audio/out: reduce amount of audio buffering

Since the addition of the AO feed thread, 200ms of latency (MIN_BUFFER)
was added to all push-based AOs. This is not so nice, because even AOs
with relatively small buffering (e.g. ao_alsa on my system with ~170ms
of buffer size), the additional latency becomes noticable when e.g.
toggling mute with softvol.

Fix this by trying to keep not only 200ms minimum buffer, but also 200ms
maximum buffer. In other words, never buffer beyond 200ms in total. Do
this by estimating the AO's buffer fill status using get_space and the
initially known AO buffer size (the get_space return value on
initialization, before any audio was played). We limit the maximum
amount of data written to the soft buffer so that soft buffer size and
audio buffer size equal to 200ms (MIN_BUFFER).

To avoid weird problems with weird AOs, we buffer beyond MIN_BUFFER if
the AO's get_space requests more data than that, and as long as the soft
buffer is large enough.

Note that this is just a hack to improve the latency. When the audio
chain gains the ability to refilter data, this won't be needed anymore,
and instead we can introduce some sort of buffer replacement function in
order to update data in the soft buffer.

1 files changed, 0 insertions, 3 deletions

diff --git a/audio/out/ao.c b/audio/out/ao.c
index ee8bc2a254..d48b266122 100644
--- a/audio/out/ao.c
+++ b/audio/out/ao.c
@@ -36,9 +36,6 @@
 #include "common/common.h"
 #include "common/global.h"
 
-// Minimum buffer size in seconds.
-#define MIN_BUFFER 0.2
-
 extern const struct ao_driver audio_out_oss;
 extern const struct ao_driver audio_out_coreaudio;
 extern const struct ao_driver audio_out_rsound;