Adding new audio mixing enum, to allow for no automatic audio mixing, average mixing (where all overlapping clips average to 100% audio), or reduce mixing (where clips overlapping clips are all reduced by a constant value to reduce popping). (#131)

include/Clip.h

@@ -155,6 +155,7 @@ namespace openshot {
 		ScaleType scale; ///< The scale determines how a clip should be resized to fit it's parent
 		AnchorType anchor; ///< The anchor determines what parent a clip should snap to
         FrameDisplayType display; ///< The format to display the frame number (if any)
+		VolumeMixType mixing; ///< What strategy should be followed when mixing audio with other clips
 
 		/// Default Constructor
 		Clip();

include/Enums.h

@@ -69,5 +69,13 @@ namespace openshot
 		FRAME_DISPLAY_TIMELINE, ///< Display the timeline's frame number
 		FRAME_DISPLAY_BOTH      ///< Display both the clip's and timeline's frame number
 	};
+
+	/// This enumeration determines the strategy when mixing audio with other clips.
+	enum VolumeMixType
+	{
+		VOLUME_MIX_NONE,   	///< Do not apply any volume mixing adjustments. Just add the samples together.
+		VOLUME_MIX_AVERAGE,	///< Evenly divide the overlapping clips volume keyframes, so that the sum does not exceed 100%
+		VOLUME_MIX_REDUCE 	///< Reduce volume by about %25, and then mix (louder, but could cause pops if the sum exceeds 100%)
+	};
 }
 #endif

src/Clip.cpp

@@ -41,6 +41,7 @@ void Clip::init_settings()
 	scale = SCALE_FIT;
 	anchor = ANCHOR_CANVAS;
 	display = FRAME_DISPLAY_NONE;
+	mixing = VOLUME_MIX_NONE;
 	waveform = false;
 	previous_properties = "";
 
@@ -694,6 +695,7 @@ string Clip::PropertiesJSON(int64_t requested_frame) {
 	root["gravity"] = add_property_json("Gravity", gravity, "int", "", NULL, 0, 8, false, requested_frame);
 	root["scale"] = add_property_json("Scale", scale, "int", "", NULL, 0, 3, false, requested_frame);
 	root["display"] = add_property_json("Frame Number", display, "int", "", NULL, 0, 3, false, requested_frame);
+	root["mixing"] = add_property_json("Volume Mixing", mixing, "int", "", NULL, 0, 2, false, requested_frame);
 	root["waveform"] = add_property_json("Waveform", waveform, "int", "", NULL, 0, 1, false, requested_frame);
 
 	// Add gravity choices (dropdown style)
@@ -719,6 +721,11 @@ string Clip::PropertiesJSON(int64_t requested_frame) {
 	root["display"]["choices"].append(add_property_choice_json("Timeline", FRAME_DISPLAY_TIMELINE, display));
 	root["display"]["choices"].append(add_property_choice_json("Both", FRAME_DISPLAY_BOTH, display));
 
+	// Add volume mixing choices (dropdown style)
+	root["mixing"]["choices"].append(add_property_choice_json("None", VOLUME_MIX_NONE, mixing));
+	root["mixing"]["choices"].append(add_property_choice_json("Average", VOLUME_MIX_AVERAGE, mixing));
+	root["mixing"]["choices"].append(add_property_choice_json("Reduce", VOLUME_MIX_REDUCE, mixing));
+
 	// Add waveform choices (dropdown style)
 	root["waveform"]["choices"].append(add_property_choice_json("Yes", true, waveform));
 	root["waveform"]["choices"].append(add_property_choice_json("No", false, waveform));
@@ -758,6 +765,7 @@ Json::Value Clip::JsonValue() {
 	root["scale"] = scale;
 	root["anchor"] = anchor;
 	root["display"] = display;
+	root["mixing"] = mixing;
 	root["waveform"] = waveform;
 	root["scale_x"] = scale_x.JsonValue();
 	root["scale_y"] = scale_y.JsonValue();
@@ -844,6 +852,8 @@ void Clip::SetJsonValue(Json::Value root) {
 		anchor = (AnchorType) root["anchor"].asInt();
 	if (!root["display"].isNull())
 		display = (FrameDisplayType) root["display"].asInt();
+	if (!root["mixing"].isNull())
+		mixing = (VolumeMixType) root["mixing"].asInt();
 	if (!root["waveform"].isNull())
 		waveform = root["waveform"].asBool();
 	if (!root["scale_x"].isNull())

src/Timeline.cpp

@@ -294,11 +294,24 @@ void Timeline::add_layer(std::shared_ptr<Frame> new_frame, Clip* source_clip, in
 		if (source_frame->GetAudioChannelsCount() == info.channels && source_clip->has_audio.GetInt(clip_frame_number) != 0)
 			for (int channel = 0; channel < source_frame->GetAudioChannelsCount(); channel++)
 			{
-				float previous_volume = source_clip->volume.GetValue(clip_frame_number - 1) / fmaxf(max_volume, 1.0); // previous frame's percentage of volume (0 to 1)
+				// Get volume from previous frame and this frame
-				float volume = source_clip->volume.GetValue(clip_frame_number) / fmaxf(max_volume, 1.0); // percentage of volume (0 to 1)
+				float previous_volume = source_clip->volume.GetValue(clip_frame_number - 1);
+				float volume = source_clip->volume.GetValue(clip_frame_number);
 				int channel_filter = source_clip->channel_filter.GetInt(clip_frame_number); // optional channel to filter (if not -1)
 				int channel_mapping = source_clip->channel_mapping.GetInt(clip_frame_number); // optional channel to map this channel to (if not -1)
 
+				// Apply volume mixing strategy
+				if (source_clip->mixing == VOLUME_MIX_AVERAGE && max_volume > 1.0) {
+					// Don't allow this clip to exceed 100% (divide volume equally between all overlapping clips with volume
+					previous_volume = previous_volume / max_volume;
+					volume = volume / max_volume;
+				}
+				else if (source_clip->mixing == VOLUME_MIX_REDUCE && max_volume > 1.0) {
+					// Reduce clip volume by a bit, hoping it will prevent exceeding 100% (but it is very possible it will)
+					previous_volume = previous_volume * 0.77;
+					volume = volume * 0.77;
+				}
+
 				// If channel filter enabled, check for correct channel (and skip non-matching channels)
 				if (channel_filter != -1 && channel_filter != channel)
 					continue; // skip to next channel
@@ -760,14 +773,18 @@ std::shared_ptr<Frame> Timeline::GetFrame(int64_t requested_frame)
 							long nearby_clip_start_frame = (nearby_clip->Start() * info.fps.ToDouble()) + 1;
 							long nearby_clip_frame_number = frame_number - nearby_clip_start_position + nearby_clip_start_frame;
 
+							// Determine if top clip
 							if (clip->Id() != nearby_clip->Id() && clip->Layer() == nearby_clip->Layer() &&
                                     nearby_clip_start_position <= frame_number && nearby_clip_end_position >= frame_number &&
                                     nearby_clip_start_position > clip_start_position && is_top_clip == true) {
 								is_top_clip = false;
 							}
 
-							if (nearby_clip_start_position <= frame_number && nearby_clip_end_position >= frame_number) {
+							// Determine max volume of overlapping clips
-								max_volume += nearby_clip->volume.GetValue(nearby_clip_frame_number);
+							if (nearby_clip->Reader() && nearby_clip->Reader()->info.has_audio &&
+									nearby_clip->has_audio.GetInt(nearby_clip_frame_number) != 0 &&
+									nearby_clip_start_position <= frame_number && nearby_clip_end_position >= frame_number) {
+									max_volume += nearby_clip->volume.GetValue(nearby_clip_frame_number);
 							}
 						}