[Libav-user] Getting frame duration when decoding

[Leonid Mokruschin]

Hi Vahid:

 

perhaps you need to take into account pStream->codec.time_base and
pStream->codec.ticks_per_frame. I believe that pStream->time_base matches to
frame rate for interleaved video streams, whereas pStream->codec.time_base
matches to field rate. E.g. for 25fps interleaved stream you will get
time_base=1/25 but codec.time_base=1/50 and codec.ticks_per_frame==2.

 

Sincerely,

LM

 

 

 

 

From: libav-user-bounces at ffmpeg.org [mailto:libav-user-bounces at ffmpeg.org]
On Behalf Of Vahid Kowsari
Sent: Monday, July 08, 2013 3:02 AM
To: libav-user at ffmpeg.org
Subject: [Libav-user] Getting frame duration when decoding

 

Hi All,

 

I am decoding some MPEG-2 and H264 streams from file and have a problem
getting the correct duration of a frame. Some files are MPEG2 transport
streams while other are wrapped in mp4 or MOV container.

 

I use the following section of code 

    pFrame is the input AVFrame after decoding

 

    AVStream *pStream = pCtx->pFormatCtx->streams[pCtx->activeVideoStream];

    double time_base = av_q2d(pStream->time_base);

    double duration = time_base * av_frame_get_pkt_duration(pFrame);

    duration +=  duration * (pFrame->repeat_pict / 2);

 

My problem is that for alot of streams this works while for others streams
the duration needs to be multipled by 2 for the timing to work
correctly...even though repeat_pic is 0. I checked interlace flag but in the
files that I had the problem, they are both interlaced.

 

What timebase is the correct timebase to use? The codec timebase or the
stream timebase?

 

How do I correctly get the duration of a frame regardless of the type of
file and the encoding parameters that were used?

 

Thanks much for your help!

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://ffmpeg.org/pipermail/libav-user/attachments/20130708/0d0a9994/attachment.html>