[FFmpeg-devel] [PATCH 3/3] avdevice: use av_gettime_relative() for timestamps

[Kieran Kunhya]

On Sun, 7 Feb 2021, 17:15 Nicolas George, <george at nsup.org> wrote:

> Kieran Kunhya (12021-02-07):
> > Yes the montonic clock should be the default.
>
> Changing the default is acceptable to me. Probably after a transition
> period.
>
> > You misunderstand greatly. How does the clock rate of NTP magically make
> > its way to the camera?
>
> I do not know, I do not care, I am not a driver developer. All I know is
> that the kernel can give me a timestamp based on the NTP-synchronized
> wall time clock, and that it has better than 1/100 second accuracy,
> which is plenty enough for must use cases.
>

You do care because different sources generated either by a PC or different
physical cameras will drift. E.g at 25fps after one hour you might get
90000 frames from one and 90002 or whatever frames from another etc. And of
course the timestamps will drift slowly. Unfortunately you seem to share
the same fundamental misunderstandings as the kernel developers.

Applications like VLC and upipe have sophisticated filtering and drift
compensation to correct all of this.

Kieran

Regards,
>
> --
>   Nicolas George
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