[pulseaudio-discuss] [PATCH] bluetooth: Correct fixed latency for HSP sink

Tanu Kaskinen tanuk at iki.fi
Tue Feb 14 10:40:59 UTC 2017

On Tue, 2017-02-14 at 10:51 +0100, Georg Chini wrote:
> On 14.02.2017 10:25, Tanu Kaskinen wrote:
> > On Sat, 2017-02-04 at 19:34 +0100, Georg Chini wrote:
> > > The fixed latency for the HSP sink was set to 125 ms plus one write block size.
> > > pa_sink_get_latency() however returns 28 ms like it does for A2DP and also for
> > > the HSP source.
> > > Therefore this patch corrects the fixed latency of the HSP sink to 25 ms plus
> > > one write block size, assuming that the original value of 125 ms was a typo.
> > 
> > I believe latency reporting in module-bluez5-device is broken, so it
> > can't be used as a justification for changing the constants. module-
> > bluez4-device includes the fixed latency in its latency reports.
> > module-bluez5-device does that too, but it only uses the A2DP constants
> > (even when HSP is active). That's probably because originally module-
> > bluez5-device only supported A2DP, and when HSP support was added
> > later, updating the latency reporting code was just forgotten.
> > 
> Thanks for the review. You are right, the correct justification would be,
> that it can be expected that HSP recording produces the same delay as
> playback.
> Do you think it is OK if I send a fix for the other bug (which looks easy
> to fix) and include that change? Or would you prefer to leave the constants
> as they are?

I'd prefer leaving the constants as they are if there's no hard
evidence of them being wrong. I think this should be quite easy to
test: just play a video using HSP with old and new constant values, and
if the new value results in better A/V sync, that's good enough
evidence for me.



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