In a video previewer that I am writing, I am trying to synchronize the audio to
the video as in ffplay.c with av_sync_type = AV_SYNC_VIDEO_MASTER. The
resulting audio seems to be in sync with the video; however, it is warbly, like
it's playing through water or something. Obviously, I am missing something in
mimicking the technique from ffplay.c
In synchronize_audio() of ffplay.c, there is this line:
diff = get_audio_clock(is) - get_master_clock(is);
I am using the get_audio_clock() as in ffplay, but for the get_master_clock(),
I am using a custom get_video_clock() directly, as I will always be syncing to
the video. However, I am not using the same function as in ffplay.c, because I
am not handling the video stream through a PacketQueue.
My app performs video analysis on the video frames as they are decoded and then
passes them to a Windows C# UI for display and optional saving to disk. The
throughput of the video analysis drives the video playback. That is, when it
is done processing a frame, then it requests the next one. If the processing
takes less time than a frame interval, then I insert a delay to ensure that the
playback is close to real time for the user. (Maybe this is not the best
design?)
Therefore, I would like the audio to follow the video. The problem seems to be
in getting the proper value for the video "clock". To this end, I have been
using a function as in Dranger's tutorial06.c:
double get_video_clock(VideoState *is) {
double delta;
delta = (av_gettime() - video_current_pts_time) / 1000000.0;
return video_current_pts + delta;
}
where delta is amount of time since the video_current_pts was obtained. Seems
to me that this should work in my context, yet the result is not yet
acceptable. If I change the function to simply
return video_current_pts;
Then the warble is more pronounced.
How do I get the audio to properly synchronize with the video?
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