[Ffmpeg-devel] Bug in pts computation in compute_pkt_fields() ?

[Martin Wache]

Wolfram Gloger schrieb:
> Hi,
> 
>> I'm experiencing problems with the pts values of the audio packets given
>> by av_read_frame(). The stream I feed to ffmpeg is a DVB-T stream mpeg2
>> audio and video.
> 
> That is probably raw mpeg-ts, right?
> 
No, it is already remuxed to pes.

>> I'm not sure if it is just me getting the interface right, so I did some
>> debugging, and here is what I found:
>> First, I get audio frames without pts, the result is that st->cur_dts is
>> set to 0 and starts to grow according to the length of the audio, which
>> is fine. But as soon as I get a packet with pts, everything gets messed
>> up by the lines
>>
>>    /* handle wrapping */
>>     if(st->cur_dts != AV_NOPTS_VALUE){
>>         if(pkt->pts != AV_NOPTS_VALUE)
>>             pkt->pts= lsb2full(pkt->pts, st->cur_dts, st->pts_wrap_bits);
>>         if(pkt->dts != AV_NOPTS_VALUE)
>>             pkt->dts= lsb2full(pkt->dts, st->cur_dts, st->pts_wrap_bits);
>>     }
>>
>> The result is negative pts value for the packet. So I guess this is a
>> bug in compute_pkt_fields(), or am I doing something wrong?
> 
> Please check that st->pts_wrap_bits is set to 60 (and not 33) if the
> input stream is mpeg-ts.  A long time ago I had a similar problem
> which was caused by the transport stream not being detected correctly.
>

Hmm, you are right, st->pts_wrap_bits is 33 and it should be 60. If I
manually set it to 60 it works as it should. How did you fix that problem?

Thank you very much!

Martin