Fix black borders around the preview in some cases (#2331).

We need to round the container size to the nearest multiple of 2
so that cropping subsampled sources does not leave gaps.  As far
as I can see:

- the direction that you round x in doesn't matter
- it's better to round y up

(if you calculate the error in the resulting ratio in each case).

2 files changed, 11 insertions, 1 deletions

diff --git a/src/lib/video_content.cc b/src/lib/video_content.cc
index de3d3f3a2..1d1d010a9 100644
--- a/src/lib/video_content.cc
+++ b/src/lib/video_content.cc
@@ -660,7 +660,7 @@ VideoContent::scaled_size (dcp::Size film_container)
 	}
 
 	auto size = size_after_crop ();
-	size.width *= _sample_aspect_ratio.get_value_or(1);
+	size.width = std::lrint(size.width * _sample_aspect_ratio.get_value_or(1));
 
 	/* This is what we will return unless there is any legacy stuff to take into account */
 	auto auto_size = fit_ratio_within (size.ratio(), film_container);
diff --git a/src/wx/film_viewer.cc b/src/wx/film_viewer.cc
index b5b2ca972..c56e2f5d2 100644
--- a/src/wx/film_viewer.cc
+++ b/src/wx/film_viewer.cc
@@ -303,6 +303,16 @@ FilmViewer::calculate_sizes ()
 	out_size.width = max (64, out_size.width);
 	out_size.height = max (64, out_size.height);
 
+	/* Make sure the video container sizes are always a multiple of 2 so that
+	 * we don't get gaps with subsampled sources (e.g. YUV420)
+	 */
+	if (out_size.width % 2) {
+		out_size.width++;
+	}
+	if (out_size.height % 2) {
+		out_size.height++;
+	}
+
 	_player->set_video_container_size (out_size);
 }