audio: use --audio-channels=auto behavior, except on ALSA

This commit adds an --audio-channel=auto-safe mode, and makes it the
default. This mode behaves like "auto" with most AOs, except with
ao_alsa. The intention is to allow multichannel output by default on
sane APIs. ALSA is not sane as in it's so low level that it will e.g.
configure any layout over HDMI, even if the connected A/V receiver does
not support it. The HDMI fuckup is of course not ALSA's fault, but other
audio APIs normally isolate applications from dealing with this and
require the user to globally configure the correct output layout.

This will help with other AOs too. ao_lavc (encoding) is changed to the
new semantics as well, because it used to force stereo (perhaps because
encoding mode is supposed to produce safe files for crap devices?).
Exclusive mode output on Windows might need to be adjusted accordingly,
as it grants the same kind of low level access as ALSA (requires more
research).

In addition to the things mentioned above, the --audio-channels option
is extended to accept a set of channel layouts. This is supposed to be
the correct way to configure mpv ALSA multichannel output. You need to
put a list of channel layouts that your A/V receiver supports.

1 files changed, 9 insertions, 1 deletions

diff --git a/audio/out/ao.h b/audio/out/ao.h
index e8e64e33eb..3c16cef0e5 100644
--- a/audio/out/ao.h
+++ b/audio/out/ao.h
@@ -50,6 +50,14 @@ enum {
     AO_EVENT_HOTPLUG = 2,
 };
 
+enum {
+    // Allow falling back to ao_null if nothing else works.
+    AO_INIT_NULL_FALLBACK = 1 << 0,
+    // Only accept multichannel configurations that are guaranteed to work
+    // (i.e. not sending arbitrary layouts over HDMI).
+    AO_INIT_SAFE_MULTICHANNEL_ONLY = 1 << 1,
+};
+
 typedef struct ao_control_vol {
     float left;
     float right;
@@ -72,7 +80,7 @@ struct encode_lavc_context;
 struct mp_audio;
 
 struct ao *ao_init_best(struct mpv_global *global,
-                        bool ao_null_fallback,
+                        int init_flags,
                         struct input_ctx *input_ctx,
                         struct encode_lavc_context *encode_lavc_ctx,
                         int samplerate, int format, struct mp_chmap channels);