audio/out: feed AOs from a separate thread

This has 2 goals:
- Ensure that AOs have always enough data, even if the device buffers
  are very small.
- Reduce complexity in some AOs, which do their own buffering.

One disadvantage is that performance is slightly reduced due to more
copying.

Implementation-wise, we don't change ao.c much, and instead "redirect"
the driver's callback to an API wrapper in push.c.

Additionally, we add code for dealing with AOs that have a pull API.
These AOs usually do their own buffering (jack, coreaudio, portaudio),
and adding a thread is basically a waste. The code in pull.c manages
a ringbuffer, and allows callback-based AOs to read data directly.

1 files changed, 2 insertions, 0 deletions

diff --git a/wscript_build.py b/wscript_build.py
index 2d24a4c685..999a14495a 100644
--- a/wscript_build.py
+++ b/wscript_build.py
@@ -145,6 +145,8 @@ def build(ctx):
         ( "audio/out/ao_sdl.c",                  "sdl2" ),
         ( "audio/out/ao_sndio.c",                "sndio" ),
         ( "audio/out/ao_wasapi.c",               "wasapi" ),
+        ( "audio/out/pull.c" ),
+        ( "audio/out/push.c" ),
 
         ## Bstr
         ( "bstr/bstr.c" ),