[Libav-user] Fw: strange H264 audio sync behavior

Marco Sieber l-spy at web.de
Mon Jul 21 11:17:02 CEST 2014

Thank you very much for your patient.

> This is unclear to me: "changed it for output 1/25 for codec and stream get changed to 1/90000"
> Are you setting it now to 1/25 or to 1/90000 ?

Sorry, if i was unclear. I take over the Framerate from InputVideoStream->r_frame_rate and set it to OutputVideoCodec->time_base and OutputVideoStream->r_frame_rate.
Then avformat_new_stream, set the OutputVideoStream->time_base to 1/90000, i guess as default for mp4. But after avformat_write_header, the OutputVideoStream->time_base changes to 1/12800.
And OutputAudioStream->time_base and AudioCodec is 1/48000.

>Why don't you set all to 1/1000, the same value, then it's easy to see if audio and video DTS runs apart after a while.

I can try this and play a little bit but i guess its only for pts/dts, and you cant actually watch the video.

>When you check with ffprobe, do audio and video still have about the same (resulting) DTS/PTS after 5 minutes, or at the end of the movie?

No, but kinda the same duration (only 1 audioframe different), the both Streams has the same length.

>And if that's ok then make sure there are no different values set for timebase or codec parameters in the single streams and in the container. I think that is what >your problem is, why ffplay/VLC stays sync and QT not.

Okay ... hmmm.. but video and audio stream, doesnt they need different timebases? Because, you want video stream with 90khz and audio 48khz?

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