[libav-api] Encoding video with non-fixed FPS

Luca Barbato lu_zero at gentoo.org
Thu Dec 29 17:43:41 CET 2011


On 29/12/11 17:22, Soren Dreijer wrote:
> Thanks for the quick replies, Luca!
>
>>> So, rather than setting the timebase to 1/<fps>   as e.g.
>>> output-example.c does, I'd simply set it to 1/1000 if my incoming
>>> timestamps are in milliseconds? Let's say I capture my first frame a 0
>>> ms and the second frame a 45 ms. Should I then set the frames' pts to
>>> 0 and 45, respectively in the AVPacket?
>>
>> should work.
>
> Where do I set pts timebase? If I change the AVCodecContext::time_base
> from 1/25 to 1/1000, the resulting FPS of the video is 1000, which
> isn't what I want. I still want 25 FPS, but I'd like to have more
> granularity when specifying each frame's pts.

fps information on a non-constant frame rate stream is a bit misleading...

Yet, you have a time_base in the stream description.

>> The encoder does not care about pts, the muxer will and depending on it you
>> might have to use such tricks.
>
> That's where I get confused because I just call
> av_interleaved_write_frame() with the AVPacket with the correct pts
> and the muxer is "hidden" from me (as far as I know?). It sounds like
> I shouldn't rely on the muxer to be clever enough to handle dropped
> frames then?

All depends on the container format =)

lu

-- 

Luca Barbato
Gentoo/linux
http://dev.gentoo.org/~lu_zero



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