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, 29 insertions, 5 deletions

diff --git a/audio/out/ao.c b/audio/out/ao.c
index c9d8f42b4a..0647067e50 100644
--- a/audio/out/ao.c
+++ b/audio/out/ao.c
@@ -158,7 +158,7 @@ error:
 
 static struct ao *ao_init(bool probing, struct mpv_global *global,
                           struct input_ctx *input_ctx,
-                          struct encode_lavc_context *encode_lavc_ctx,
+                          struct encode_lavc_context *encode_lavc_ctx, int flags,
                           int samplerate, int format, struct mp_chmap channels,
                           char *dev, char *name, char **args)
 {
@@ -169,6 +169,7 @@ static struct ao *ao_init(bool probing, struct mpv_global *global,
     ao->channels = channels;
     ao->format = format;
     ao->encode_lavc_ctx = encode_lavc_ctx;
+    ao->init_flags = flags;
     if (ao->driver->encode != !!ao->encode_lavc_ctx)
         goto fail;
 
@@ -190,7 +191,7 @@ static struct ao *ao_init(bool probing, struct mpv_global *global,
             snprintf(redirect, sizeof(redirect), "%s", ao->redirect);
             snprintf(rdevice, sizeof(rdevice), "%s", ao->device ? ao->device : "");
             talloc_free(ao);
-            return ao_init(probing, global, input_ctx, encode_lavc_ctx,
+            return ao_init(probing, global, input_ctx, encode_lavc_ctx, flags,
                            samplerate, format, channels, rdevice, redirect, NULL);
         }
         goto fail;
@@ -240,7 +241,7 @@ static void split_ao_device(void *tmp, char *opt, char **out_ao, char **out_dev)
 }
 
 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)
@@ -283,7 +284,7 @@ struct ao *ao_init_best(struct mpv_global *global,
         }
     }
 
-    if (ao_null_fallback) {
+    if (init_flags & AO_INIT_NULL_FALLBACK) {
         MP_TARRAY_APPEND(tmp, ao_list, ao_num,
             (struct m_obj_settings){.name = "null"});
     }
@@ -297,7 +298,7 @@ struct ao *ao_init_best(struct mpv_global *global,
             dev = pref_dev;
             mp_verbose(log, "Using preferred device '%s'\n", dev);
         }
-        ao = ao_init(probing, global, input_ctx, encode_lavc_ctx,
+        ao = ao_init(probing, global, input_ctx, encode_lavc_ctx, init_flags,
                      samplerate, format, channels, dev,
                      entry->name, entry->attribs);
         if (ao)
@@ -429,6 +430,29 @@ bool ao_chmap_sel_adjust(struct ao *ao, const struct mp_chmap_sel *s,
     return r;
 }
 
+// safe_multichannel=true behaves like ao_chmap_sel_adjust.
+// safe_multichannel=false is a helper for callers which do not support safe
+// handling of arbitrary channel layouts. If the multichannel layouts are not
+// considered "always safe" (e.g. HDMI), then allow only stereo or mono, if
+// they are part of the list in *s.
+bool ao_chmap_sel_adjust2(struct ao *ao, const struct mp_chmap_sel *s,
+                          struct mp_chmap *map, bool safe_multichannel)
+{
+    if (!safe_multichannel && (ao->init_flags & AO_INIT_SAFE_MULTICHANNEL_ONLY)) {
+        struct mp_chmap res = *map;
+        if (mp_chmap_sel_adjust(s, &res)) {
+            if (!mp_chmap_equals(&res, &(struct mp_chmap)MP_CHMAP_INIT_MONO) &&
+                !mp_chmap_equals(&res, &(struct mp_chmap)MP_CHMAP_INIT_STEREO))
+            {
+                MP_WARN(ao, "Disabling multichannel output.\n");
+                *map = (struct mp_chmap)MP_CHMAP_INIT_STEREO;
+            }
+        }
+    }
+
+    return ao_chmap_sel_adjust(ao, s, map);
+}
+
 bool ao_chmap_sel_get_def(struct ao *ao, const struct mp_chmap_sel *s,
                           struct mp_chmap *map, int num)
 {