[vlc-devel] [PATCH v3 2/6] clock: add vlc_clock_main_SetInputDrift

Alexandre Janniaux ajanni at videolabs.io
Tue Mar 16 21:41:51 UTC 2021


On Tue, Mar 16, 2021 at 11:18:58PM +0200, Rémi Denis-Courmont wrote:
> Le tiistaina 16. maaliskuuta 2021, 22.45.36 EET Alexandre Janniaux a écrit :
> > > - Sometimes playback never "catches up".
> >
> > What do you mean by «never catches up»?
> The same symptoms as Thomas claims to be happening now.
> > > - Especially as start/resume, doppler sound effect (resampling) due to
> > > abnormally quick succession of SetPCR calls.
> > The «doppler sound effect» on 3.0 and the artifacts were
> > happening because of the way this clock was implemented, ie
> > it's only about how you resample and filter the result.
> No. It's about how the clock was measured. Resampling was working as intended
> when the master clock and the audio clock drift from one another.

If you squeeze audio, it will get pitched up, so you need to
be sure there's silence in that place, or audio that has been
stretched to match the frequency used. Using the input PCR as
clock will guarantee that there are audio glitch someday, but
it's cannot generate high pitch sound. Clock is about time, not

> > It doesn't mean that using the input PCR is incorrect.
> Actually, it does mean exactly that.

My interpretation is arbitrary too but is at least sustained
by the clock design document. Can you be more explicit about
why it means exactly that for you?

Alexandre Janniaux

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