I don't think there is any set length, but the spirit of the law seems to be that if you do borrow from a copyright source, you must surround it with commentary that is longer than what you are borrowing.

For example, if you show a 1 minute clip from a film, try to put more than a minute's commentary about the film before it and after it.

If you watch professional movie reviewers on TV, they'll normally talk about a film for a few minutes, then show a short clip that's maybe half a minute, then talk for another few minutes, and the clip itself is normally only maybe 10% of the overall review running time.

If there are any lawyers here, they're not going to give a legal opinion from reading a forum post - there's no way to know all of the necessary details, and the law differs depending on where you live. So if you want legal advice, you'll need to get it from a knowledgeable attorney in your locality. The following are just some thoughts -

Continuing the parallel to book reviews, what you show of the movie should directly relate to your comments. For example, in a book review you wouldn't use a paragraph of narrative to illustrate how a writer handles dialogue - you'd use a bit of dialogue. I don't show clips on any website, but on one site that deals with specifics of acting and movie-making I do use individual frames to illustrate certain points, taking care to choose frames that illustrate those points. For example, commentary on how a cinematographer uses a camera angle to influence how the audience sees a particular character might show a frame using that angle to illustrate. (It's more fun and less formal than it sounds - My aim is to have it all flow together.)

With a general review, you probably wouldn't have to be so specific, but some tie-in with your commentary is a good thing, not just from copyright considerations but because it "backs up" your comments and shows you're a reliable reviewer. The TV reviewers are usually fed the clips for the purpose of showing them and have permission to do so, therefore don't need to worry about fair use or other copyright infringement considerations. But even in their reviews, you'll notice they usually find a way to tie the clip in with their comments. (If you check out the "press" area of movie company websites, you might find material that they'll give you permission to use to publicize a movie - provided you follow their rules and fit their definition of "press".)

Not sure how this applies here but to obtain clips from a DVD you'll have to break the law to begin with. You may be entitled to use some of the content under fair use but you need to break the CSS encryption to obtain it in the first place which as far as I know is not legal under any circumstances.

If you put the clips on youtube, instead of your own site, then people can look at the clips without the commentary. You would need to put them on your own site.

I'm thinking of doing a movie review site that will include clips. But how much per clip? And how many clips?

You would probably be better served by directing those questions at the source from which you intend to get the movie clips. I am presuming that you will be looking to make contact with the film/DVD promoters and distributors... They will be able to advise as to what is standard for review purposes and, indeed, are exactly the people to supply you with the very clips you need.

Syzygy

Per above, PR firms will provide trailers and clips. You would not be able to make your own without grabbing an illegal copy (if a new release) and then editing a clip out of that.

You should seek out the press sites for the various studios and attempt to contact the larger PR companies who also rep them.

No studio will take kindly to unofficial clips. Not even a matter of what is fair use just do you want a relationship with the studio concerned...if so need to follow their rules.

[edited by: FattyB at 2:27 pm (utc) on Feb. 22, 2008]

Make your life easier and just link to clips already provided by the movie studios.