 0 || delay >= 1.0) {
/* if incorrect delay, use previous one */
delay = is->frame_last_delay;
}
/* save for next time */
is->frame_last_delay = delay;
is->frame_last_pts = vp->pts;

/* update delay to sync to audio */
ref_clock = get_audio_clock(is);
diff = vp->pts - ref_clock;

/* update delay to sync to audio if not master source */
if (is->av_sync_type != AV_SYNC_VIDEO_MASTER) {
ref_clock = get_master_clock(is);
diff = vp->pts - ref_clock;

/* Skip or repeat the frame. Take delay into account
FFPlay still doesn't "know if this is the best guess." */
sync_threshold =
(delay > AV_SYNC_THRESHOLD) ? delay : AV_SYNC_THRESHOLD;
if (fabs(diff) < AV_NOSYNC_THRESHOLD) {
if (diff <= -sync_threshold) {
delay = 0;
} else if (diff >= sync_threshold) {
delay = 2 * delay;
}
}
}
is->frame_timer += delay;
/* computer the REAL delay */
actual_delay = is->frame_timer - (av_gettime() / 1000000.0);
if (actual_delay < 0.010) {
/* Really it should skip the picture instead */
actual_delay = 0.010;
}
schedule_refresh(is, (int) (actual_delay * 1000 + 0.5));

/* show the picture! */
video_display(is);

/* update queue for next picture! */
if (++is->pictq_rindex == VIDEO_PICTURE_QUEUE_SIZE) {
is->pictq_rindex = 0;
}
SDL_LockMutex(is->pictq_mutex);
is->pictq_size--;
SDL_CondSignal(is->pictq_cond);
SDL_UnlockMutex(is->pictq_mutex);
}
} else {
schedule_refresh(is, 100);
}
}

void alloc_picture(void *userdata) {

VideoState *is = (VideoState *) userdata;
VideoPicture *vp;

vp = &is->pictq[is->pictq_windex];
if (vp->bmp) {
// we already have one make another, bigger/smaller
SDL_FreeYUVOverlay(vp->bmp);
}
// Allocate a place to put our YUV image on that screen
vp->bmp = SDL_CreateYUVOverlay(is->video_st->codec->width,
is->video_st->codec->height, SDL_YV12_OVERLAY, screen);
vp->width = is->video_st->codec->width;
vp->height = is->video_st->codec->height;

SDL_LockMutex(is->pictq_mutex);
vp->allocated = 1;
SDL_CondSignal(is->pictq_cond);
SDL_UnlockMutex(is->pictq_mutex);

}

int queue_picture(VideoState *is, AVFrame *pFrame, double pts) {

VideoPicture *vp;
//int dst_pix_fmt;
AVPicture pict;

/* wait until we have space for a new pic */
SDL_LockMutex(is->pictq_mutex);
while (is->pictq_size >= VIDEO_PICTURE_QUEUE_SIZE && !is->quit) {
SDL_CondWait(is->pictq_cond, is->pictq_mutex);
}
SDL_UnlockMutex(is->pictq_mutex);

if (is->quit)
return -1;

// windex is set to 0 initially
vp = &is->pictq[is->pictq_windex];

/* allocate or resize the buffer! */
if (!vp->bmp || vp->width != is->video_st->codec->width
|| vp->height != is->video_st->codec->height) {
SDL_Event event;

vp->allocated = 0;
/* we have to do it in the main thread */
event.type = FF_ALLOC_EVENT;
event.user.data1 = is;
SDL_PushEvent(&event);

/* wait until we have a picture allocated */
SDL_LockMutex(is->pictq_mutex);
while (!vp->allocated && !is->quit) {
SDL_CondWait(is->pictq_cond, is->pictq_mutex);
}
SDL_UnlockMutex(is->pictq_mutex);
if (is->quit) {
return -1;
}
}
/* We have a place to put our picture on the queue */
/* If we are skipping a frame, do we set this to null
but still return vp->allocated = 1? */

if (vp->bmp) {

SDL_LockYUVOverlay(vp->bmp);

//dst_pix_fmt = PIX_FMT_YUV420P;
/* point pict at the queue */

pict.data[0] = vp->bmp->pixels[0];
pict.data[1] = vp->bmp->pixels[2];
pict.data[2] = vp->bmp->pixels[1];

pict.linesize[0] = vp->bmp->pitches[0];
pict.linesize[1] = vp->bmp->pitches[2];
pict.linesize[2] = vp->bmp->pitches[1];

// Convert the image into YUV format that SDL uses
sws_scale(is->sws_ctx, (const uint8_t * const *) pFrame->data,
pFrame->linesize, 0, is->video_st->codec->height, pict.data,
pict.linesize);

SDL_UnlockYUVOverlay(vp->bmp);
vp->pts = pts;

/* now we inform our display thread that we have a pic ready */
if (++is->pictq_windex == VIDEO_PICTURE_QUEUE_SIZE) {
is->pictq_windex = 0;
}
SDL_LockMutex(is->pictq_mutex);
is->pictq_size++;
SDL_UnlockMutex(is->pictq_mutex);
}
return 0;
}

double synchronize_video(VideoState *is, AVFrame *src_frame, double pts) {

double frame_delay;

if (pts != 0) {
/* if we have pts, set video clock to it */
is->video_clock = pts;
} else {
/* if we aren't given a pts, set it to the clock */
pts = is->video_clock;
}
/* update the video clock */
frame_delay = av_q2d(is->video_st->codec->time_base);
/* if we are repeating a frame, adjust clock accordingly */
frame_delay += src_frame->repeat_pict * (frame_delay * 0.5);
is->video_clock += frame_delay;
return pts;
}
uint64_t global_video_pkt_pts = AV_NOPTS_VALUE;

/* These are called whenever we allocate a frame
* buffer. We use this to store the global_pts in
* a frame at the time it is allocated.
*/
int our_get_buffer(struct AVCodecContext *c, AVFrame *pic) {
int ret = avcodec_default_get_buffer(c, pic);
uint64_t *pts = av_malloc(sizeof(uint64_t));
*pts = global_video_pkt_pts;
pic->opaque = pts;
return ret;
}
void our_release_buffer(struct AVCodecContext *c, AVFrame *pic) {
if (pic)
av_freep(&pic->opaque);
avcodec_default_release_buffer(c, pic);
}

int video_thread(void *arg) {
VideoState *is = (VideoState *) arg;
AVPacket pkt1, *packet = &pkt1;
//int len1;
int frameFinished;
AVFrame *pFrame;
double pts;

pFrame = av_frame_alloc();

for (;;) {
if (packet_queue_get(&is->videoq, packet, 1) < 0) {
// means we quit getting packets
break;
}

pts = 0;

// Save global pts to be stored in pFrame in first call
global_video_pkt_pts = packet->pts;

// Decode video frame
//len1 =
avcodec_decode_video2(is->video_st->codec, pFrame, &frameFinished,
packet);

if (packet->dts == AV_NOPTS_VALUE && pFrame->opaque
&& *(uint64_t*) pFrame->opaque != AV_NOPTS_VALUE) {
pts = *(uint64_t *) pFrame->opaque;
} else if (packet->dts != AV_NOPTS_VALUE) {
pts = packet->dts;
} else {
pts = 0;
}
pts *= av_q2d(is->video_st->time_base);

// Did we get a video frame?
if (frameFinished) {
pts = synchronize_video(is, pFrame, pts);
if (queue_picture(is, pFrame, pts) < 0) {
break;
}
}
av_free_packet(packet);
}
av_free(pFrame);
return 0;
}

int stream_component_open(VideoState *is, int stream_index) {

AVFormatContext *pFormatCtx = is->pFormatCtx;
AVCodecContext *codecCtx;
AVCodec *codec;
SDL_AudioSpec wanted_spec, spec;

if (stream_index < 0 || stream_index >= pFormatCtx->nb_streams) {
return -1;
}

// Get a pointer to the codec context for the video stream
codecCtx = pFormatCtx->streams[stream_index]->codec;

if (codecCtx->codec_type == AVMEDIA_TYPE_AUDIO) {
// Set audio settings from codec info
wanted_spec.freq = codecCtx->sample_rate;
wanted_spec.format = AUDIO_S16SYS;
wanted_spec.channels = codecCtx->channels;
wanted_spec.silence = 0;
wanted_spec.samples = SDL_AUDIO_BUFFER_SIZE;
wanted_spec.callback = audio_callback;
wanted_spec.userdata = is;

if (SDL_OpenAudio(&wanted_spec, &spec) < 0) {
fprintf(stderr, "SDL_OpenAudio: %s\n", SDL_GetError());
return -1;
}
is->audio_hw_buf_size = spec.size;
}
codec = avcodec_find_decoder(codecCtx->codec_id);
if (!codec || (avcodec_open2(codecCtx, codec, NULL) < 0)) {
fprintf(stderr, "Unsupported codec!\n");
return -1;
}

switch (codecCtx->codec_type) {
case AVMEDIA_TYPE_AUDIO:
is->audioStream = stream_index;
is->audio_st = pFormatCtx->streams[stream_index];
is->audio_buf_size = 0;
is->audio_buf_index = 0;

/* averaging filter for audio sync */
is->audio_diff_avg_coef = exp(log(0.01 / AUDIO_DIFF_AVG_NB));
is->audio_diff_avg_count = 0;
/* Correct audio only if larger error than this */
is->audio_diff_threshold = 2.0 * SDL_AUDIO_BUFFER_SIZE
/ codecCtx->sample_rate;

memset(&is->audio_pkt, 0, sizeof(is->audio_pkt));
packet_queue_init(&is->audioq);
SDL_PauseAudio(0);
break;
case AVMEDIA_TYPE_VIDEO:
is->videoStream = stream_index;
is->video_st = pFormatCtx->streams[stream_index];

is->sws_ctx = sws_getContext(is->video_st->codec->width,
is->video_st->codec->height, is->video_st->codec->pix_fmt,
is->video_st->codec->width, is->video_st->codec->height,
AV_PIX_FMT_YUV420P, SWS_FAST_BILINEAR, NULL, NULL, NULL);

is->frame_timer = (double) av_gettime() / 1000000.0;
is->frame_last_delay = 40e-3;
is->video_current_pts_time = av_gettime();

packet_queue_init(&is->videoq);
is->video_tid = SDL_CreateThread(video_thread, is);
codecCtx->get_buffer = our_get_buffer;
codecCtx->release_buffer = our_release_buffer;
break;
default:
break;
}

return 0;
}

int decode_interrupt_cb(void *opaque) {
return (global_video_state && global_video_state->quit);
}

int decode_thread(void *arg) {

VideoState *is = (VideoState *) arg;
AVFormatContext *pFormatCtx = NULL;
AVPacket pkt1, *packet = &pkt1;

int video_index = -1;
int audio_index = -1;
int i;

is->videoStream = -1;
is->audioStream = -1;

AVIOInterruptCB interupt_cb;

global_video_state = is;

// will interrupt blocking functions if we quit!
interupt_cb.callback = decode_interrupt_cb;
interupt_cb.opaque = is;
if (avio_open2(&is->io_ctx, is->filename, 0, &interupt_cb, NULL)) {
fprintf(stderr, "Cannot open I/O for %s\n", is->filename);
return -1;
}

// Open video file
if (avformat_open_input(&pFormatCtx, is->filename, NULL, NULL) != 0)
return -1; // Couldn't open file

is->pFormatCtx = pFormatCtx;

// Retrieve stream information
if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
return -1; // Couldn't find stream information

// Dump information about file onto standard error
av_dump_format(pFormatCtx, 0, is->filename, 0);

// Find the first video stream

for (i = 0; i < pFormatCtx->nb_streams; i++) {
if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO
&& video_index < 0) {
video_index = i;
}
if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO
&& audio_index < 0) {
audio_index = i;
}
}
if (audio_index >= 0) {
stream_component_open(is, audio_index);
}
if (video_index >= 0) {
stream_component_open(is, video_index);
}

if (is->videoStream < 0 || is->audioStream < 0) {
fprintf(stderr, "%s: could not open codecs\n", is->filename);
goto fail;
}

// main decode loop

for (;;) {
if (is->quit) {
break;
}

// seek stuff goes here
if (is->seek_req) {
int stream_index = -1;
int64_t seek_target = is->seek_pos;

if (is->videoStream >= 0)
stream_index = is->videoStream;
else if (is->audioStream >= 0)
stream_index = is->audioStream;

if (stream_index >= 0) {
seek_target = av_rescale_q(seek_target, AV_TIME_BASE_Q,
pFormatCtx->streams[stream_index]->time_base);
}
if (av_seek_frame(is->pFormatCtx, stream_index, seek_target,
is->seek_flags) < 0) {
fprintf(stderr, "%s: error while seeking\n",
is->pFormatCtx->filename);
} else {
if (is->audioStream >= 0) {
packet_queue_flush(&is->audioq);
packet_queue_put(&is->audioq, &flush_pkt);
}
if (is->videoStream >= 0) {
packet_queue_flush(&is->videoq);
packet_queue_put(&is->videoq, &flush_pkt);
}
}
is->seek_req = 0;
}

if (is->audioq.size > MAX_AUDIOQ_SIZE
|| is->videoq.size > MAX_VIDEOQ_SIZE) {
SDL_Delay(10);
continue;
}

if (av_read_frame(is->pFormatCtx, packet) < 0) {
if (is->pFormatCtx->pb->error == 0) {
SDL_Delay(100); /* no error; wait for user input */
continue;
} else {
break;
}
}

// Is this a packet from the video stream?
if (packet->stream_index == is->videoStream) {
packet_queue_put(&is->videoq, packet);
} else if (packet->stream_index == is->audioStream) {
packet_queue_put(&is->audioq, packet);
} else {
av_free_packet(packet);
}
}

/* all done - wait for it */
while (!is->quit) {
SDL_Delay(100);
}

fail: {
SDL_Event event;
event.type = FF_QUIT_EVENT;
event.user.data1 = is;
SDL_PushEvent(&event);
}
return 0;
}

void stream_seek(VideoState *is, int64_t pos, int rel) {

if (!is->seek_req) {
is->seek_pos = pos;
is->seek_flags = rel < 0 ? AVSEEK_FLAG_BACKWARD : 0;
is->seek_req = 1;
}
}

int main(int argc, char *argv[]) {

SDL_Event event;
//double pts;
VideoState *is;

is = av_mallocz(sizeof(VideoState));
char filePath[] = "./src/a.mp4";

// Register all formats and codecs
av_register_all();

if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {
fprintf(stderr, "Could not initialize SDL - %s\n", SDL_GetError());
exit(1);
}

// Make a screen to put our video
#ifndef __DARWIN__
screen = SDL_SetVideoMode(640, 480, 0, 0);
#else
screen = SDL_SetVideoMode(640, 480, 24, 0);
#endif
if (!screen) {
fprintf(stderr, "SDL: could not set video mode - exiting\n");
exit(1);
}

av_strlcpy(is->filename, filePath, sizeof(is->filename));

is->pictq_mutex = SDL_CreateMutex();
is->pictq_cond = SDL_CreateCond();

schedule_refresh(is, 40);

is->av_sync_type = DEFAULT_AV_SYNC_TYPE;

is->parse_tid = SDL_CreateThread(decode_thread, is);
if (!is->parse_tid) {
av_free(is);
return -1;
}
av_init_packet(&flush_pkt);
flush_pkt.data = (unsigned char *) "FLUSH";
for (;;) {
double incr, pos;
SDL_WaitEvent(&event);
switch (event.type) {
case SDL_KEYDOWN:
switch (event.key.keysym.sym) {
case SDLK_LEFT:
incr = -10.0;
goto do_seek;
case SDLK_RIGHT:
incr = 10.0;
goto do_seek;
case SDLK_UP:
incr = 60.0;
goto do_seek;
case SDLK_DOWN:
incr = -60.0;
goto do_seek;
do_seek: if (global_video_state) {
pos = get_master_clock(global_video_state);
pos += incr;
stream_seek(global_video_state,
(int64_t) (pos * AV_TIME_BASE), incr);
}
break;
default:
break;
}
break;
case FF_QUIT_EVENT:
case SDL_QUIT:
SDL_CondSignal(is->audioq.cond);
SDL_CondSignal(is->videoq.cond);
is->quit = 1;
SDL_Quit();
exit(0);
break;
case FF_ALLOC_EVENT:
alloc_picture(event.user.data1);
break;
case FF_REFRESH_EVENT:
video_refresh_timer(event.user.data1);
break;
default:
break;
}
}
return 0;

}