Support skipping of multiple frames (so e.g. we can handle 120fps sources).

2 files changed, 12 insertions, 8 deletions

diff --git a/src/lib/frame_rate_change.cc b/src/lib/frame_rate_change.cc
index d4e51d669..6057f9ca3 100644
--- a/src/lib/frame_rate_change.cc
+++ b/src/lib/frame_rate_change.cc
@@ -46,7 +46,7 @@ FrameRateChange::FrameRateChange(double source, int dcp)
 		/* The difference between source and DCP frame rate will be lower
 		   (i.e. better) if we skip.
 		*/
-		_skip = true;
+		_skip = round(source / dcp) - 1;
 	} else if (fabs(_source * 2 - _dcp) < fabs(_source - _dcp)) {
 		/* The difference between source and DCP frame rate would be better
 		   if we repeated each frame once; it may be better still if we
@@ -84,11 +84,13 @@ FrameRateChange::description() const
 {
 	string description;
 
-	if (!_skip && _repeat == 1 && !_change_speed) {
+	if (_skip == 0 && _repeat == 1 && !_change_speed) {
 		description = _("Content and DCP have the same rate.\n");
 	} else {
-		if (_skip) {
+		if (_skip == 1) {
 			description = _("DCP will use every other frame of the content.\n");
+		} else if (_skip >= 2) {
+			description = fmt::format(_("DCP will contain 1 out of every {} frames of the content.\n"), _skip + 1);
 		} else if (_repeat == 2) {
 			description = _("Each content frame will be doubled in the DCP.\n");
 		} else if (_repeat > 2) {
diff --git a/src/lib/frame_rate_change.h b/src/lib/frame_rate_change.h
index 478cadeee..b58e499d8 100644
--- a/src/lib/frame_rate_change.h
+++ b/src/lib/frame_rate_change.h
@@ -43,8 +43,8 @@ public:
 	    to get the effective rate after any skip or repeat has happened.
 	*/
 	double factor() const {
-		if (_skip) {
-			return 0.5;
+		if (_skip > 0) {
+			return 1.0 / (_skip + 1);
 		}
 
 		return _repeat;
@@ -52,7 +52,7 @@ public:
 
 	std::string description() const;
 
-	bool skip() const {
+	int skip() const {
 		return _skip;
 	}
 
@@ -80,8 +80,10 @@ private:
 	double _source = 24;
 	int _dcp = 24;
 
-	/** true to skip every other frame */
-	bool _skip = false;
+	/** Frames to skip between each one to use, e.g.
+	 *  0 to skip no frames, 1 to skip every other one, 2 to skip 2 out of 3, etc.
+	 */
+	int _skip = 0;
 	/** number of times to use each frame (e.g. 1 is normal, 2 means repeat each frame once, and so on) */
 	int _repeat = 1;
 	/** true if this DCP will run its video faster or slower than the source