UI: Implement stereo balancing

libobs/obs-internal.h

@@ -608,6 +608,7 @@ struct obs_source {
 	float                           volume;
 	int64_t                         sync_offset;
 	int64_t                         last_sync_offset;
+	float                           balance;
 
 	/* async video data */
 	gs_texture_t                    *async_texture;

libobs/obs-source.c

@@ -16,6 +16,7 @@
 ******************************************************************************/
 
 #include <inttypes.h>
+#include <math.h>
 
 #include "media-io/format-conversion.h"
 #include "media-io/video-frame.h"
@@ -140,6 +141,7 @@ bool obs_source_init(struct obs_source *source)
 	source->user_volume = 1.0f;
 	source->volume = 1.0f;
 	source->sync_offset = 0;
+	source->balance = 0.5f;
 	pthread_mutex_init_value(&source->filter_mutex);
 	pthread_mutex_init_value(&source->async_mutex);
 	pthread_mutex_init_value(&source->audio_mutex);
@@ -2589,6 +2591,37 @@ static void downmix_to_mono_planar(struct obs_source *source, uint32_t frames)
 	}
 }
 
+static void process_audio_balancing(struct obs_source *source, uint32_t frames,
+		float balance, enum obs_balance_type type)
+{
+	float **data = (float**)source->audio_data.data;
+
+	switch(type) {
+	case OBS_BALANCE_TYPE_SINE_LAW:
+		for (uint32_t frame = 0; frame < frames; frame++) {
+			data[0][frame] = data[0][frame] *
+				sinf((1.0f - balance) * (M_PI/2.0f));
+			data[1][frame] = data[1][frame] *
+				sinf(balance * (M_PI/2.0f));
+		}
+		break;
+	case OBS_BALANCE_TYPE_SQUARE_LAW:
+		for (uint32_t frame = 0; frame < frames; frame++) {
+			data[0][frame] = data[0][frame] * sqrtf(1.0f - balance);
+			data[1][frame] = data[1][frame] * sqrtf(balance);
+		}
+		break;
+	case OBS_BALANCE_TYPE_LINEAR:
+		for (uint32_t frame = 0; frame < frames; frame++) {
+			data[0][frame] = data[0][frame] * (1.0f - balance);
+			data[1][frame] = data[1][frame] * balance;
+		}
+		break;
+	default:
+		break;
+	}
+}
+
 /* resamples/remixes new audio to the designated main audio output format */
 static void process_audio(obs_source_t *source,
 		const struct obs_source_audio *audio)
@@ -2622,6 +2655,13 @@ static void process_audio(obs_source_t *source,
 
 	mono_output = audio_output_get_channels(obs->audio.audio) == 1;
 
+	if ((!mono_output && source->sample_info.speakers == SPEAKERS_STEREO) ||
+			!(source->balance <= 0.51f &&
+			  source->balance >= 0.49f)) {
+		process_audio_balancing(source, frames, source->balance,
+				OBS_BALANCE_TYPE_SINE_LAW);
+	}
+
 	if (!mono_output && (source->flags & OBS_SOURCE_FLAG_FORCE_MONO) != 0)
 		downmix_to_mono_planar(source, frames);
 }
@@ -4165,3 +4205,25 @@ EXPORT void obs_enable_source_type(const char *name, bool enable)
 	else
 		info->output_flags |= OBS_SOURCE_CAP_DISABLED;
 }
+
+enum speaker_layout obs_source_get_speaker_layout(obs_source_t *source)
+{
+	if (!obs_source_valid(source, "obs_source_get_audio_channels"))
+		return SPEAKERS_UNKNOWN;
+
+	return source->sample_info.speakers;
+}
+
+void obs_source_set_balance_value(obs_source_t *source, float balance)
+{
+	if (!obs_source_valid(source, "obs_source_set_balance_value"))
+		return;
+
+	source->balance = balance;
+}
+
+float obs_source_get_balance_value(const obs_source_t *source)
+{
+	return obs_source_valid(source, "obs_source_get_balance_value") ?
+		source->balance : 0.5f;
+}

libobs/obs-source.h

@@ -38,6 +38,11 @@ enum obs_source_type {
 	OBS_SOURCE_TYPE_SCENE,
 };
 
+enum obs_balance_type {
+	OBS_BALANCE_TYPE_SINE_LAW,
+	OBS_BALANCE_TYPE_SQUARE_LAW,
+	OBS_BALANCE_TYPE_LINEAR,
+};
 
 /**
  * @name Source output flags

libobs/obs.c

@@ -1563,6 +1563,7 @@ static obs_source_t *obs_load_source_type(obs_data_t *source_data)
 	obs_data_t   *settings = obs_data_get_obj(source_data, "settings");
 	obs_data_t   *hotkeys  = obs_data_get_obj(source_data, "hotkeys");
 	double       volume;
+	double       balance;
 	int64_t      sync;
 	uint32_t     flags;
 	uint32_t     mixers;
@@ -1578,6 +1579,10 @@ static obs_source_t *obs_load_source_type(obs_data_t *source_data)
 	volume = obs_data_get_double(source_data, "volume");
 	obs_source_set_volume(source, (float)volume);
 
+	obs_data_set_default_double(source_data, "balance", 0.5);
+	balance = obs_data_get_double(source_data, "balance");
+	obs_source_set_balance_value(source, (float)balance);
+
 	sync = obs_data_get_int(source_data, "sync");
 	obs_source_set_sync_offset(source, sync);
 
@@ -1716,6 +1721,7 @@ obs_data_t *obs_save_source(obs_source_t *source)
 	obs_data_t *hotkey_data = source->context.hotkey_data;
 	obs_data_t *hotkeys;
 	float      volume      = obs_source_get_volume(source);
+	float      balance     = obs_source_get_balance_value(source);
 	uint32_t   mixers      = obs_source_get_audio_mixers(source);
 	int64_t    sync        = obs_source_get_sync_offset(source);
 	uint32_t   flags       = obs_source_get_flags(source);
@@ -1748,6 +1754,7 @@ obs_data_t *obs_save_source(obs_source_t *source)
 	obs_data_set_int   (source_data, "sync",     sync);
 	obs_data_set_int   (source_data, "flags",    flags);
 	obs_data_set_double(source_data, "volume",   volume);
+	obs_data_set_double(source_data, "balance",  balance);
 	obs_data_set_bool  (source_data, "enabled",  enabled);
 	obs_data_set_bool  (source_data, "muted",    muted);
 	obs_data_set_bool  (source_data, "push-to-mute", push_to_mute);

libobs/obs.h

@@ -893,6 +893,15 @@ EXPORT void obs_source_set_volume(obs_source_t *source, float volume);
 /** Gets the user volume for a source that has audio output */
 EXPORT float obs_source_get_volume(const obs_source_t *source);
 
+/* Gets speaker layout of a source */
+EXPORT enum speaker_layout obs_source_get_speaker_layout(obs_source_t *source);
+
+/** Sets the balance value for a stereo audio source */
+EXPORT void obs_source_set_balance_value(obs_source_t *source, float balance);
+
+/** Gets the balance value for a stereo audio source */
+EXPORT float obs_source_get_balance_value(const obs_source_t *source);
+
 /** Sets the audio sync offset (in nanoseconds) for a source */
 EXPORT void obs_source_set_sync_offset(obs_source_t *source, int64_t offset);