[pulseaudio-discuss] Latency problem with module-loopback after downtime

[Daniel Krysiak]

Hi,

No, this is not about the usual loopback latency ;) I have found a 
strange anomaly.

I have 2 sound cards: C-Media CMI8738 (I've check, well supported on 
Linux, work great)
1st is for Toslink input, 2nd for Toslink output (and this is the 
default and only sink for the whole system)

I'm setting up a loopback device like this:
pactl load-module module-loopback \
latency_msec=1 \
source=alsa_input.pci-0000_06_01.0.iec958-stereo \
sink=alsa_output.pci-0000_06_02.0.iec958-stereo

And this works great! Latency is very low:
Sink Input #0
         Driver: module-loopback.c
         [...]
         Buffer Latency: 10250 usec
         Sink Latency: 7263 usec

Source Output #0
         Driver: module-loopback.c
         [...]
         Buffer Latency: 0 usec
         Source Latency: 380 usec


Now, here is the problem. When I unplug a cable of the source, source 
latency rises to infinity. And I understand why, it's fine, but, when I 
plug the cable again, then: source Latency slowly goes down, but sink's 
buffer latency rises, up to even 8-12 seconds.

Notes:
  - Reloading the module is a fix.
  - by unplug I mean unplug, or shut down the source: anything that 
stops the signal.


What I'm looking for:
1. This is most likely a bug, which I could help analyze by providing 
more data.
2. But in the meantime, I'm looking for a way to reload the module when 
source device shows up. This is the best I came up with so far, in tmux:

watch -n 105 'pactl list | grep -A 12 module-loopback.c | grep "Source 
Latency" | grep -Eo "[0-9]{9}" &> /dev/null && pactl unload-module 
module-loopback && sleep 6 && pactl load-module module-loopback 
latency_msec=1 source=alsa_input.pci-0000_06_01.0.iec958-stereo 
sink=alsa_output.pci-0000_06_02.0.iec958-stereo && echo "reload"'

(if Source Latency goes over 8 digit number (100seconds), reload the 
module-loopback)
-- 
dextkrk