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, 43 insertions, 0 deletions

diff --git a/audio/chmap_sel.h b/audio/chmap_sel.h
new file mode 100644
index 0000000000..c9d75196a5
--- /dev/null
+++ b/audio/chmap_sel.h
@@ -0,0 +1,43 @@
+/*
+ * This file is part of mpv.
+ *
+ * mpv is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * mpv is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with mpv.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef MP_CHMAP_SEL_H
+#define MP_CHMAP_SEL_H
+
+#include <stdbool.h>
+
+#include "chmap.h"
+
+struct mp_chmap_sel {
+    // should be considered opaque
+    bool allow_any, allow_waveext;
+    bool speakers[MP_SPEAKER_ID_COUNT];
+    struct mp_chmap chmaps[20];
+    int num_chmaps;
+};
+
+void mp_chmap_sel_add_any(struct mp_chmap_sel *s);
+void mp_chmap_sel_add_waveext(struct mp_chmap_sel *s);
+void mp_chmap_sel_add_waveext_def(struct mp_chmap_sel *s);
+void mp_chmap_sel_add_alsa_def(struct mp_chmap_sel *s);
+void mp_chmap_sel_add_map(struct mp_chmap_sel *s, const struct mp_chmap *map);
+void mp_chmap_sel_add_speaker(struct mp_chmap_sel *s, int id);
+bool mp_chmap_sel_adjust(const struct mp_chmap_sel *s, struct mp_chmap *map);
+bool mp_chmap_sel_get_def(const struct mp_chmap_sel *s, struct mp_chmap *map,
+                          int num);
+
+#endif