I have a number of mkv files that are 2:35 that I would like to convert to 16:9 (1280x720) for playing on the Kindle Fire HD. I tried to accomplish it using Mkvtoolnix but it never seems to save the changed aspect ratio because it's always back to normal when I transfer and then play the file on the Kindle. For some reason, the aspect ratio change works when playing the changed file on VLC on the computer but it doesn't keep the change on the Kindle. I also tried to use Subler but whenever I try to change the aspect ratio the resulting video looks way off when testing it with VLC. What am I doing wrong or is there another program that would more successfully do this?