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 
     
      #include 
      
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              #ifdef __MINGW32__#undef main /* Prevents SDL from overriding main() */#endif#include 
              
               #include 
               
                #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 audiotypedef 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; ///
                
                 
                  
                   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;}