ao_alsa: add an option to ignore ALSA channel map negotiation

This was requested, more or less.

2 files changed, 14 insertions, 2 deletions

diff --git a/DOCS/man/ao.rst b/DOCS/man/ao.rst
index fdbefbb167..60ba6348b1 100644
--- a/DOCS/man/ao.rst
+++ b/DOCS/man/ao.rst
@@ -55,6 +55,14 @@ Available audio output drivers are:
         Allow output of non-interleaved formats (if the audio decoder uses
         this format). Currently disabled by default, because some popular
         ALSA plugins are utterly broken with non-interleaved formats.
+    ``ingore-chmap``
+        Don't read or set the channel map of the ALSA device - only request the
+        required number of channels, and then pass the audio as-is to it. This
+        option most likely should not be used. It can be useful for debugging,
+        or for static setups with a specially engineered ALSA configuration (in
+        this case you should always force the same layout with ``--audio-channels``,
+        or it will work only for files which use the layout implicit to your
+        ALSA device).
 
     .. note::
 
diff --git a/audio/out/ao_alsa.c b/audio/out/ao_alsa.c
index dba6b19514..1ee662ac77 100644
--- a/audio/out/ao_alsa.c
+++ b/audio/out/ao_alsa.c
@@ -64,6 +64,7 @@ struct priv {
     int cfg_mixer_index;
     int cfg_resample;
     int cfg_ni;
+    int cfg_ignore_chmap;
 };
 
 #define BUFFER_TIME 250000  // 250ms
@@ -478,7 +479,7 @@ static int init_device(struct ao *ao)
     CHECK_ALSA_ERROR("Unable to set access type");
 
     struct mp_chmap dev_chmap = ao->channels;
-    if (AF_FORMAT_IS_IEC61937(ao->format)) {
+    if (AF_FORMAT_IS_IEC61937(ao->format) || p->cfg_ignore_chmap) {
         dev_chmap.num = 0; // disable chmap API
     } else if (query_chmaps(ao, &dev_chmap)) {
         ao->channels = dev_chmap;
@@ -571,7 +572,9 @@ static int init_device(struct ao *ao)
 
         MP_VERBOSE(ao, "which we understand as: %s\n", mp_chmap_to_str(&chmap));
 
-        if (AF_FORMAT_IS_IEC61937(ao->format)) {
+        if (p->cfg_ignore_chmap) {
+            MP_VERBOSE(ao, "user set ignore-chmap; ignoring the channel map.\n");
+        } else if (AF_FORMAT_IS_IEC61937(ao->format)) {
             MP_VERBOSE(ao, "using spdif passthrough; ignoring the channel map.\n");
         } else if (mp_chmap_is_valid(&chmap)) {
             if (mp_chmap_equals(&chmap, &ao->channels)) {
@@ -934,6 +937,7 @@ const struct ao_driver audio_out_alsa = {
         OPT_STRING("mixer-name", cfg_mixer_name, 0),
         OPT_INTRANGE("mixer-index", cfg_mixer_index, 0, 0, 99),
         OPT_FLAG("non-interleaved", cfg_ni, 0),
+        OPT_FLAG("ignore-chmap", cfg_ignore_chmap, 0),
         {0}
     },
 };