ao_coreaudio_utils: add function for ASBD -> mp format lookup

Useful with some of the following commits.

ca_fill_asbd() should behave exactly as before.

Instead of actually implementing the inverse function of ca_fill_asbd(),
just loop over the (small) list of mpv functions and check if any mpv
equivalent to a given ASBD exists.

audio/out/ao_coreaudio_utils.c

@@ -167,20 +167,21 @@ bool check_ca_st(struct ao *ao, int level, OSStatus code, const char *message)
     return false;
 }
 
-void ca_fill_asbd(struct ao *ao, AudioStreamBasicDescription *asbd)
+static void ca_fill_asbd_raw(AudioStreamBasicDescription *asbd, int mp_format,
+                             int samplerate, int num_channels)
 {
-    asbd->mSampleRate       = ao->samplerate;
+    asbd->mSampleRate       = samplerate;
     // Set "AC3" for other spdif formats too - unknown if that works.
-    asbd->mFormatID         = AF_FORMAT_IS_IEC61937(ao->format) ?
+    asbd->mFormatID         = AF_FORMAT_IS_IEC61937(mp_format) ?
                               kAudioFormat60958AC3 :
                               kAudioFormatLinearPCM;
-    asbd->mChannelsPerFrame = ao->channels.num;
-    asbd->mBitsPerChannel   = af_fmt2bits(ao->format);
+    asbd->mChannelsPerFrame = num_channels;
+    asbd->mBitsPerChannel   = af_fmt2bits(mp_format);
     asbd->mFormatFlags      = kAudioFormatFlagIsPacked;
 
-    if ((ao->format & AF_FORMAT_TYPE_MASK) == AF_FORMAT_F) {
+    if ((mp_format & AF_FORMAT_TYPE_MASK) == AF_FORMAT_F) {
         asbd->mFormatFlags |= kAudioFormatFlagIsFloat;
-    } else if ((ao->format & AF_FORMAT_SIGN_MASK) == AF_FORMAT_SI) {
+    } else if ((mp_format & AF_FORMAT_SIGN_MASK) == AF_FORMAT_SI) {
         asbd->mFormatFlags |= kAudioFormatFlagIsSignedInteger;
     }
 
@@ -193,6 +194,54 @@ void ca_fill_asbd(struct ao *ao, AudioStreamBasicDescription *asbd)
         (asbd->mBitsPerChannel / 8);
 }
 
+void ca_fill_asbd(struct ao *ao, AudioStreamBasicDescription *asbd)
+{
+    ca_fill_asbd_raw(asbd, ao->format, ao->samplerate, ao->channels.num);
+}
+
+static bool ca_formatid_is_digital(uint32_t formatid)
+{
+    switch (formatid)
+    case 'IAC3':
+    case 'iac3':
+    case  kAudioFormat60958AC3:
+    case  kAudioFormatAC3:
+        return true;
+    return false;
+}
+
+// This might be wrong, but for now it's sufficient for us.
+static uint32_t ca_normalize_formatid(uint32_t formatID)
+{
+    return ca_formatid_is_digital(formatID) ? kAudioFormat60958AC3 : formatID;
+}
+
+bool ca_asbd_equals(const AudioStreamBasicDescription *a,
+                    const AudioStreamBasicDescription *b)
+{
+    int flags = kAudioFormatFlagIsPacked | kAudioFormatFlagIsFloat |
+            kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsBigEndian;
+
+    return (a->mFormatFlags & flags) == (b->mFormatFlags & flags) &&
+           a->mBitsPerChannel == b->mBitsPerChannel &&
+           ca_normalize_formatid(a->mFormatID) ==
+                ca_normalize_formatid(b->mFormatID) &&
+           a->mBytesPerPacket == b->mBytesPerPacket;
+}
+
+// Return the AF_FORMAT_* (AF_FORMAT_S16 etc.) corresponding to the asbd.
+int ca_asbd_to_mp_format(const AudioStreamBasicDescription *asbd)
+{
+    for (int n = 0; af_fmtstr_table[n].format; n++) {
+        int mp_format = af_fmtstr_table[n].format;
+        AudioStreamBasicDescription mp_asbd = {0};
+        ca_fill_asbd_raw(&mp_asbd, mp_format, 0, asbd->mChannelsPerFrame);
+        if (ca_asbd_equals(&mp_asbd, asbd))
+            return mp_format;
+    }
+    return 0;
+}
+
 void ca_print_asbd(struct ao *ao, const char *description,
                    const AudioStreamBasicDescription *asbd)
 {

audio/out/ao_coreaudio_utils.h

@@ -55,6 +55,9 @@ OSStatus ca_select_device(struct ao *ao, char* name, AudioDeviceID *device);
 void ca_fill_asbd(struct ao *ao, AudioStreamBasicDescription *asbd);
 void ca_print_asbd(struct ao *ao, const char *description,
                    const AudioStreamBasicDescription *asbd);
+bool ca_asbd_equals(const AudioStreamBasicDescription *a,
+                    const AudioStreamBasicDescription *b);
+int ca_asbd_to_mp_format(const AudioStreamBasicDescription *asbd);
 
 int64_t ca_frames_to_us(struct ao *ao, uint32_t frames);
 int64_t ca_get_latency(const AudioTimeStamp *ts);