Increase number of frames stored in memory before write (#748).

2 files changed, 12 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index 0cdf8131b..ec4c1c988 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,7 @@
 2015-12-21  c.hetherington  <cth@carlh.net>
 
+	* Reduce frequency of temporary writes to disk (#748).
+
 	* Use new Dolby website for both Doremi and Dolby certificates (#775).
 
 2015-12-18  c.hetherington  <cth@carlh.net>
diff --git a/src/lib/writer.cc b/src/lib/writer.cc
index 93f5ed6d6..47c6b8381 100644
--- a/src/lib/writer.cc
+++ b/src/lib/writer.cc
@@ -570,7 +570,16 @@ operator== (QueueItem const & a, QueueItem const & b)
 void
 Writer::set_encoder_threads (int threads)
 {
-	_maximum_frames_in_memory = lrint (threads * 1.1);
+	/* I think the scaling factor here should be the ratio of the longest frame
+	   encode time to the shortest; if the thread count is T, longest time is L
+	   and the shortest time S we could encode L/S frames per thread whilst waiting
+	   for the L frame to encode so we might have to store LT/S frames.
+
+	   However we don't want to use too much memory, so keep it a bit lower than we'd
+	   perhaps like.  A J2K frame is typically about 1Mb so 3 here will mean we could
+	   use about 240Mb with 72 encoding threads.
+	*/
+	_maximum_frames_in_memory = lrint (threads * 3);
 }
 
 void