出处见链接

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https://blog.csdn.net/myvest/article/details/97416415

{
    video->frameq.deQueue(&video->frame);

    double current_pts = *(double *)video->frame->opaque;//当前帧的pts
    double delay = current_pts - video->frame_last_pts;//相减之后 就是前帧默认的时间
    if (delay <= 0 || delay >= 1.0)
    {
        delay = video->frame_last_delay;//数据波动太大 特殊处理
    }
   
    double ref_clock = audio->get_audio_clock();//参考时间
    double diff = current_pts - ref_clock;//应该播放时间-当前时间 = 偏差时间 diff < 0 :video slow,diff > 0 :video fast
    
    double sync_threshold = FFMAX(MIN_SYNC_THRESHOLD, FFMIN(MAX_SYNC_THRESHOLD, delay)) ;//规定帧播放时间在一定范围内
    
    audio->audio_wait_video(current_pts,false);//更新时钟
    video->video_drop_frame(ref_clock,false);

    if (!isnan(diff) && fabs(diff) < NOSYNC_THRESHOLD) // 不同步
    {
        if (diff <= -sync_threshold)//视频比音频慢，加快
        {
            delay = FFMAX(0,  delay + diff);//表示直接覆盖上一帧
            static int last_delay_zero_counts = 0;
            if(video->frame_last_delay <= 0)
            {
                last_delay_zero_counts++;
            }
            else
            {
                last_delay_zero_counts = 0;
            }
            if(diff < -1.0 && last_delay_zero_counts >= 10)//连续缓慢 视频解码跟不上
            {
                printf("maybe video codec too slow, adjust video&audio\n");
                #ifndef DORP_PACK
                audio->audio_wait_video(current_pts,true);//差距较大，需要反馈音频等待视频
                #endif          
                video->video_drop_frame(ref_clock,true);//差距较大，需要视频丢帧追上
            }
        }//视频比音频快，减慢
        else if (diff >= sync_threshold && delay > SYNC_FRAMEDUP_THRESHOLD)//快了一帧以上  该帧与前帧相差了不少
            delay = delay + diff;//直接跳过去
        else if (diff >= sync_threshold)
            delay = 2 * delay;//音视频差距较小，加倍延迟，逐渐缩小
    }
    video->frame_last_delay = delay;//该帧从current_pts播放了delay时长
    video->frame_last_pts = current_pts;

    double curr_time = static_cast<double>(av_gettime()) / 1000000.0;
    if(video->frame_timer == 0)
    {
        video->frame_timer = curr_time;//第一次
    }

    double actual_delay = video->frame_timer + delay - curr_time;//应该为curr_time-video->frame_timer + delay
    if (actual_delay <= MIN_REFRSH_S)
    {
        actual_delay = MIN_REFRSH_S;
    }
    usleep(static_cast<int>(actual_delay * 1000 * 1000));
    //printf("actual_delay[%lf] delay[%lf] diff[%lf]\n",actual_delay,delay,diff);
    // Display
    SDL_UpdateTexture(video->texture, &(video->rect), video->frame->data[0], video->frame->linesize[0]);
    SDL_RenderClear(video->renderer);
    SDL_RenderCopy(video->renderer, video->texture, &video->rect, &video->rect);
    SDL_RenderPresent(video->renderer);
    video->frame_timer = static_cast<double>(av_gettime()) / 1000000.0 ;//刷新一帧显示时间
    
    av_frame_unref(video->frame);
    
    //update next frame
    schedule_refresh(media, 1);
}