Hi all, I was looking into, so called, absolute volume control that was introduced in AVRCP v1.4. What I want to achieve is to send audio from android smartphone to linux based device running bluez and make the volume control on the smartphone side to control the volume on the device. So the device is the a2dp sink + avrcp CT/TG and the phone is a2dp source + avrcp CT/TG. I assume that if all is working correctly then on the dbus the Volume property of the org.bluez.MediaTransport1 will be changed by the volume control of the phone and changes made to this property from the device would propagate to the phone volume slider. This is not happening and what I believe is the cause is that AVRCP_EVENT_VOLUME_CHANGED event registration request sent from the phone is rejected by the bluez. I can see that on the wireshark snoop from the device's bluetooth adapter. And on wireshark I see that AVRCP_EVENT_VOLUME_CHANGED event registration is sent by the phone before bluez initializes session->supported_events variable (not really sure about that). I think that this rejection makes the phone to not send SetAbsoluteVolume commands to the device on volume change. To test my theory i changed the session_init_control function in the profiles/audio/avrcp.c to call first target_init and then controller_init. This caused the AVRCP_EVENT_VOLUME_CHANGED event not been rejected and the volume control from the phone works as expected. After reading AVRCP specification I did not find any reason for the CT on the phone side not to send event registration immediately after the AVCTP connection establishment. So I believe that bluez should not reject event registration in this case. Best Regards, Marek Czerski
