Comment 190 for bug 405294

Created attachment 125291
Proof-of-concept patch

I've solved this issue for myself - I've been using pulseaudio with my changes for several months now with no major problems.

I've noticed that every time signal degrades audio gets more out of sync - up to about 10-15 seconds (if I remember correctly).

I've debugged bluez5 pulseaudio module and suspect that the problem lies in buffering for bluetooth socket. Here's my analysis:

1) Pulseaudio detects BT signal drop when write() on bluetooth socket returns EAGAIN (i.e., when the buffer is full).
2) Bluetooth socket buffer is quite big (by default)
3) When pulseaudio stops sending audio packets to BT socket the buffer still contains a lot of packets
4) pulseaudio considers those packets as successfully sent - but they aren't
5) BT connection seems to never be able to "catch up" with the amount of buffered packets and audio becomes out-of-sync.

So here's my patch. The main change is to decrease the buffer size as much as possible. I've experimented and found out that settings buffer size to 2x-5x of packet size works best for me. This ensures that audio lag won't accumulate after BT signal degradation while preventing audio skipping due to buffer underruns. Audio still may skip (sometimes several times in a row) - but without the lag after BT signal restores.

Unfortunately with this patch bluetooth microphone (headset profile) won't work - since I don't use one and couldn't test it. I hope that someone would be able to pick it up and make into a form that would be possible to merge in master branch.

The changes are contained in attached path on github: https://github.com/dmitryvk/pulseaudio/commit/12b13c75d3a9b377e0f7de7c86116e3af41ce5ee. Patch was developed against Pulseaudio-8.0 but it works with Pulseaudio-9.0.