=MP4 (H.264 + AAC) format=

Use ffmpeg to convert files into MP4 format which is supported by most browsers and mobile devices:

720p resolution:
 ffmpeg -i test.mkv -c:v libx264 -b:v 2400k -g 14 -r:v 29.976 -profile:v main -vf "scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2" -c:a libfdk_aac -r:a 48000 -b:a 96k -f mp4 test_720p.mp4

480p resolution:
 ffmpeg -i test.mkv -c:v libx264 -b:v 1500k -g 14 -r:v 29.976 -profile:v main -vf "scale=720:480:force_original_aspect_ratio=decrease,pad=720:480:(ow-iw)/2:(oh-ih)/2" -c:a libfdk_aac -r:a 48000 -b:a 96k -f mp4 test_480p.mp4