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/src/lib/dcpomatic_time.h b/src/lib/dcpomatic_time.h
index c13f2bbfe..da903cf09 100644
--- a/src/lib/dcpomatic_time.h
+++ b/src/lib/dcpomatic_time.h
@@ -275,6 +275,10 @@ public:
 	bool operator== (TimePeriod<T> const & other) const {
 		return from == other.from && to == other.to;
 	}
+
+	bool operator!= (TimePeriod<T> const & other) const {
+		return !(*this == other);
+	}
 };
 
 typedef TimePeriod<ContentTime> ContentTimePeriod;