Cherry pick cbbc75a40156be9e3ef777e0f060f23639025e60 from master to fix slow exports.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/lib/image_proxy.h b/src/lib/image_proxy.h
index 846aec136..b377d5362 100644
--- a/src/lib/image_proxy.h
+++ b/src/lib/image_proxy.h
@@ -80,7 +80,7 @@ public:
 	 *  This method may be called in a different thread to image().
 	 *  @return log2 of any scaling down that will be applied to the image.
 	 */
-	int prepare (boost::optional<dcp::Size> = boost::optional<dcp::Size>()) const { return 0; }
+	virtual int prepare (boost::optional<dcp::Size> = boost::optional<dcp::Size>()) const { return 0; }
 	virtual AVPixelFormat pixel_format () const = 0;
 	virtual size_t memory_used () const = 0;
 };