Back-port v2's rename and slight extension of FrameRateConversion.

1 files changed, 91 insertions, 0 deletions

diff --git a/src/lib/frame_rate_change.cc b/src/lib/frame_rate_change.cc
new file mode 100644
index 000000000..3e9c4b505
--- /dev/null
+++ b/src/lib/frame_rate_change.cc
@@ -0,0 +1,91 @@
+/*
+    Copyright (C) 2012-2014 Carl Hetherington <cth@carlh.net>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+*/
+
+#include <cmath>
+#include "frame_rate_change.h"
+#include "compose.hpp"
+
+#include "i18n.h"
+
+static bool
+about_equal (float a, float b)
+{
+	/* A film of F seconds at f FPS will be Ff frames;
+	   Consider some delta FPS d, so if we run the same
+	   film at (f + d) FPS it will last F(f + d) seconds.
+
+	   Hence the difference in length over the length of the film will
+	   be F(f + d) - Ff frames
+	    = Ff + Fd - Ff frames
+	    = Fd frames
+	    = Fd/f seconds
+ 
+	   So if we accept a difference of 1 frame, ie 1/f seconds, we can
+	   say that
+
+	   1/f = Fd/f
+	ie 1 = Fd
+	ie d = 1/F
+ 
+	   So for a 3hr film, ie F = 3 * 60 * 60 = 10800, the acceptable
+	   FPS error is 1/F ~= 0.0001 ~= 10-e4
+	*/
+
+	return (fabs (a - b) < 1e-4);
+}
+
+
+FrameRateChange::FrameRateChange (float source, int dcp)
+	: skip (false)
+	, repeat (1)
+	, change_speed (false)
+{
+	if (fabs (source / 2.0 - dcp) < fabs (source - dcp)) {
+		/* The difference between source and DCP frame rate will be lower
+		   (i.e. better) if we skip.
+		*/
+		skip = true;
+	} 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
+		   repeated more than once.  Work out the required repeat.
+		*/
+		repeat = round (dcp / source);
+	}
+
+	speed_up = dcp / (source * factor());
+	change_speed = !about_equal (speed_up, 1.0);
+
+	if (!skip && repeat == 1 && !change_speed) {
+		description = _("Content and DCP have the same rate.\n");
+	} else {
+		if (skip) {
+			description = _("DCP will use every other frame of the content.\n");
+		} else if (repeat == 2) {
+			description = _("Each content frame will be doubled in the DCP.\n");
+		} else if (repeat > 2) {
+			description = String::compose (_("Each content frame will be repeated %1 more times in the DCP.\n"), repeat - 1);
+		}
+
+		if (change_speed) {
+			float const pc = dcp * 100 / (source * factor());
+			description += String::compose (_("DCP will run at %1%% of the content speed.\n"), pc);
+		}
+	}
+}