SDL: Allow selecting the audio channel count from the command line

backends/mixer/sdl/sdl-mixer.cpp

@@ -73,7 +73,7 @@ void SdlMixerManager::init() {
 		warning("Could not open audio device: %s", SDL_GetError());
 
 		// The mixer is not marked as ready
-		_mixer = new Audio::MixerImpl(desired.freq, true, desired.samples);
+		_mixer = new Audio::MixerImpl(desired.freq, desired.channels >= 2, desired.samples);
 		return;
 	}
 
@@ -88,7 +88,7 @@ void SdlMixerManager::init() {
 			warning("Could not open audio device: %s", SDL_GetError());
 
 			// The mixer is not marked as ready
-			_mixer = new Audio::MixerImpl(desired.freq, true, desired.samples);
+			_mixer = new Audio::MixerImpl(desired.freq, desired.channels >= 2, desired.samples);
 			return;
 		}
 
@@ -103,10 +103,11 @@ void SdlMixerManager::init() {
 	if (_obtained.samples != desired.samples)
 		warning("SDL mixer output buffer size: %d differs from desired: %d", _obtained.samples, desired.samples);
 
-	if (_obtained.channels != 2)
-		error("SDL mixer output requires stereo output device");
+	debug(1, "Output channels: %d", _obtained.channels);
+	if (_obtained.channels != 1 && _obtained.channels != 2)
+		error("SDL mixer output requires mono or stereo output device");
 
-	_mixer = new Audio::MixerImpl(_obtained.freq, true, desired.samples);
+	_mixer = new Audio::MixerImpl(_obtained.freq, _obtained.channels >= 2, desired.samples);
 	assert(_mixer);
 	_mixer->setReady(true);
 
@@ -143,6 +144,12 @@ SDL_AudioSpec SdlMixerManager::getAudioSpec(uint32 outputRate) {
 	if (freq <= 0)
 		freq = outputRate;
 
+	uint32 channels = 2;
+	if (ConfMan.hasKey("output_channels"))
+		channels = ConfMan.getInt("output_channels");
+	if (channels > 2 || channels <= 0)
+		channels = 2;
+
 	// One SDL "sample" is a complete audio frame (i.e. all channels = 1 sample)
 	uint32 samples = 0;
 
@@ -166,7 +173,7 @@ SDL_AudioSpec SdlMixerManager::getAudioSpec(uint32 outputRate) {
 	memset(&desired, 0, sizeof(desired));
 	desired.freq = freq;
 	desired.format = AUDIO_S16SYS;
-	desired.channels = 2;
+	desired.channels = channels;
 	desired.samples = roundDownPowerOfTwo(samples);
 	desired.callback = sdlCallback;
 	desired.userdata = this;

base/commandLine.cpp

@@ -160,6 +160,7 @@ static const char HELP_STRING4[] =
 	"  --dump-midi              Dumps MIDI events to 'dump.mid', until quitting from game\n"
 	"                           (if file already exists, it will be overwritten)\n"
 	"  --enable-gs              Enable Roland GS mode for MIDI playback\n"
+	"  --output-channels=CHANNELS Select output channel count (e.g. 2 for stereo)\n"
 	"  --output-rate=RATE       Select output sample rate in Hz (e.g. 22050)\n"
 	"  --opl-driver=DRIVER      Select AdLib (OPL) emulator (db, mame"
 #ifndef DISABLE_NUKED_OPL
@@ -663,6 +664,9 @@ Common::String parseCommandLine(Common::StringMap &settings, int argc, const cha
 			DO_LONG_COMMAND("list-audio-devices")
 			END_COMMAND
 
+			DO_LONG_OPTION_INT("output-channels")
+			END_OPTION
+
 			DO_LONG_OPTION_INT("output-rate")
 			END_OPTION
 

dists/scummvm.6

@@ -326,6 +326,8 @@ Select AdLib (OPL) emulator
 .Ar nuked ,
 .Ar opl2lpt
 .Pc .
+.It Fl -output-channels= Ns Ar RATE
+Set output channel count (e.g. 2 for stereo).
 .It Fl -output-rate= Ns Ar RATE
 Set output sample rate in Hz (e.g. 22050).
 .It Fl -platform= Ns Ar PLATFORM

doc/docportal/advanced_topics/command_line.rst

@@ -200,6 +200,7 @@ Short options are listed where they are available.
         ``--no-filtering``,,"Forces unfiltered graphics mode"
         ``--no-fullscreen``,``-F``,"Forces windowed mode"
         ``--opl-driver=DRIVER``,,":ref:`Selects AdLib (OPL) emulator <opl>`"
+        ``--output-channels=CHANNELS``,,"Select output channel count"
         ``--output-rate=RATE``,,"Selects output sample rate in Hz"
         ``--path=PATH``,``-p``,"Sets path to where the game is installed"
         ``--platform=STRING``,,":ref:`Specifes platform of game <platform>`. Allowed values: 2gs, 3do, acorn, amiga, atari, c64, fmtowns, nes, mac, pc pc98, pce, segacd, wii, windows."

doc/docportal/advanced_topics/configuration_file.rst

@@ -339,6 +339,11 @@ There are many recognized configuration keys. In the table below, each key is ei
 	- op3lpt
 	- rwopl3 "
 		":ref:`originalsaveload <osl>`",boolean,false,
+		":ref:`output_channels <outputchannels>`",integer,,"
+	Supported values are:
+
+	- 1
+	- 2"
 		":ref:`output_rate <outputrate>`",integer,,"
 	Sensible values are: