Create Video: always pad video to even sizes

H.264 requires that the width and height of the video frame are
multiples of the chroma block size. When using the default yuv420 pixel
format this means the dimensions should be even (e.g. multiples of 2).
The video filter added in this commit ensures this by padding out the
frame with black pixels.

flamenco_worker/commands.py

@@ -1239,6 +1239,7 @@ class CreateVideoCommand(AbstractFFmpegCommand):
             '-c:v', self.codec_video,
             '-crf', str(self.constant_rate_factor),
             '-g', str(self.keyframe_interval),
+            '-vf', 'pad=ceil(iw/2)*2:ceil(ih/2)*2',
             '-y',
         ]
         if self.max_b_frames is not None:

tests/test_commands_create_video.py

@@ -67,6 +67,7 @@ class CreateVideoTest(AbstractCommandTest):
             '-c:v', 'h264',
             '-crf', '23',
             '-g', '18',
+            '-vf', 'pad=ceil(iw/2)*2:ceil(ih/2)*2',
             '-y',
             '-bf', '0',
             '/tmp/merged.mkv',