[pulseaudio-discuss] Output PA streams to two sinks simultaneously

[tieg]

Hi, 

A typical case for PA is to output streams from two or more sinks at the
same time. PA provides a special module to handle this case --
module-combine.

Let's analyze a case on mobile phone.
Mobile phone have two sinks, one sink for embedded speaker, one sink for
BT headphone.
When call is coming, ringtone should be played. The rule for ringtone
is:
1. if no BT headphone, ringtone will out from speaker.
2. if BT headphone is paired, ringtone will out from speaker and BT
headphone.

At first, BT headphone is not paired, so ringtone will be direct to sink
for speaker. Then BT headphone is paired when ringtone is playing, and
ringtone should output from speaker and BT. For such situation,
module-combine should be used. As we know, after a lot of very
complicated steps, ringtone can out from two devices.

The issue of above process is :
1. Heavy work
Module-combine is complicated and heavy. To make module-combine work
correctly, you need to do preparation or initialization before stream
flow to dest sinks. In the running stage, module-combine will bring some
delay between input streams and dest sinks.
2. Performance & Power
module-combine will introduce performance issue and power issue.
Performance and power are key concern points for mobile phone.
2. Audio Quality
Switching is needed between sinks. Thus the audio quality will be
impacted.

Is there any good/light method to handle above BT scenario?

BR
tieg