Avisynth to select parts

Well this should do the magic when you want to see if what you are encoding has the right lines...

Trim(1000,168438)
SelectRangeEvery(4000,250)

Trim: The first value of Trim should be the starting Frame of the movie. I mean after showing the starting credits. Then second value is before the End Credits start. You can get these frame numbers by opening your script using AVsP and using the Bar to move your video from starting to end. Alternatively you can select a particular scene by using the starting and ending Frame number of that scene.

SelectRangeEvery: In this example, 250 frames will be encoded every 4000 frames. So frame 0-250, 4000-4250, 8000-8250, etc., would be encoded. You can adjust those values as you please to encode a larger or smaller portion of the video. Just change the two values so that you end up with a 5 minute sample. Change the numbers and use the bar to see how much video time have you selected.