[Libav-user] Muxing mpeg4-ts and raw audio to AVI file

[Nicholas Butts]

Dmitry Gorbunov wrote:

> Why dts? Because it's more reliable than pts after decoding (I presume you
> avcodec_decode_video on input packet to get raw video frame suitable for
> encoding).

I am not currently using avcodec_decode_video, I don't want to recompress
the image data. I just want to take the MPEG4-TS stream and mux it with raw
audio data. This is the basic flow of the encoding chain:

image sensor -> hardware capture -> hardware codec -> muxed with audio to an
AVI file

I've been assigned the MPEG-4 data directly to AVPacket data pointer and
then calling av_interleaved_write_frame. I can use ffmpeg to extract the
audio and video, so it kinda of works, it just doesn't play back nicely in
mplayer or vlc. I will look more into the dts member.

Thanks.


On Sun, Aug 14, 2011 at 10:53 PM, Dmitry Gorbunov <atskiisotona at gmail.com>wrote:

>
> Nicholas Butts wrote:
> >
> >     if (c->coded_frame && c->coded_frame->pts != AV_NOPTS_VALUE)
> >         pkt.pts= av_rescale_q(c->coded_frame->pts, c->time_base,
> > _videoStream->time_base);
> >
>
> c->coded_frame->pts is a synthetic value produced by video encoder (usually
> 0, 1, 2, 3, etc). It may be good for constant frame rates, but sometimes
> fails even then. And I believe that your case is related to variable frame
> rate. I don't know for sure, but most hardware devices seem to produce
> variable frame rate streams. My two web cameras do that at least.
>
> You should use input_packet.dts (packet you read from input mpeg stream via
> av_read_frame) and rescale it by input_stream->time_base and
> output_stream->time_base:
>
> pkt.pts = av_rescale_q(input_packet.pts, input_stream->time_base,
> output_stream->time_base); // of course condition is not required
>
> Why dts? Because it's more reliable than pts after decoding (I presume you
> avcodec_decode_video on input packet to get raw video frame suitable for
> encoding).
>
> The above solution works for me on my web cameras, I hope it helps you.
>
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-- 
Nicholas Butts
SENIOR FIRMWARE ENGINEER

Appareo Systems, LLC
1810 NDSU Research Circle N
Fargo, ND 58102

P: (701) 356-2200
F: (701) 356-3157

http://www.appareo.com

nbutts at appareo.com



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