Stitching videos together with in/out points

I'm working on a project that basically stitches videos together.

I need something a bit more complex than cat as I need to set in and out points of the video.

Say I needed to render out the following:

1. Video1 (using the clip from 10seconds-20seconds)
2. Video2 (using the clip from 5seconds-7seconds - fade in from video1

My thinking would be:

• Render out version of video1 from 10 seconds in to 20 seconds out
• Render out a version of video2 from 5 seconds to 7 seconds
• Stitch the videos together with transition.

I've had a look at mencoder/ffmpeg and I think I may need a combination of them. I'm not sure where to begin on transitions between clips though - any advice on routes to take would be really appreciated.

I need to be able to run this from a linux command line.

AVI Synth and FFMPEG worked well in achieving this task... http://avisynth.org/mediawiki/Main_Page