Fair use is annoying vaguely defined in the law. This means media companies will tell you that's it is so limited as to be almost useless, while the EFF and the courts may disagree. You may hear stuff about "10 second clips are the max allowed by law", but the law doesn't draw any clear likes like that and in fact is usually much more generous. Typically quotes like that come from a single precedent where someone was acting outrageously in many other ways and not relevant precedent for what you're doing.