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bluetooth: Update source software volume on AVRCP SetAbsoluteVolume

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The A2DP spec mandates that the audio rendering device - the device
receiving audio, in our case a `pa_source` - is responsible for
performing attenuation:

AVRCP v1.6.2, §5.8:
    The SetAbsoluteVolume command is used to set an absolute volume to be used by the rendering device.

BlueZ models this call as a change of the `Volume` property on the
`org.bluez.MediaTransport1` interface.  Supporting Absolute Volume is
optional but BlueZ unconditionally reports feature category 2 in its
profile, mandating support.  Hence remote devices (ie. a phone) playing
back audio to a machine running PulseAudio assume volume is to be
changed through SetAbsoluteVolume, without performing any local
attenuation.

Future changes will implement this feature the other way around: setting
an initial value for the `Volume` property as well as propagating
`pa_source` volume changes back to the peer.

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/239>
This commit is contained in:
Marijn Suijten 2021-03-27 10:53:07 +01:00 • committed by PulseAudio Marge Bot
parent c098a75d10
commit 710a35cdc3
2 changed files with 45 additions and 0 deletions
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1
src/modules/bluetooth/bluez5-util.h
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@ -52,6 +52,7 @@
#define PA_BLUETOOTH_UUID_HFP_HF "0000111e-0000-1000-8000-00805f9b34fb"
#define PA_BLUETOOTH_UUID_HFP_AG "0000111f-0000-1000-8000-00805f9b34fb"
#define A2DP_MAX_GAIN 127
#define HSP_MAX_GAIN 15
typedef struct pa_bluetooth_transport pa_bluetooth_transport;