[pulseaudio-discuss] [PATCH v5 0/7] New API for Bluetooth A2DP codecs

[Tanu Kaskinen]

On Sat, 2019-01-19 at 18:11 +0100, Pali Rohár wrote:
> This is 5th version of my patch series for modular A2DP codec API and
> aptX support. The only change for v5 is support for switching codecs.
> 
> This patch series provides new modular API for Bluetooth A2DP codecs,
> clean up module-bluez5-device and bluez5-util to be codec independent
> and convert SBC codec into this new API for A2DP codecs. Also it adds
> support for aptX, aptX HD and FastStream A2DP codecs.
> 
> New codec API is designed in way, that for adding new codec is not
> needed to touch bluez5-util nor module-bluez5-device files. Whole
> codec registration is done in a2dp-codec-util.c file, without need
> to update any header file.
> 
> Some A2DP codecs are bidirectional and support backchannel for
> microphone voice. This new A2DP codec API fully supports this feature
> and module-bluez5-device was extended to support microphone voice source
> for codecs which declares such support. FastStream is such codec.
> 
> For every A2DP codec is created card profile. When using bluez patches
> from https://marc.info/?l=linux-bluetooth&m=154696260401673&w=2 then
> only those profiles codec profiles are created which are supported
> by remote headset/endpoint.

As discussed before, I don't think the codec configuration should be
exposed via card profiles. There is need for being able to say "switch
to A2DP" without specifying the codec.

It's unclear how priority of the codecs (and their parameter
permutations) should be configured, but it seems quite clear that a
"set codec" operation on a specific card would be useful. If the "set
codec" operation is separate from "set profile" operation, then you no
doubt will ask how to implement the client API for this new operation,
and I don't have a very good answer.

Georg Chini has been working on a new messaging API, which would be a
good fit for this, but that's stalled (I don't remember if it's waiting
for review or a new version of the patches). If you don't want to be
blocked by that, the alternative is to add new "get bluetooth card
info" and "set bluetooth card a2dp codec" commands to the core protocol
(the card info command would be for enumerating the available codecs),
or to add the commands via a new "protocol extension" similar to what
module-stream-restore, module-device-restore and module-device-manager
do. I would be fine with either approach.

Adding new commands to the core protocol would be somewhat simpler, but
I'm not sure other maintainers are ok with adding bluetooth specific
functionality to the core protocol.

-- 
Tanu

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