Am I allowed to edit a track from freesoundtrackmusic so that the music synchronizes with my video?
Yes, it is OK to do sound edits on the music as long as you are not intending to produce a new musical composition. The music cannot be re-released in any other audio-only format, but if you are just doing fade-ins, fade-outs or cutting out smaller segments of the sound file to use as repeating loops within your video, it is not a problem. The main point is that the music available @ freesoundtrackmusic is for video or film production use only, and not to be used as a resource for further musical compositions. This stipulation does make music sourced from freesoundtrackmusic.com more restrictive than recordings which are released under some types of creative commons license (which may grant users the right to adapt and integrate the music into their own musical compositions), but at the same time less restrictive than other types, in that video producers can use the music in productions intended for commercial release. An important way in that the royalty free music from this site differs from all types of creative commons licensing is that if you are a registered user (or "member") of the service, attribution(telling your audience the name of the original composer) is not required.