Bluetooth: mSBC playback does not work with headsets Soundcore Life P2 and AXLOI Goin
Bluetooth: mSBC playback does not work
TLDR: Long thread, a lot of things tested. @pvir has a confirmed-good setup with the same bluetooth adapter+kernel+patches with other headsets, so the most likely explanation is a problem with the headsets (and most likely in combination with a bluetooth-over-usb adapter)
System Setup
- Ubuntu 20.04 / Linux version 5.4.0-60-generic
- Built-in USB bluetooth adapter (USB ID 8087:07dc Intel Corp.)
- Headset Soundcore Life P2-L
- Headset AXLOIE Goin
- Pipewire with backend-native
Observation:
- After enabling mSBC in config, audio playback on HFP does not work, only play's silence
Expected behaviour:
- Have good audio
Analysis:
Similar to #549 (closed), all-zero packets (i.e. 48 zeros in the packet) get inserted into the packet stream which do not have anything to do with the payload data stream. This can be observed via sudo btmon -S
Some background can be found here
Because the mtu is 48 and the mSBC encode size is 60, the transmission stops after 48 bytes, we now wait for a new mSBC packet to be received, so we miss the next eSCO transmission window and the headset fills in with zeros causing the packet to be chopped and the next one to be discarded as invalid.
Conclusion The Intel USB bluetooth adapter 8087:07dc is confirmed working with a Kernel 5.9 + patch (see below).
Other headsets are confirmed working with (thank you for testing, @pvir)
Ubuntu 20.04 + 5.8.0-36-generic hwe kernel + out-of-tree drivers/bluetooth @ 517b693351a2d, pipewire at b3213bcb(sco-accounting), adapter Intel 8087:07dc