Remix Video Frame Size and Resolution
Choosing appropriate frame size and aspect ratio for your remix video project can be a tricky complicated business. Since most video remixers are making their work to display primarily on the web here are a few things to consider:
1) The dimensions of the original media sources
Many remixers find themselves using footage from a wide variety of available sources including DVD rips, Blu-Ray rips, downloaded iTunes or Amazon files, downloaded AVI or MKV files, downloaded YouTube or Vimeo files and homemade screen captured video. Because all these video formats will likely have various frame sizes and aspect ratios its important to take a look for the lowest common denominator. If you are working with only one media source or if all your footage is HD via downloads or Blu-Ray rips then your remix project can easily match the source footage at 1280x720 (720p) or 1920x1080 (1080p). If you are working with ripped US DVDs in your project its a little more complicated. Your project should probably be closer to 480p and match the DVD frame size - most likely you want 854x480 (anamorphic widescreen) and 720x400* or 640x360 (widescreen) and 640x480 (fullscreen). However (since video does not typically upscale well without significant pixelation) if you are incorporating a bunch of lower resolution YouTube or web video clips into your remix you might pick smaller overall frame size to work in like 640x360 or 320x180 (windscreen) and 480x360 (fullscreen). YouTube also has some very basic suggested frame sizes.
2) Cropping the original footage to isolate a character or event
Remixers may also choose to work in a frame size significantly smaller than the majority of their original source media so as to have the option for footage cropping or zooming. This process works best with 1080p or 720p HD footage which can then be cropped down to 480p or 360p in order to focus on or isolate various elements and characters within the frame (without loosing video quality) in the final remix.
Below is an example from my current Batman Reimagined remix project where I want to focus on Batman’s words and remove the Joker from the scene entirely.
Original 1080p footage: 
Cropping down to isolate Batman: 
Resulting 720x400 crop:
*Technically the math for 720px DVD 16:9 windscreen works out to a height of 405 which then has to be changed to an even number (either 404 or 406 depending on who you ask) BUT most video codex work best with multiples of 8 or 16 so 720x400 seems to be best for web video even if the aspect ratio is off by a few pixels.
