[pulseaudio-discuss] [WIP] Passthrough support

[Luiz Augusto von Dentz]

Hi,

On Tue, Mar 15, 2011 at 11:43 AM, Arun Raghavan
<arun.raghavan at collabora.co.uk> wrote:
> On Tue, 2011-03-15 at 01:36 +0530, Arun Raghavan wrote:
>> On Mon, 2011-03-14 at 14:57 -0500, pl bossart wrote:
>> > >> Other things I noticed: the volume is much higher in passthrough mode,
>> > >> maybe we need to find a way to set the volume on the headset to match
>> > >> the volume used for PCM. Also I heard some high-frequency modulations,
>> > >> typically coding noise, maybe there's still something fishy during the
>> > >> mp3 decode part.
>> > >
>> > > I get this sort of thing on, as far as I can tell, one channel as well.
>> > > I figured the decoder on the CSR chip wasn't that great.
>> >
>> > Looks to me that the quality is slightly worse than with the initial
>> > patches, but it's of course a very subjective assessment since I need
>> > to reinstall pulse/gstreamer to check the differences instead of doing
>> > an A/B test. Can you check and make sure the payloader doesn't
>> > skip/change any bytes? If you dump what is actually sent to the
>> > headset and compare to the initial file, you shouldn't have any
>> > deltas.
>>
>> Yep, I did that before I pushed out the code (verified a few frames by
>> hand, but I'll do something more extensive in the morning). I'm still
>> seeing the setconf error, but now that it's at least clear it's
>> connecting to the wrong seid, I'm hoping to get this fixed.
>
> Turns out this was very likely a bluez problem. I've sent in a patch [1]
> that at least gets things working for me. I also see the high-pitched
> pops and clicks (these very definitely weren't there with your
> payloader) - should get that pinned down before long.
>
> I pushed your change along with a fix for the assert you saw to my tree
> as well.

I would suggest to use the new API to implement audio passthrough for
bluetooth devices, it is very likely the we will be disabling unix
socket IPC in BlueZ. What I would do is, if audio passthrough is
supported then PA register a mp3 endpoint and try to configure both
sbc and mp3 simultaneously (only one active at time) when possible so
we can quickly switch between codecs.

> Cheers,
> Arun
>
> [1] http://thread.gmane.org/gmane.linux.bluez.kernel/11715
>
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-- 
Luiz Augusto von Dentz
Computer Engineer