Hopefully fix crash when the same frame is encoded twice.

Previously if some frame X was passed to the encoder twice
I think this would happen:

X1 written; X stored to _pending_images
X2 written; _pending_images remains the same
X1 encode finishes; X is discarded from _pending_images
Data for X2 is read by the encoder but was just freed

I think this might have resulted in intermittent crashes, which were
fairly common in the 2.17.x branch with the test
ffmpeg_encoder_prores_regression_1

But I didn't conclusively prove it.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/lib/ffmpeg_file_encoder.h b/src/lib/ffmpeg_file_encoder.h
index 5bf501370..f0b3eac8c 100644
--- a/src/lib/ffmpeg_file_encoder.h
+++ b/src/lib/ffmpeg_file_encoder.h
@@ -106,9 +106,10 @@ private:
 	std::shared_ptr<AudioBuffers> _pending_audio;
 
 	/** Store of shared_ptr<Image> to keep them alive whilst raw pointers into
-	    their data have been passed to FFmpeg.
+	    their data have been passed to FFmpeg.  The second part of the pair is
+	    a count of how many copies of the same key must be kept.
 	*/
-	std::map<uint8_t*, std::shared_ptr<const Image>> _pending_images;
+	std::map<uint8_t*, std::pair<std::shared_ptr<const Image>, int>> _pending_images;
 	boost::mutex _pending_images_mutex;
 
 	static int _video_stream_index;