duration of test clips

[martinfrombern]

usually when doing test encodes i do them on 1 minute part of an episode/movie (usually with selectevery(...) and 2pass x264).
i wonder are there any restrictions on a test clip duration below which x264 settings "don't have time to take effect", in other words is it all right to make test encodes on a shorter parts of the source (e.g. 5-15 seconds)?

[benwaggoner]

usually when doing test encodes i do them on 1 minute part of an episode/movie (usually with selectevery(...) and 2pass x264).
i wonder are there any restrictions on a test clip duration below which x264 settings "don't have time to take effect", in other words is it all right to make test encodes on a shorter parts of the source (e.g. 5-15 seconds)?
If you're doing 2-pass with PBR > ABR, you'll want to grab a representative sample of the content, so you can see how the codec will distribute bits between different kinds of scenes. Maybe 3-5 min, if carefully selected? This can be hard with shows, as the opening and closing credits can be quite atypical with the rest of the show.

Even for simple 1-pass CBR, I generally want to use at least 30 seconds so the buffer has a chance to get full. The shortest clip in my test library is probably 80 seconds.