[vlc-devel] [PATCH 1/2] aout: send the preferred period delay to modules

Rémi Denis-Courmont remi at remlab.net
Mon Feb 11 17:26:30 CET 2019

Le maanantaina 11. helmikuuta 2019, 17.59.53 EET Thomas Guillem a écrit :
> On Mon, Feb 11, 2019, at 16:57, Rémi Denis-Courmont wrote:
> > 	Hi,
> > 
> > The period is a feature of (most) hardware, and I'm not clear why the core
> > should know about it or even what would be the definition of "period
> > hint". I am also not clear what "period delay" means.
> What about the jitter (or buffering) value  of the output clock ? It should
> be calculted from the period, no ? (2 times the period we agreed).

The jitter of the audio clock is probably negligible, and/or hard to measure 
for our purposes.

What really matters is that the audio buffer is filled at least one period plus 
the intrinsic output latency ahead of the play time. Otherwise, the audio 
buffer may underrun.

The rule of thumb is that period should be no more than half the buffer; some 
say a third. But that's only a rule of thumb: it boils down to assuming that 
the intrinsic latency is no more than one period. In fact, this seems like a 
dubious assumption for outputs with extreme long latency such as AirPlay.

Rémi Denis-Courmont

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