Add scene detection threshold

Cycle.cpp

@@ -20,6 +20,8 @@
 #include <memory>
 #include "Cycle.h"
 
+float sceneThreshold;
+
 int cmpDescendingDiff(const void * a, const void * b);
 
 Cycle::Cycle(int length, int creates) :
@@ -75,22 +77,44 @@ bool Cycle::includes(int frame) {
 }
 
 bool Cycle::isBadFrame(int frame) {
-	for (int i = 0; i < creates; i++) {
+	// Rules:
+	// 1. A scene frame is only considered if there is at least two frames in the cycle.
+	// 2. If there are two or more frames, and at least one in the cycle is above the threshold,
+	//    then that frame will be regarded as the scene change, and all others will be judged
+	//    depending on number of creates required for the cycle (ordered by diffs in descending order).
+	sortDiffsIfNeeded();
+	int sceneChanges = 0;
+	for (int i = 0; i < creates + sceneChanges && i < length; i++) {
+		if (creates < length && sceneChanges < 1 && sceneThreshold < sortedDiffs[i].diff) {
+			sceneChanges++;
+			continue;
+		}
 		if (getFrameWithLargestDiff(i) == frame) {
 			return true;
 		}
 	}
 	return false;
 }
 
+bool Cycle::isSceneChange(int frame) {
+	sortDiffsIfNeeded();
+	return creates < length // Ignore scene change logic unless there is an *option* to select frames.
+		&& sortedDiffs[0].frame == frame
+		&& sceneThreshold < sortedDiffs[0].diff;
+}
+
 int Cycle::getFrameWithLargestDiff(int offset) {
+	sortDiffsIfNeeded();
+	if (offset > length - 1) return -1;
+	return sortedDiffs[offset].frame;
+}
+
+void Cycle::sortDiffsIfNeeded() {
 	if (!sorted) {
 		memcpy(sortedDiffs.get(), diffs.get(), length * sizeof(CycleDiff));
 		qsort(sortedDiffs.get(), length, sizeof(CycleDiff), cmpDescendingDiff);
 		sorted = true;
 	}
-	if (offset > length - 1) return -1;
-	return sortedDiffs[offset].frame;
 }
 
 int cmpDescendingDiff(const void * a, const void * b) {

Cycle.h

@@ -20,6 +20,8 @@
 
 #include <memory>
 
+extern float sceneThreshold;
+
 typedef struct {
 	int frame;      // frame number
 	float diff;     // frame diff to previous
@@ -33,6 +35,7 @@ typedef struct {
 
 class Cycle {
 	bool sorted;
+	void sortDiffsIfNeeded();
 
 public:
 	int creates;        // number of frames to create in the cycle  (n in m creation)
@@ -47,6 +50,7 @@ class Cycle {
 	int getFrameWithLargestDiff(int offset);
 	bool includes(int frame);
 	bool isBadFrame(int n);
+	bool isSceneChange(int n);
 	void reset();
 	void updateFrameMap();
 };

Readme.md

@@ -26,6 +26,9 @@ Default: `1`
 When scripting AviSynth, users are prevented from accessing individual frames, as selecting frames is the purview of the application leveraging AviSynth. Filter plugins however have greater flexibility and can pick and choose which frame to use and this *offset* option gives you some flexibility in selecting replacement frames that do not necessarily reside at the same frame number as the primary clip's. Of course, you could achieve the effect of fixed offset like this by using *Trim* and *Loop*, so this is just a shorthand to save you from having to stitch and slice clips in the script.  
 Default: `-1` (frame with number before current_frame)
 
+* `scene`: Scene detection threshold.  
+Any frame difference ("YDifferenceFromPrevious") above this threshold will be regarded as a scene change. When a scene change frame is detected, the frame from the source clip will be used instead of the alt-clip. When a scene change frame is detected in a cycle, the frame with the next largest frame diff will be picked instead. In short, if a scene change is detected in a cycle, then the frame with the largest diff will be removed from skip tagging. There is _one_ exception to this rule, namely that the number of frames to "create" must be less than the "cycle" length. If both are equal, then scene detection is disabled, so as to ensure the specified number of frames to create per cycle is always followed. The exception is there to ensure audio does not get out of sync, as the number of frames inserted would otherwise be totally dependent on how many scene changes were detected in a given clip.
+
 * `debug`: Display various internal metrics as an image overlay.  
 Default: `false`
 

SmoothSkip.cpp

@@ -21,6 +21,7 @@
 #include <stdio.h>
 #include "SmoothSkip.h"
 #include "CycleCache.h"
+#include "Cycle.h"
 #include "FrameDiff.h"
 #include "3rd-party/info.h"
 
@@ -75,11 +76,13 @@ PVideoFrame __stdcall SmoothSkip::GetFrame(int n, IScriptEnvironment* env) {
 		frame = info(env, frame, msg, 0, row++);
 		sprintf(msg, "FPS:   %.3f (child: %.3f)", GetFps(this), GetFps(child));
 		frame = info(env, frame, msg, 0, row++);
+		sprintf(msg, "Scene: %.1f", sceneThreshold);
+		frame = info(env, frame, msg, 0, row++);
 		sprintf(msg, "Cycle frame diffs (child):");
 		frame = info(env, frame, msg, 0, row++);
 		for (int i = 0; i < cycle.length; i++) {
 			sprintf(msg, "%s %d (%.5f) ",
-				cycle.isBadFrame(cycle.diffs[i].frame) ? "*" : " ",
+				cycle.isSceneChange(cycle.diffs[i].frame) ? "S" : cycle.isBadFrame(cycle.diffs[i].frame) ? "*" : " ",
 				cycle.diffs[i].frame,
 				cycle.diffs[i].diff);
 			frame = info(env, frame, msg, 0, row++);
@@ -109,7 +112,7 @@ void SmoothSkip::updateCycle(IScriptEnvironment* env, int cn, VideoInfo cvi, Cyc
 
 // Constructor
 SmoothSkip::SmoothSkip(PClip _child, PClip _altclip, int cycleLen, int creates, int _offset, 
-	                   bool _debug, IScriptEnvironment* env) :
+	                   double sceneThresh, bool _debug, IScriptEnvironment* env) :
 GenericVideoFilter(_child), altclip(_altclip), offset(_offset), debug(_debug) {
 	VideoInfo avi = altclip->GetVideoInfo();
 	VideoInfo cvi = child->GetVideoInfo();
@@ -120,6 +123,9 @@ GenericVideoFilter(_child), altclip(_altclip), offset(_offset), debug(_debug) {
 	if (cycleLen > cvi.num_frames) raiseError(env, "Cycle can't be larger than the frames in source clip");
 	if (cycleLen > avi.num_frames) raiseError(env, "Cycle can't be larger than the frames in alt clip");
 	if (creates < 1 || creates > cycleLen) raiseError(env, "Create must be between 1 and the value of cycle (1 <= create <= cycle)");
+	if (sceneThresh < 0) raiseError(env, "Scene threshold must be >= 0.0");
+
+	sceneThreshold = static_cast<float>(sceneThresh); // Assign to static variable in the cycle header, so it can be used in the cycle logic
 
 	try {
 		cycles = new CycleCache(cycleLen, creates, cvi.num_frames);
@@ -146,7 +152,8 @@ AVSValue __cdecl Create_SmoothSkip(AVSValue args, void* user_data, IScriptEnviro
 		args[2].AsInt(4),      // cycle
 		args[3].AsInt(1),      // create
 		args[4].AsInt(0),      // offset
-		args[5].AsBool(false), // debug
+		args[5].AsFloat(32),   // offset
+		args[6].AsBool(false), // debug
 		env);
 }
 
@@ -188,7 +195,7 @@ FrameMap SmoothSkip::getFrameMapping(IScriptEnvironment* env, int n) {
 
 	FrameMap map = cycle.frameMap[cycleOffset];
 	if (map.dstframe != n)
-		raiseError(env, "Frame counting is out of whack");
+		raiseError(env, "BUG! Frame counting is out of whack. Please report this to the author.");
 
 	return map;
 }

SmoothSkip.h

@@ -26,14 +26,14 @@
 #define VERSION "1.0.3"
 
 class SmoothSkip : public GenericVideoFilter {
-	PClip altclip;   // The super clip from MVTools2 
-	bool debug;      // debug arg
-	int offset;      // frame offset used to get frame from the alternate clip.
+	PClip altclip;     // The super clip from MVTools2
+	bool debug;        // debug arg
+	int offset;        // frame offset used to get frame from the alternate clip.
 
 public:
 	CycleCache* cycles;
 	SmoothSkip(PClip _child, PClip _altclip, int cycleLen, int creates, int offset, 
-		       bool _debug, IScriptEnvironment* env);
+			   double sceneThreshold, bool _debug, IScriptEnvironment* env);
 	~SmoothSkip();
 	PVideoFrame __stdcall GetFrame(int n, IScriptEnvironment* env);
 private:
@@ -46,7 +46,7 @@ class SmoothSkip : public GenericVideoFilter {
 AVSValue __cdecl Create_SmoothSkip(AVSValue args, void* user_data, IScriptEnvironment* env);
 
 extern "C" __declspec(dllexport) const char* __stdcall AvisynthPluginInit2(IScriptEnvironment* env) {
-	env->AddFunction("SmoothSkip", "cc[CYCLE]i[CREATE]i[OFFSET]i[DEBUG]b", Create_SmoothSkip, 0);
+	env->AddFunction("SmoothSkip", "cc[CYCLE]i[CREATE]i[OFFSET]f[SCENE]i[DEBUG]b", Create_SmoothSkip, 0);
 	return "'SmoothSkip' plugin v" VERSION ", author: tinjon[at]gmail.com";
 }