[Libav-user] How to calculate pts/dts ???

[Paul B Mahol]

On Thu, Jan 5, 2023 at 3:43 PM wolverin via Libav-user <
libav-user at ffmpeg.org> wrote:

> On Mon, Jan 2, 2023 at 4:51 PM wolverin via Libav-user <
> libav-user at ffmpeg.org
> <//e.mail.ru/compose/?mailto=mailto%3alibav%2duser at ffmpeg.org>> wrote:
>
> Did I understand you correctly that I need to multiply time_base and
> system time between adjacent frames and add the resulting time to the
> previous PTS?
>
> Nope.
> PTS is just timebase * seconds represented as int64 number
>
> There are no additions with next/prev pts values.
>
>
>
> Then pts is the time of one frame?
>
>
> Yes, when used with tied time_base AVRational.
>
>
> Thank you very much, you helped me a lot, it significantly improved the
> smoothness of playback, but I still see 1 or 2 incomprehensible pauses at
> the beginning when watching live video in VLC.
>
> Currently, only the output AVStream->time_base is used to calculate
> pts/dts.
> But then what is the outgoing AVCodecContext->time_base needed for and
> what values? Do I need to initialize AVStream->avg_frame_rate or
> AVStream->r_frame_rate? Their change does not affect almost the video, but
> for some reason it increases traffic.
>
>
> avcodec_send_packet(pCdcCtxInp, pPktInp);
> avcodec_receive_frame(pCdcCtxInp, pFrm);
> pFrm->pts = av_rescale_q(pPktInp->pts, pFmtCtxInp->streams[0]->time_base,
> pCdcCtxInp->time_base);
>
> avcodec_send_frame(pCdcCtxOut, pFrm);
> avcodec_receive_packet(pCdcCtxOut, pPktOut);
> pPktOut->pts = av_rescale_q(pFrm->pts, pCdcCtxInp->time_base,
> pCdcCtxOut->time_base);
> pPktOut->dts = pPktOut->pts;
>
>
> Inspect values of input/output pts and used timebases(with printfs or
> other ways...) and you can figure it where PTS becomes nonsense.
>
>
> As I understand it, the input stream from the usb camera has a constant
> FR, transcoded I get a variable FR +
> I can start reading earlier frames from the camera additionally for
> writing to disk, so I can't scale timestamps directly.
>

If you use libx264 encoder, have you tried tune zerolatency compensation
flag?


>
>
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