I take it then that mp4 and mkv are simply containers, correct? I have some questions. The first involves file size. I just looked for a typical movie (about 1:45 in lenght) and noticed that using Matroska the file size was about 2 GB - with a resolution of 720p. A similar movie encoded with mp4 takes up about 1.5 GB with a 1080p resolution. Imagine you had the same movie in 1080p format, one copy as mp4 and the other mkv with a much larger file size. If you put both on flashdrives and played them side by side on 2 similar TV's, would the mkv look better?
I've seen the webm format on some files. MPC-HC plays it perfectly.