[Libav-user] AVFrame pts and av_usleep funciton.

[Richard Hussong]

On Mon, Aug 21, 2023 at 5:48 AM Denis Gottardello <info at denisgottardello.it>
wrote:

>
> Thanks for you reply.
>
> So these lines of code:
>
> int64_t pts= av_rescale(pAVFrame->pts,
> pAVCodecContextVideo->framerate.den, pAVCodecContextVideo->framerate.num);
>
> printf("pts, %d\n", pts);
>
> Should print the timestamp (as time_t) of each frame? Is the pts value
> calculated correctly?
>

To use usleep, you need to convert the PTS interval to a number of
microseconds using something like

int64_t usecs = av_rescale_q( pts - prev_pts, video_timebase, us_timebase )

where "video_timebase" is the timebase of the video PTS values and
"us_timebase" is the microsecond timebase: num = 1, den = 1000000.

- Richard Hussong

>
> In data lunedì 21 agosto 2023 11:15:06 CEST, Paul B Mahol ha scritto:
>
> > On Mon, Aug 21, 2023 at 10:30 AM Denis Gottardello
>
> > <info at denisgottardello.it>
>
> > wrote:
>
> > > In order to implement a sleep function and wait the right time to
> display
>
> > > a frame I have written this code:
>
> > >
>
> > > int framerate= pAVCodecContextVideo->framerate.num /
>
> > > pAVCodecContextVideo->framerate.den;
>
> > >
>
> > > if (previous!= 0) {
>
> > >
>
> > >     av_usleep((pAVFrame->pts - previous) / framerate);
>
> > >
>
> > > }
>
> > >
>
> > > previous= pAVFrame->pts;
>
> > >
>
> > > but the value passed to av_usleep() is wrong.
>
> > >
>
> > > How have I to calculate it?
>
> >
>
> > If you really want to do it that way you need to use floating point
>
> > calculations, or use fixed point arithmetic (av_rescale*)
>
> > to convert seconds to microseconds.
>
> >
>
> > > Best regards.
>
> > >
>
> > >
>
> > > --
>
> > >
>
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>
> > >
>
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>
> > >
>
> > > http://www.denisgottardello.it
>
> > >
>
> > > GMT+1
>
> > >
>
> > > Skype: mrdebug
>
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>
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>
> http://www.denisgottardello.it
>
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>
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