output/openal: auto-fallback to mono if channel count is unsupported

NEWS

@@ -10,6 +10,8 @@ ver 0.16.5 (2010/??/??)
   - ffmpeg: higher precision timestamps
   - ffmpeg: don't require key frame for seeking
   - fix CUE track seeking
+* output:
+  - openal: auto-fallback to mono if channel count is unsupported
 * player:
   - make seeking to CUE track more reliable
   - the "seek" command works when MPD is stopped

src/output/openal_plugin.c

@@ -64,26 +64,26 @@ openal_audio_format(struct audio_format *audio_format)
 			return AL_FORMAT_STEREO16;
 		if (audio_format->channels == 1)
 			return AL_FORMAT_MONO16;
-		break;
+
+		/* fall back to mono */
+		audio_format->channels = 1;
+		return openal_audio_format(audio_format);
 
 	case SAMPLE_FORMAT_S8:
 		if (audio_format->channels == 2)
 			return AL_FORMAT_STEREO8;
 		if (audio_format->channels == 1)
 			return AL_FORMAT_MONO8;
-		break;
+
+		/* fall back to mono */
+		audio_format->channels = 1;
+		return openal_audio_format(audio_format);
 
 	default:
 		/* fall back to 16 bit */
 		audio_format->format = SAMPLE_FORMAT_S16;
-		if (audio_format->channels == 2)
-			return AL_FORMAT_STEREO16;
-		if (audio_format->channels == 1)
-			return AL_FORMAT_MONO16;
-		break;
+		return openal_audio_format(audio_format);
 	}
-
-	return 0;
 }
 
 static bool