[pulseaudio-tickets] [Bug 58746] bluetooth audio out of sync when connection temporarily drops

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=58746

--- Comment #14 from paco3346 at gmail.com ---
(In reply to Dmitry Kalyanov from comment #8)
> Created attachment 125291 [details] [review]
> 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.

Genius! I understand the problems with this patch but for now it's music to my
ears (pun intended). Using on Arch with Pulseaudio 9.

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