Merge pull request #76541 from KoBeWi/WAZZUP

Add mono audio support to WASAPI

drivers/wasapi/audio_driver_wasapi.cpp

@@ -480,6 +480,14 @@ Error AudioDriverWASAPI::init_output_device(bool p_reinit) {
 	}
 
 	switch (audio_output.channels) {
+		case 1: // Mono
+		case 3: // Surround 2.1
+		case 5: // Surround 5.0
+		case 7: // Surround 7.0
+			// We will downmix as required.
+			channels = audio_output.channels + 1;
+			break;
+
 		case 2: // Stereo
 		case 4: // Surround 3.1
 		case 6: // Surround 5.1
@@ -499,7 +507,7 @@ Error AudioDriverWASAPI::init_output_device(bool p_reinit) {
 	input_position = 0;
 	input_size = 0;
 
-	print_verbose("WASAPI: detected " + itos(channels) + " channels");
+	print_verbose("WASAPI: detected " + itos(audio_output.channels) + " channels");
 	print_verbose("WASAPI: audio buffer frames: " + itos(buffer_frames) + " calculated latency: " + itos(buffer_frames * 1000 / mix_rate) + "ms");
 
 	return OK;
@@ -746,6 +754,19 @@ void AudioDriverWASAPI::thread_func(void *p_udata) {
 							for (unsigned int i = 0; i < write_frames * ad->channels; i++) {
 								ad->write_sample(ad->audio_output.format_tag, ad->audio_output.bits_per_sample, buffer, i, ad->samples_in.write[write_ofs++]);
 							}
+						} else if (ad->channels == ad->audio_output.channels + 1) {
+							// Pass all channels except the last two as-is, and then mix the last two
+							// together as one channel. E.g. stereo -> mono, or 3.1 -> 2.1.
+							unsigned int last_chan = ad->audio_output.channels - 1;
+							for (unsigned int i = 0; i < write_frames; i++) {
+								for (unsigned int j = 0; j < last_chan; j++) {
+									ad->write_sample(ad->audio_output.format_tag, ad->audio_output.bits_per_sample, buffer, i * ad->audio_output.channels + j, ad->samples_in.write[write_ofs++]);
+								}
+								int32_t l = ad->samples_in.write[write_ofs++];
+								int32_t r = ad->samples_in.write[write_ofs++];
+								int32_t c = (int32_t)(((int64_t)l + (int64_t)r) / 2);
+								ad->write_sample(ad->audio_output.format_tag, ad->audio_output.bits_per_sample, buffer, i * ad->audio_output.channels + last_chan, c);
+							}
 						} else {
 							for (unsigned int i = 0; i < write_frames; i++) {
 								for (unsigned int j = 0; j < MIN(ad->channels, ad->audio_output.channels); j++) {