audio: remove UNKNOWN pseudo speakers

Reuse MP_SPEAKER_ID_NA for this. If all mp_chmap entries are set to NA,
the channel layout has special "unknown channel layout" semantics, which
are used to deal with some corner cases.

(cherry picked from commit 55e777f10b)

audio/chmap.c

@@ -144,12 +144,10 @@ bool mp_chmap_is_empty(const struct mp_chmap *src)
 bool mp_chmap_is_unknown(const struct mp_chmap *src)
 {
     for (int n = 0; n < src->num; n++) {
-        int speaker = src->speaker[n];
-        if (speaker >= MP_SPEAKER_ID_UNKNOWN0 &&
-            speaker <= MP_SPEAKER_ID_UNKNOWN_LAST)
-            return true;
+        if (src->speaker[n] != MP_SPEAKER_ID_NA)
+            return false;
     }
-    return false;
+    return mp_chmap_is_valid(src);
 }
 
 // Note: empty channel maps compare as equal. Invalid ones can equal too.
@@ -240,6 +238,8 @@ void mp_chmap_from_channels_alsa(struct mp_chmap *dst, int num_channels)
 // Set *dst to an unknown layout for the given numbers of channels.
 // If the number of channels is invalid, an invalid map is set, and
 // mp_chmap_is_valid(dst) will return false.
+// A mp_chmap with all entries set to NA is treated specially in some
+// contexts (watch out for mp_chmap_is_unknown()).
 void mp_chmap_set_unknown(struct mp_chmap *dst, int num_channels)
 {
     if (num_channels < 0 || num_channels > MP_NUM_CHANNELS) {
@@ -247,7 +247,7 @@ void mp_chmap_set_unknown(struct mp_chmap *dst, int num_channels)
     } else {
         dst->num = num_channels;
         for (int n = 0; n < dst->num; n++)
-            dst->speaker[n] = MP_SPEAKER_ID_UNKNOWN0 + n;
+            dst->speaker[n] = MP_SPEAKER_ID_NA;
     }
 }
 

audio/chmap.h

@@ -56,15 +56,12 @@ enum mp_speaker_id {
     MP_SPEAKER_ID_SDR,          // SURROUND_DIRECT_RIGHT
     MP_SPEAKER_ID_LFE2,         // LOW_FREQUENCY_2
 
-    // Special mpv-specific speaker entries reserved for channels which have no
-    // known meaning.
-    MP_SPEAKER_ID_UNKNOWN0 = 64,
-    MP_SPEAKER_ID_UNKNOWN_LAST = MP_SPEAKER_ID_UNKNOWN0 + MP_NUM_CHANNELS - 1,
+    // Speaker IDs >= 64 are not representable in WAVEFORMATEXTENSIBLE or libav*.
 
     // "Silent" channels. These are sometimes used to insert padding for
     // unused channels. Unlike other speaker types, multiple of these can
     // occur in a single mp_chmap.
-    MP_SPEAKER_ID_NA,
+    MP_SPEAKER_ID_NA = 64,
 
     // Including the unassigned IDs in between. This is not a valid ID anymore,
     // but is still within uint8_t.

test/chmap_sel.c

@@ -89,9 +89,7 @@ static void test_mp_chmap_sel_fallback_reject_unknown(void **state) {
     struct mp_chmap b;
     struct mp_chmap_sel s = {0};
 
-    a.num = 2;
-    a.speaker[0] = MP_SPEAKER_ID_UNKNOWN0;
-    a.speaker[1] = MP_SPEAKER_ID_UNKNOWN0 + 1;
+    mp_chmap_set_unknown(&a, 2);
 
     mp_chmap_from_str(&b, bstr0("5.1"));