720p vs 1080p

As a rule of thumb, to be able to see the full benefit of 720p, one should sit at a distance from their HDTV 5x the height of the HDTV. For 1080p, it will be 2/3 of 5x, i.e., 3.3x. For instance, if the screen size is 100", the height of the screen will be 49" or 4.0855 feet. To view 720p, you need to sit 20 feet away. To view 1080p, you need to sit 13.3 feet away, which is a good distance for people who has a front projector. If you have a 50" HDTV, to view 1080p, you need to sit 6.7 feet away, which is not practical and comfortable for most people. If you have to sit more than 10 feet away from your HDTV, 720p is enough.
Note: Use MediaInfo to find technical and tag information of video or audio files; Use MKVToolnix to join mkv files.