[pulseaudio-discuss] Possible to sync multiple sinks when using raop

[Marshall Eubanks]

I’ve managed to get raop working with the devices I have on hand (I’m using Sayonara Player for playback), and I can even play on multiple sinks using the pulseaudio module module-combine-sink.

However, unsurprisingly this fails to sync between the local sink and the raop sink. 

I noticed this bit in the release notes:

Much more accurate latency reporting for AirPlay devices
The AirPlay protocol has a large latency, but PulseAudio didn't previously report that latency to applications. Now it reports it, or at least something much closer to the reality than before.

The AirPlay protocol doesn't provide a mechanism for getting the exact latency (or if it does, we're not aware of that). PulseAudio makes an educated guess, and a significant part of that guess is a latency constant that is added to each latency report. The default value for that constant is exactly 2 seconds, but that's not optimal for all devices. PulseAudio uses a different constant for some known devices, and we'd like to expand the set of known devices. If you find that audio-video synchronization is bad with your AirPlay device, you can experiment with different latency constants by passing argument "latency_msec=2000" to module-raop-discover in /etc/pulse/default.pa. Change the number 2000 to something that works better. Once you find a better latency value, we'd be happy hear from you so that we can add your device to the list of known devices.

Which makes me think there has been some attempt to make sync possible. Yet it seems pulseaudio is ignoring its own latency reporting! When I press play/pause in my player, the output immediately ceases on the local sync, and I have to wait the 2 seconds for it to propagate to the raop device (as expected). 

Is there a way to get what I want? Am I going about it complety wrong?

Marshall Eubanks
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