Adding GetMinTime & GetMinFrame methods to Timeline

src/Timeline.cpp

@@ -472,6 +472,19 @@ int64_t Timeline::GetMaxFrame() {
 	return std::round(max_time * fps);
 }
 
+// Compute the start time of the first timeline clip
+double Timeline::GetMinTime() {
+	// Return cached min_time variable (threadsafe)
+	return min_time;
+}
+
+// Compute the first frame# based on the first clip position
+int64_t Timeline::GetMinFrame() {
+	double fps = info.fps.ToDouble();
+	auto min_time = GetMinTime();
+	return std::round(min_time * fps);
+}
+
 // Apply a FrameMapper to a clip which matches the settings of this timeline
 void Timeline::apply_mapper_to_clip(Clip* clip)
 {
@@ -755,22 +768,52 @@ void Timeline::update_open_clips(Clip *clip, bool does_clip_intersect)
 		"open_clips.size()", open_clips.size());
 }
 
-// Calculate the max duration (in seconds) of the timeline, based on all the clips, and cache the value
+// Calculate the max and min duration (in seconds) of the timeline, based on all the clips, and cache the value
 void Timeline::calculate_max_duration() {
 	double last_clip = 0.0;
 	double last_effect = 0.0;
+	double first_clip = std::numeric_limits<double>::max();
+	double first_effect = std::numeric_limits<double>::max();
 
+	// Find the last and first clip
 	if (!clips.empty()) {
+		// Find the clip with the maximum end frame
 		const auto max_clip = std::max_element(
-				clips.begin(), clips.end(), CompareClipEndFrames());
+			clips.begin(), clips.end(), CompareClipEndFrames());
 		last_clip = (*max_clip)->Position() + (*max_clip)->Duration();
+
+		// Find the clip with the minimum start position (ignoring layer)
+		const auto min_clip = std::min_element(
+			clips.begin(), clips.end(), [](const openshot::Clip* lhs, const openshot::Clip* rhs) {
+				return lhs->Position() < rhs->Position();
+			});
+		first_clip = (*min_clip)->Position();
 	}
+
+	// Find the last and first effect
 	if (!effects.empty()) {
+		// Find the effect with the maximum end frame
 		const auto max_effect = std::max_element(
-				effects.begin(), effects.end(), CompareEffectEndFrames());
+			effects.begin(), effects.end(), CompareEffectEndFrames());
 		last_effect = (*max_effect)->Position() + (*max_effect)->Duration();
+
+		// Find the effect with the minimum start position
+		const auto min_effect = std::min_element(
+			effects.begin(), effects.end(), [](const openshot::EffectBase* lhs, const openshot::EffectBase* rhs) {
+				return lhs->Position() < rhs->Position();
+			});
+		first_effect = (*min_effect)->Position();
 	}
+
+	// Calculate the max and min time
 	max_time = std::max(last_clip, last_effect);
+	min_time = std::min(first_clip, first_effect);
+
+	// If no clips or effects exist, set min_time to 0
+	if (clips.empty() && effects.empty()) {
+		min_time = 0.0;
+		max_time = 0.0;
+	}
 }
 
 // Sort clips by position on the timeline
@@ -1260,6 +1303,10 @@ void Timeline::SetJsonValue(const Json::Value root) {
 	preview_width = info.width;
 	preview_height = info.height;
 
+	// Resort (and recalculate min/max duration)
+	sort_clips();
+	sort_effects();
+
 	// Re-open if needed
 	if (was_open)
 		Open();

src/Timeline.h

@@ -160,7 +160,8 @@ namespace openshot {
 		bool managed_cache; ///< Does this timeline instance manage the cache object
 		std::string path; ///< Optional path of loaded UTF-8 OpenShot JSON project file
 		int max_concurrent_frames; ///< Max concurrent frames to process at one time
-		double max_time; ///> The max duration (in seconds) of the timeline, based on all the clips
+		double max_time; ///> The max duration (in seconds) of the timeline, based on the furthest clip (right edge)
+		double min_time; ///> The min duration (in seconds) of the timeline, based on the position of the first clip (left edge)
 
 		std::map<std::string, std::shared_ptr<openshot::TrackedObjectBase>> tracked_objects; ///< map of TrackedObjectBBoxes and their IDs
 
@@ -286,6 +287,11 @@ namespace openshot {
 		/// Look up the end frame number of the latest element on the timeline
 		int64_t GetMaxFrame();
 
+		/// Look up the position/start time of the first timeline element
+		double GetMinTime();
+		/// Look up the start frame number of the first element on the timeline
+		int64_t GetMinFrame();
+
 		/// Close the timeline reader (and any resources it was consuming)
 		void Close() override;
 

tests/Timeline.cpp

@@ -661,6 +661,67 @@ TEST_CASE( "GetMaxFrame and GetMaxTime", "[libopenshot][timeline]" )
 	CHECK(t.GetMaxTime() == Approx(20.0).margin(0.001));
 }
 
+TEST_CASE( "GetMinFrame and GetMinTime", "[libopenshot][timeline]" )
+{
+    // Create a timeline
+    Timeline t(640, 480, Fraction(30, 1), 44100, 2, LAYOUT_STEREO);
+
+    std::stringstream path1;
+    path1 << TEST_MEDIA_PATH << "interlaced.png";
+    Clip clip1(path1.str());
+    clip1.Id("C1");
+    clip1.Layer(1);
+    clip1.Position(50); // Start at 50 seconds
+    clip1.End(45);      // Ends at 95 seconds
+    t.AddClip(&clip1);
+
+    CHECK(t.GetMinTime() == Approx(50.0).margin(0.001));
+    CHECK(t.GetMinFrame() == 50 * 30);
+
+    Clip clip2(path1.str());
+    clip2.Id("C2");
+    clip2.Layer(2);
+    clip2.Position(0);  // Start at 0 seconds
+    clip2.End(55);      // Ends at 55 seconds
+    t.AddClip(&clip2);
+
+    CHECK(t.GetMinTime() == Approx(0.0).margin(0.001));
+    CHECK(t.GetMinFrame() == 0);
+
+    clip1.Position(80); // Move clip1 to start at 80 seconds
+    clip2.Position(100); // Move clip2 to start at 100 seconds
+    CHECK(t.GetMinTime() == Approx(80.0).margin(0.001));
+    CHECK(t.GetMinFrame() == 80 * 30);
+
+    clip2.Position(20); // Adjust clip2 to start at 20 seconds
+    CHECK(t.GetMinTime() == Approx(20.0).margin(0.001));
+    CHECK(t.GetMinFrame() == 20 * 30);
+
+    clip2.End(35); // Adjust clip2 to end at 35 seconds
+    CHECK(t.GetMinTime() == Approx(20.0).margin(0.001));
+    CHECK(t.GetMinFrame() == 20 * 30);
+
+    t.RemoveClip(&clip1);
+    CHECK(t.GetMinTime() == Approx(20.0).margin(0.001));
+    CHECK(t.GetMinFrame() == 20 * 30);
+
+    // Update Clip's basic properties with JSON Diff
+    std::stringstream json_change1;
+    json_change1 << "[{\"type\":\"update\",\"key\":[\"clips\",{\"id\":\"C2\"}],\"value\":{\"id\":\"C2\",\"layer\":4000000,\"position\":5.0,\"start\":0,\"end\":10},\"partial\":false}]";
+    t.ApplyJsonDiff(json_change1.str());
+
+    CHECK(t.GetMinTime() == Approx(5.0).margin(0.001));
+    CHECK(t.GetMinFrame() == 5 * 30);
+
+    // Insert NEW Clip with JSON Diff
+    std::stringstream json_change2;
+    json_change2 << "[{\"type\":\"insert\",\"key\":[\"clips\"],\"value\":{\"id\":\"C3\",\"layer\":4000000,\"position\":10.0,\"start\":0,\"end\":10,\"reader\":{\"acodec\":\"\",\"audio_bit_rate\":0,\"audio_stream_index\":-1,\"audio_timebase\":{\"den\":1,\"num\":1},\"channel_layout\":4,\"channels\":0,\"display_ratio\":{\"den\":1,\"num\":1},\"duration\":3600.0,\"file_size\":\"160000\",\"fps\":{\"den\":1,\"num\":30},\"has_audio\":false,\"has_single_image\":true,\"has_video\":true,\"height\":200,\"interlaced_frame\":false,\"metadata\":{},\"path\":\"" << path1.str() << "\",\"pixel_format\":-1,\"pixel_ratio\":{\"den\":1,\"num\":1},\"sample_rate\":0,\"top_field_first\":true,\"type\":\"QtImageReader\",\"vcodec\":\"\",\"video_bit_rate\":0,\"video_length\":\"108000\",\"video_stream_index\":-1,\"video_timebase\":{\"den\":30,\"num\":1},\"width\":200}},\"partial\":false}]";
+    t.ApplyJsonDiff(json_change2.str());
+
+    CHECK(t.GetMinTime() == Approx(5.0).margin(0.001));
+    CHECK(t.GetMinFrame() == 5 * 30);
+}
+
 TEST_CASE( "Multi-threaded Timeline GetFrame", "[libopenshot][timeline]" )
 {
 	Timeline *t = new Timeline(1280, 720, Fraction(24, 1), 48000, 2, LAYOUT_STEREO);