obs-transition: Add crossfade option to stinger

Add option in properties that let you choose how audio is mixed during
transition:
- Fade Out/Fade In (existing behavior, default)
- Crossfade

Closes jp9000/obs-studio#1028

plugins/obs-transitions/data/locale/en-US.ini

@@ -17,6 +17,9 @@ TransitionPointFrame="Transition Point (frame)"
 TransitionPointType="Transition Point Type"
 TransitionPointTypeFrame="Frame"
 TransitionPointTypeTime="Time (milliseconds)"
+AudioFadeStyle="Audio Fade Style"
+AudioFadeStyle.FadeOutFadeIn="Fade out to transition point then fade in"
+AudioFadeStyle.CrossFade="Crossfade"
 SwitchPoint="Peak Color Point (percentage)"
 LumaWipeTransition="Luma Wipe"
 LumaWipe.Image="Image"

plugins/obs-transitions/transition-stinger.c

@@ -3,6 +3,11 @@
 #define TIMING_TIME  0
 #define TIMING_FRAME 1
 
+enum fade_style {
+	FADE_STYLE_FADE_OUT_FADE_IN,
+	FADE_STYLE_CROSS_FADE
+};
+
 struct stinger_info {
 	obs_source_t *source;
 
@@ -18,6 +23,10 @@ struct stinger_info {
 	bool transitioning;
 	bool transition_point_is_frame;
 	int monitoring_type;
+	enum fade_style fade_style;
+
+	float (*mix_a)(void *data, float t);
+	float (*mix_b)(void *data, float t);
 };
 
 static const char *stinger_get_name(void *type_data)
@@ -26,6 +35,11 @@ static const char *stinger_get_name(void *type_data)
 	return obs_module_text("StingerTransition");
 }
 
+static float mix_a_fade_in_out(void *data, float t);
+static float mix_b_fade_in_out(void *data, float t);
+static float mix_a_cross_fade(void *data, float t);
+static float mix_b_cross_fade(void *data, float t);
+
 static void stinger_update(void *data, obs_data_t *settings)
 {
 	struct stinger_info *s = data;
@@ -51,6 +65,21 @@ static void stinger_update(void *data, obs_data_t *settings)
 
 	s->monitoring_type = obs_data_get_int(settings,"audio_monitoring");
 	obs_source_set_monitoring_type(s->media_source, s->monitoring_type);
+
+	s->fade_style = (enum fade_style)obs_data_get_int(settings,
+			"audio_fade_style");
+
+	switch (s->fade_style) {
+	default:
+	case FADE_STYLE_FADE_OUT_FADE_IN:
+		s->mix_a = mix_a_fade_in_out;
+		s->mix_b = mix_b_fade_in_out;
+		break;
+	case FADE_STYLE_CROSS_FADE:
+		s->mix_a = mix_a_cross_fade;
+		s->mix_b = mix_b_cross_fade;
+		break;
+	}
 }
 
 static void *stinger_create(obs_data_t *settings, obs_source_t *source)
@@ -58,6 +87,8 @@ static void *stinger_create(obs_data_t *settings, obs_source_t *source)
 	struct stinger_info *s = bzalloc(sizeof(*s));
 
 	s->source = source;
+	s->mix_a = mix_a_fade_in_out;
+	s->mix_b = mix_b_fade_in_out;
 
 	obs_transition_enable_fixed(s->source, true, 0);
 	obs_source_update(source, settings);
@@ -112,18 +143,30 @@ static inline float calc_fade(float t, float mul)
 	return t > 1.0f ? 1.0f : t;
 }
 
-static float mix_a(void *data, float t)
+static float mix_a_fade_in_out(void *data, float t)
 {
 	struct stinger_info *s = data;
 	return 1.0f - calc_fade(t, s->transition_a_mul);
 }
 
-static float mix_b(void *data, float t)
+static float mix_b_fade_in_out(void *data, float t)
 {
 	struct stinger_info *s = data;
 	return 1.0f - calc_fade(1.0f - t, s->transition_b_mul);
 }
 
+static float mix_a_cross_fade(void *data, float t)
+{
+	UNUSED_PARAMETER(data);
+	return 1.0f - t;
+}
+
+static float mix_b_cross_fade(void *data, float t)
+{
+	UNUSED_PARAMETER(data);
+	return t;
+}
+
 static bool stinger_audio_render(void *data, uint64_t *ts_out,
 		struct obs_source_audio_mix *audio, uint32_t mixers,
 		size_t channels, size_t sample_rate)
@@ -138,7 +181,7 @@ static bool stinger_audio_render(void *data, uint64_t *ts_out,
 	}
 
 	bool success = obs_transition_audio_render(s->source, ts_out,
-		audio, mixers, channels, sample_rate, mix_a, mix_b);
+		audio, mixers, channels, sample_rate, s->mix_a, s->mix_b);
 	if (!ts)
 		return success;
 
@@ -296,6 +339,16 @@ static obs_properties_t *stinger_properties(void *data)
 			obs_module_text("AudioMonitoring.Both"),
 			OBS_MONITORING_TYPE_MONITOR_AND_OUTPUT);
 
+	obs_property_t *audio_fade_style = obs_properties_add_list(ppts,
+			"audio_fade_style", obs_module_text("AudioFadeStyle"),
+			OBS_COMBO_TYPE_LIST, OBS_COMBO_FORMAT_INT);
+	obs_property_list_add_int(audio_fade_style,
+			obs_module_text("AudioFadeStyle.FadeOutFadeIn"),
+			FADE_STYLE_FADE_OUT_FADE_IN);
+	obs_property_list_add_int(audio_fade_style,
+			obs_module_text("AudioFadeStyle.CrossFade"),
+			FADE_STYLE_CROSS_FADE);
+
 	UNUSED_PARAMETER(data);
 	return ppts;
 }