Optimise checking of existing image data.

When checking existing image data go from the end backwards until
a good hash is found rather than from the start forwards until
a bad hash is found.  This is a lot quicker for long files but
may miss a corrupted frame somewhere (however unlikely this is).

1 files changed, 7 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index d808ddf3e..ee9ebfcb9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
 2015-09-03  c.hetherington  <cth@carlh.net>
 
+	* Quicker, though slightly less safe,
+	check for existing picture data; go back
+	from the last frame written until we
+	find a good one rather than going
+	through from the beginning until we find
+	a bad one (#519, #504).
+
 	* Add frame counter to progress
 	when transcoding (#111).