mixer: prefer AO softvol control over volume filter

This partially reverts earlier decisions, when I thought it would
always be better to prefer the audio volume filter over the AO's,
because the AO's relies on the underlying audio-API, which could
be broken or exhibit unusual behavior (like it happened with ao_dsound).

However, since the audio buffer can be quite large (500 ms), and we
don't attempt to flush & refilter the audio on volume changes, always
prefer AO volume control (as long as the AO mixer doesn't control the
system mixer).

Also document what the mixer.c related AO fields mean (hopefully not
too brief).

1 files changed, 1 insertions, 0 deletions

diff --git a/audio/mixer.c b/audio/mixer.c
index bdcb0cbc5c..d97391cf7e 100644
--- a/audio/mixer.c
+++ b/audio/mixer.c
@@ -34,6 +34,7 @@ static void checkvolume(struct mixer *mixer)
 
     if (mixer->softvol == SOFTVOL_AUTO) {
         mixer->softvol = mixer->ao->per_application_mixer
+                         || mixer->ao->no_persistent_volume
                          ? SOFTVOL_NO : SOFTVOL_YES;
     }