Instaplay optimizes mp4 files for instant start streaming. The top mp4 encoders don't optimize for streaming by default, and would require another round of encoding to optimize- taking time, and at a loss of quality.
Instaplay reorganizes the existing movie data allowing instant streaming, without any further degradation. It is safe to use on any movie file, if the file is already optimized or the file format isn't recognized, they are skipped. Using Instaplay is as easy as dragging the files to the Instaplay window or Dock icon. All files are then queued up and processed. Instaplay is fully sandboxed for your protection. As the file is optimized it is saved to your 'Movies' folder.