【音视频】ffplay解析-音视频同步

一个国际标准：音频帧-视频帧时间戳的差值在-100ms~25ms内流畅
1.差值=音频播放时间戳-视频播放时间戳----diff=pts_audio-pts_video（注意区分！！）
2.判断逻辑:
	(无法感知区间：min=-125ms,max=45ms)
	- max

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ffplay具体源码

 /* if video is slave, we try to correct big delays by
    duplicating or deleting a frame
    通过重复帧或者删除帧来纠正延迟*/
 diff = get_clock(&is->vidclk) - get_master_clock(is);

 /* skip or repeat frame. We take into account the
    delay to compute the threshold. I still don't know
    if it is the best guess */
 sync_threshold = FFMAX(AV_SYNC_THRESHOLD_MIN,
                        FFMIN(AV_SYNC_THRESHOLD_MAX, delay));
 if (!isnan(diff) && fabs(diff) < is->max_frame_duration) { // diff在最大帧duration内
     if (diff <= -sync_threshold) {      // 视频已经落后了
         delay = FFMAX(0, delay + diff); // 上一帧持续的时间往小的方向去调整
     }
     else if (diff >= sync_threshold && delay > AV_SYNC_FRAMEDUP_THRESHOLD) {
         // 视频超前
         delay = delay + diff; // 上一帧持续时间往大的方向去调整
         av_log(NULL, AV_LOG_INFO, "video: delay=%0.3f A-V=%f\n",
                delay, -diff);
     }
     else if (diff >= sync_threshold) {
         // 上一帧持续时间往大的方向去调整
         delay = 2 * delay; // 保持在 2 * AV_SYNC_FRAMEDUP_THRESHOLD内, 即是2*0.1 = 0.2秒内
     } else {
         // 音视频同步精度在 -sync_threshold ~ +sync_threshold
         // 其他条件就是 delay = delay; 维持原来的delay, 依靠frame_timer+duration和当前时间进行对比
     }
 }
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