Fix overlapping burnt-in subtitles in some cases (#959).

Firstly, when finding subtitles that exist during a period, only
return those which overlap more than half the period.  This means
that, in a fight over a frame, the longest-running subtitle in that
frame will win.

Secondly, make SubtitleDecoder::get pick the wanted subtitles from
the cache simply by comparing their periods to those that were
requested.  I think this is nicer than what was there before
(basically reevaulating 'what subtitle(s) for this period') and
also makes the first part of this commit effective.

1 files changed, 4 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 34fe178a4..d603234d0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2016-10-08  Carl Hetherington  <cth@carlh.net>
+
+	* Fix overlapping burnt-in subtitles in some cases (#959).
+
 2016-10-07  Carl Hetherington  <cth@carlh.net>
 
 	* Fix XML subtitle output in some cases.