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

[Georg Chini]

On 23.02.20 12:16, Daniel Krysiak wrote:
> 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)

What PA version are you using?