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

[dcpomatic.git] / src / lib / frame_rate_change.cc

diff --git a/src/lib/frame_rate_change.cc b/src/lib/frame_rate_change.cc
new file mode 100644 (file)
index 0000000..3e9c4b5
--- /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);
+               }
+       }
+}