On Fri, Dec 17, 2010 at 9:55 AM, Tomas Härdin <[email protected]>wrote:

> On Thu, 2010-12-16 at 14:57 -0800, Pushkar Pradhan wrote:
> > On Thu, Dec 16, 2010 at 2:44 PM, Eli Konky <[email protected]> wrote:
> >
> > > Thanks.
> > >
> > > I know the delay because the module that produced the video can report
> the
> > > delay.
> > > In some cases I'll use a human (maybe with vlc player that has a
> > > compensation feature)
> > >
> > > Can I please ask you for a direction on how to rewrite pts? can I use
> > > ffmpeg
> > > to do that?
> > >
> > > Thanks
> > > Eli
> > >
> > > On Fri, Dec 17, 2010 at 12:38 AM, Pushkar Pradhan <
> > > [email protected]
> > > > wrote:
> > >
> > > > On Thu, Dec 16, 2010 at 9:44 AM, Eli Konky <[email protected]>
> wrote:
> > > >
> > > > > Hi,
> > > > >
> > > > > I have an mp4 (h.264, aac) file where the audio is lagging behind
> the
> > > > > video.
> > > > >
> > > > > Is it possible to fix this file by just rewriting pts somehow,
> without
> > > > > decoding and re-encoding the entire file?
> > > > > Is there any other way to deal with this?
> > > > >
> > > > > Thanks
> > > > > Eli
> > > > > _______________________________________________
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> > > > > [email protected]
> > > > > https://lists.mplayerhq.hu/mailman/listinfo/libav-user
> > > > >
> > > >
> > > > You can rewrite the pts without doing any decoding/encoding. But how
> do
> > > you
> > > > know what is the correct adjustment? You can do trial and error, e.g.
> add
> > > > +50 msec, 100 msec and check the result visually. But what if the lag
> is
> > > > varying over time?
> > > >
> > > > --
> > > > pushkar
> > > > _______________________________________________
> > > > libav-user mailing list
> > > > [email protected]
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> > > >
> > > _______________________________________________
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> > >
> >
> > As you read the frames (in AVPacket I believe) you can write it out by
> > modifying the AVPacket.pts value. I don't have much experience coding
> with
> > libavcodec so please look at the examples. You can probably use ffmpeg
> too,
> > you will have to scan through the many CLI options it provides.
> > By the way, please do not top post mailing list users do not like it :-)
>
> I don't think ffmpeg has an option for adjusting the timestamps of the
> streams. It shouldn't be too hard to hack one in though.
>
> Look at how the options are specified, then look at the logic for
> -vcodec copy (or -acodec copy). Whenever you get a packet you add
> av_rescale_q(us_adjust, AV_TIME_BASE_Q, ist->time_base) to both
> timestamps (unless they're AV_NOPTS_VALUE). us_value is your adjustment
> in microseconds (aka AV_TIME_BASE).
>
> /Tomas
>
>
> _______________________________________________
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>
>
Thanks.
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