[Libav-user] Add frame rate after muxing

[SAkonst]

Hello!

Please, Help. 

I try to write video from camera to mkv container with libavformat. 
Use lagarith codec (FourCC "lags") 

In my case I receive an image from camera, but a frame rate is not known before recording. I can calculate it just after I stop recording. 

How can I add frame rate into header after muxing? Is it possible at all?
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Best regards,
 SAkonst                          mailto:SAkonst at gmail.com