The Pink Floyd Synchronization phenomena suggests an intriguing and technically challenging method for compiling a mix-tape or disk; one which I'm increasingly tempted to have a crack at.

When compiling mix tapes in the past, I've frequently thought of the mood and pace of the tape in filmic terms (although this works better for disks because with tapes you have to flip sides in the middle of act 2); always searching for the soundtrack to the film I'll never make.

Instead of trying to be uncompromisingly original, the auteur of one's own mix tape, how about a mix tape that's synchronised to somebody else's movie? An alternative soundtrack?

The Challenges

There are several factors in this that must all be considered and balanced. Timing and tone must be considered in parallel such that the track playing at any particular moment both fits the scene and ends in a timely manner (you don't want thrash metal bleeding over from an action sequence into a gentle romantic scene, for instance. Plentiful use of short songs and segues is probably the best option for fine-tuning.

Two timing complications are synchronisation and overall length. Depending on how accurately you want your mix to tie in with the movie, you need some event at which point the mix should begin. Simply "Press PLAY on the VCR and tape deck simultaneously" only works for one distributed form of the movie, and lead-ins on VHS tapes vary from print to print. A good cue is probably the Studio's banner; every film starts with one. Pink Floyd used the MGM Lion as their synchronisation event.

The overall length is another source of problems. If your movie lasts less than an hour and a half, you have enough space on a C90. But if you're using CD or MD as your medium to avoid side-flipping, you're limited to 72 minutes. The result is either unaccompanied footage at end of the movie, or you have to put the audio on repeat. The challenge this presents is that the music must be timely and appropriate for more than one scene. This is far easier if the length of your mix is calculated so that key scenes of a similar nature are covered by one track. (The best overall length for your mix is thus given by the term having the highest coefficient in the Fourier series describing the intensity of mood throughout the movie; but I digress... almost constantly, as it happens...)

Choosing Your Movie

Things to consider when choosing your movie:
The wider the audience that know the movie, the better; if you want to give copies to your friends, it's not going to help if the movie is so obscure (or, conversely, so popular) that your friends aren't going to know of it, or own a copy.
Quality and Endurability
It also has to be something that can be watched again every so often. Pink Floyd's choice of The Wizard of Oz was a good one because everyone's seen it, almost everyone likes it, and it can easily played be once in a while without getting sick of it.
Forgettable summer popcorn muncher hits are unlikely to fit this bill.
Existing Soundtrack
If the existing soundtrack is in a similar vein or is arguably superior to the one you intend making, that would diminish any sense of achievement you might get, or sense of awe you'd inspire in others. Trying to engineer a new soundtrack for Pulp Fiction, for instance, is an exercise in futility since the original one is so well fitted to the movie.
Yet again The Wizard of Oz seems a good choice; it's scenes are fairly long so it's easy to match a song to each scene. Short scenes need shorter songs, more bleedovers, more segues to keep time.

Pink Floyd at least had the luxury of producing their own songs, and could easily make small adjustments to track length; not so for the rest of us.

The pace of the movie also makes requirements on the precision of your timing. The Wizard of Oz, with its long, lazy fades between scenes, allows significant slack time between track changes. Rapid and dramatic scene changes are less tolerant.

At this moment in time, I'm considering Plan 9 from Outer Space as my target movie; it's reasonably popular, short enough to cover with a single 80 minute CD (though not an MD, phooey), it's long narrative periods should give some slack for sloppy timing, and plus I kinda have this vision of zombies lurching around to Papa Roach's "Infest".

If I ever actually get around to doing this, I'll be sure to post track lists :-)

And remember...

The mix should stand on it's own, independent of the movie. If it's a random slapdash of mediocre songs chosen because their track length happened to be right, the only value it will have is novelty value. Dark Side of The Moon is a classic in it's own right. It doesn't have to be watched in time with the movie (and I'll warrant 99.99% of those who own a copy have never done that). The Wizard of Oz synchronisation is just an obscure added value feature.

It stands on it's own, and that's what we should aim for too.