Strange question, but this has been bugging me for a long time now. Sometimes when I scroll through my Twitter feed in Firefox, if a gif automatically plays (in a
<video> element, so probably .gifv), the output of Quod Libet (or Spotify) seems to get halved. I've noticed this only happens if Quod Libet isn't set to 100% in
pavucontrol. When I play a gif, no volume sliders actually move. Both Quod Libet and FireFox show up as "ALSA Plugin", so there is a chance this is a problem with ALSA.
Either way, Google is giving me nothing helpful, other than suggesting I disable
flat-volume, but that sounds more about the device output level actually changing - which is not what I'm seeing.