From 2d9f569c146b391159f362c854457ce1facac1e8 Mon Sep 17 00:00:00 2001
From: Carl Hetherington <cth@carlh.net>
Date: Wed, 7 Jun 2017 21:27:40 +0100
Subject: [PATCH] Fix crash when alpha-blending subtitles onto YUV420 images.

---
 src/lib/image.cc        | 10 ++++++++++
 src/lib/image.h         |  2 ++
 src/lib/player_video.cc |  2 +-
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/lib/image.cc b/src/lib/image.cc
index b82cc6072..03a4d96b4 100644
--- a/src/lib/image.cc
+++ b/src/lib/image.cc
@@ -1035,3 +1035,13 @@ Image::fade (float f)
 		throw PixelFormatError ("fade()", _pixel_format);
 	}
 }
+
+shared_ptr<Image>
+Image::ensure_aligned (shared_ptr<Image> image)
+{
+	if (image->aligned()) {
+		return image;
+	}
+
+	return shared_ptr<Image> (new Image (image, true));
+}
diff --git a/src/lib/image.h b/src/lib/image.h
index fd5adb076..9a5a7dae8 100644
--- a/src/lib/image.h
+++ b/src/lib/image.h
@@ -77,6 +77,8 @@ public:
 		return _pixel_format;
 	}
 
+	static boost::shared_ptr<Image> ensure_aligned (boost::shared_ptr<Image> image);
+
 private:
 	friend struct pixel_formats_test;
 
diff --git a/src/lib/player_video.cc b/src/lib/player_video.cc
index 2e53a6aa6..6f0977e62 100644
--- a/src/lib/player_video.cc
+++ b/src/lib/player_video.cc
@@ -135,7 +135,7 @@ PlayerVideo::image (dcp::NoteHandler note, function<AVPixelFormat (AVPixelFormat
 		);
 
 	if (_subtitle) {
-		out->alpha_blend (_subtitle->image, _subtitle->position);
+		out->alpha_blend (Image::ensure_aligned (_subtitle->image), _subtitle->position);
 	}
 
 	if (_fade) {
-- 
2.30.2