Retrieve the last MB of multimedia files.

Some multimedia containers (AVI, MP4, etc.) put important information like the frames index at the end of the files. Without that, previewing the files is pretty slow, because the previewing software needs to rebuild the frames index first. Also, previewing only works for the downloaded data at the beginning of the files (while VLC is able to preview every parts that have been downloaded, provided it can read the frames index at the end of the files). I suggest that FDM downloads the last MB (1MB? 4MB?) of the files as soon as possible when using multiple download sections, so that previewing the files is easier.
For instance, such a feature is implemented in the "DownThemAll!" extension for Firefox, and the user can specify how much data at the end of the files the extension should try to download (it's limited to 1024KB though, which is not enough for big files).