coreaudio-encoder: Surround sound improvements

The core audio aac encoder has bitrates maps specific to speaker
layouts.  Previously, the bitrate map maxed at 320 kbs and was the map
for stereo.  The bitrate map is now tailored to the speaker layout.  In
practice this unlocks higher bitrates.  For instance up to 960 kbs for
7.1.  Additionally the commit fixes a bug with 2.1 with channels not
ordered correctly.

plugins/coreaudio-encoder/encoder.cpp

@@ -546,7 +546,7 @@ static void *aac_create(obs_data_t *settings, obs_encoder_t *encoder)
 
 	UInt32 rate_control = kAudioCodecBitRateControlMode_Constant;
 
-	if (obs_data_get_bool(settings, "allow he-aac")) {
+	if (obs_data_get_bool(settings, "allow he-aac") && ca->channels != 3) {
 		ca->allowed_formats = &aac_formats;
 	} else {
 		ca->allowed_formats = &aac_lc_formats;
@@ -603,9 +603,15 @@ static void *aac_create(obs_data_t *settings, obs_encoder_t *encoder)
 
 	/*
 	 * Fix channel map differences between CoreAudio AAC, FFmpeg, Wav
-	 * New channel mappings below assume 4.1, 5.1, 7.1 resp.
+	 * New channel mappings below assume 2.1, 4.1, 5.1, 7.1 resp.
 	 */
-	if (ca->channels == 5) {
+	if (ca->channels == 3) {
+		SInt32 channelMap3[3] = {2, 0, 1};
+		AudioConverterSetProperty(ca->converter,
+				kAudioConverterChannelMap,
+				sizeof(channelMap3), channelMap3);
+
+	} else if (ca->channels == 5) {
 		SInt32 channelMap5[5] = {2, 0, 1, 3, 4};
 		AudioConverterSetProperty(ca->converter,
 				kAudioConverterChannelMap,
@@ -900,10 +906,9 @@ static bool aac_extra_data(void *data, uint8_t **extra_data, size_t *size)
 }
 
 static asbd_builder fill_common_asbd_fields(asbd_builder builder,
-		bool in=false)
+		bool in=false, UInt32 channels=2)
 {
-	UInt32 bytes_per_frame = 8;
-	UInt32 channels = 2;
+	UInt32 bytes_per_frame = sizeof(float) * channels;
 	UInt32 bits_per_channel = bytes_per_frame / channels * 8;
 
 	builder.channels_per_frame(channels);
@@ -931,9 +936,9 @@ static AudioStreamBasicDescription get_default_in_asbd()
 		.asbd;
 }
 
-static asbd_builder get_default_out_asbd_builder()
+static asbd_builder get_default_out_asbd_builder(UInt32 channels)
 {
-	return fill_common_asbd_fields(asbd_builder())
+	return fill_common_asbd_fields(asbd_builder(), false, channels)
 		.sample_rate(44100);
 }
 
@@ -998,7 +1003,7 @@ static bool find_best_match(DStr &log, ca_encoder *ca, UInt32 bitrate,
 		log_to_dstr(log, ca, "Trying %s (0x%x)\n",
 				format_id_to_str(format_id), format_id);
 
-		auto out = get_default_out_asbd_builder()
+		auto out = get_default_out_asbd_builder(2)
 			.format_id(format_id)
 			.asbd;
 
@@ -1229,6 +1234,11 @@ static vector<UInt32> get_bitrates(DStr &log, ca_encoder *ca,
 		Float64 samplerate)
 {
 	vector<UInt32> bitrates;
+	struct obs_audio_info aoi;
+	int channels;
+
+	obs_get_audio_info(&aoi);
+	channels = get_audio_channels(aoi.speakers);
 
 	auto handle_bitrate = [&](UInt32 bitrate)
 	{
@@ -1263,7 +1273,7 @@ static vector<UInt32> get_bitrates(DStr &log, ca_encoder *ca,
 				static_cast<uint32_t>(format_id),
 				samplerate);
 
-		auto out = get_default_out_asbd_builder()
+		auto out = get_default_out_asbd_builder(channels)
 			.format_id(format_id)
 			.sample_rate(samplerate)
 			.asbd;