[FFmpeg-devel] Timestamp issues in live RTP->mpegts bridges

Luca Abeni lucabe72
Tue Jan 20 16:22:37 CET 2009

Hi Alexandre,

> Luca Abeni wrote:
>> This looks like something for the codecs guys: can you open an issue on
>> the bugtracker, or send an email in a new thread describing this problem?
>> (you will have to upload the H.263 bitstream on upload.ffmpeg.org, as
>> indicated in the bugreport page).
> What I don't understand is that independently from the codec, looking at 
> the RTP timestamps, they are  incremented by 6036 or 5946 per frame, 
> which is roughly 15fps for a clock of 90kHz. But maybe this information 
> is not exploited ?

As Michael pointed out, the 29.97 thing is the time base of the codec, which
for H.263 is not related with the stream frame rate.

RTP timestamps are associated to AVPackets, while codec's timestamps are
associated to AVFrames, I think. Try to print them and to compare the values,
to see if this can shed some light on the situation.

>>> Also, I was wondering: instead of giving a fixed frame rate, is there a 
>>> way of just inheriting the input timestamps ?
>> I think what you want here is variable frame-rate... I do not know if
>> H.263 supports it. If yes, in theory you should not need any additional
>> command line option (but I am not sure, as I have no experience with
>> variable frame-rate).
>> Anyway, I think you are now hitting a codec-related bug...

According to latest email from Michael, I have to correct myself, as it
seems that this is not a bug... The problem must be somewhere else (maybe
ffmpeg is not properly using the RTP timestamps, I do not know...)


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