ao_alsa: remove old multichannel method

The "old" method (before the ALSA channel map API) used device aliases
like "surround51" to set the channel layout. The "interesting" part was
that these devices usually redirect to a hardware device. This means
playing stereo would lead you to the "default" device (dmix), while e.g.
5.1 to "surround51", which automatically takes care of the fact that
dmix can't do 5.1.

This is pretty much nonsense, though. It shouldn't depend on the damn
input media file whether the player is going to use shared access (dmix)
or exclusive access (direct hw device).

As a consequence, by default ao_alsa will do only what dmix can do. If
the user actually wants multichannel, he has to select a suitable hw
device with --audio-device. From there on, the correct speaker mapping
will be ensured via the channel mapping API.

The change is preparation for making multichannel output the default (as
far as supported by the audio output API). Of the common APIs, only ALSA
messes up beyond repair, so I feel like this change is needed.

On ancient alsa-lib versions, only stereo and mono can be played with
this branch.

1 files changed, 3 insertions, 49 deletions

diff --git a/audio/out/ao_alsa.c b/audio/out/ao_alsa.c
index af051bed4f..f3e8c8cd68 100644
--- a/audio/out/ao_alsa.c
+++ b/audio/out/ao_alsa.c
@@ -320,47 +320,6 @@ static bool query_chmaps(struct ao *ao, struct mp_chmap *chmap)
 
 #endif /* else HAVE_CHMAP_API */
 
-// Lists device names and their implied channel map.
-// The second item must be resolvable with mp_chmap_from_str().
-// Source: http://www.alsa-project.org/main/index.php/DeviceNames
-// (Speaker names are slightly different from mpv's.)
-static const char *const device_channel_layouts[][2] = {
-    {"default",         "fc"},
-    {"default",         "fl-fr"},
-    {"rear",            "bl-br"},
-    {"center_lfe",      "fc-lfe"},
-    {"side",            "sl-sr"},
-    {"surround40",      "fl-fr-bl-br"},
-    {"surround50",      "fl-fr-bl-br-fc"},
-    {"surround41",      "fl-fr-bl-br-lfe"},
-    {"surround51",      "fl-fr-bl-br-fc-lfe"},
-    {"surround71",      "fl-fr-bl-br-fc-lfe-sl-sr"},
-};
-
-#define NUM_ALSA_CHMAPS MP_ARRAY_SIZE(device_channel_layouts)
-
-static const char *select_chmap(struct ao *ao, struct mp_chmap *chmap)
-{
-    struct mp_chmap_sel sel = {0};
-    struct mp_chmap maps[NUM_ALSA_CHMAPS];
-    for (int n = 0; n < NUM_ALSA_CHMAPS; n++) {
-        mp_chmap_from_str(&maps[n], bstr0(device_channel_layouts[n][1]));
-        mp_chmap_sel_add_map(&sel, &maps[n]);
-    };
-
-    if (!ao_chmap_sel_adjust(ao, &sel, chmap))
-        return "default";
-
-    for (int n = 0; n < NUM_ALSA_CHMAPS; n++) {
-        if (mp_chmap_equals(chmap, &maps[n]))
-            return device_channel_layouts[n][0];
-    }
-
-    MP_ERR(ao, "channel layout %s (%d ch) not supported.\n",
-           mp_chmap_to_str(chmap), chmap->num);
-    return "default";
-}
-
 static int map_iec958_srate(int srate)
 {
     switch (srate) {
@@ -451,17 +410,11 @@ static int init_device(struct ao *ao)
     if (!p->cfg_ni)
         ao->format = af_fmt_from_planar(ao->format);
 
-    struct mp_chmap implied_chmap = ao->channels;
-    const char *device;
+    const char *device = "default";
     if (AF_FORMAT_IS_IEC61937(ao->format)) {
         device = "iec958";
         MP_VERBOSE(ao, "playing AC3/iec61937/iec958, %i channels\n",
                    ao->channels.num);
-    } else {
-        device = select_chmap(ao, &implied_chmap);
-        // Not-default likely means a hw device - enable software conversions.
-        if (strcmp(device, "default") != 0)
-            device = talloc_asprintf(ao, "plug:%s", device);
     }
     const char *old_dev = device;
     if (ao->device)
@@ -534,8 +487,9 @@ static int init_device(struct ao *ao)
     if (query_chmaps(ao, &dev_chmap)) {
         ao->channels = dev_chmap;
     } else {
+        // Assume only stereo and mono are supported.
+        mp_chmap_from_channels(&ao->channels, MPMIN(2, dev_chmap.num));
         dev_chmap.num = 0;
-        ao->channels = implied_chmap;
     }
 
     int num_channels = ao->channels.num;