audio: add channel map selection function

The point is selecting a minimal fallback. The AOs will call this
through the AO API, so it will be possible to add options affecting
the general channel layout selection.

It provides the following mechanism to AOs:
- forcing the correct channel order
- downmixing to stereo if no layout is available
- allow 5.1 <-> 5.1(side) fallback
- handling "unknown" channel layouts

This is quite weak and lots of code/complexity for little gain. All AOs
already made sure the channel order was correct, and the fallback is of
little value, and could perhaps be done in the frontend instead, like
stereo downmixing with --channels=2 is handled. But I'm not really sure
how this stuff should _really_ work, and the new code will hopefully
provides enough flexibility to make radical changes to channel layout
negotiation easier.

1 files changed, 1 insertions, 2 deletions

diff --git a/audio/audio.c b/audio/audio.c
index 8af6a20a1f..c9d5c9231c 100644
--- a/audio/audio.c
+++ b/audio/audio.c
@@ -37,8 +37,7 @@ void mp_audio_set_num_channels(struct mp_audio *mpa, int num_channels)
 void mp_audio_set_channels_old(struct mp_audio *mpa, int num_channels)
 {
     struct mp_chmap map;
-    mp_chmap_from_channels(&map, num_channels);
-    mp_chmap_reorder_to_alsa(&map);
+    mp_chmap_from_channels_alsa(&map, num_channels);
     mp_audio_set_channels(mpa, &map);
 }