And some more useful AVI capture tips:
1- record a demo first, then play it back to capture the AVI;
2 - if your engine allow to set the AVI fps, use something as low as the host ticrate (usually 10Hz when model interpolation is disabled, 15 if enabled);
3 - also, set low screen dimensions (my default is 512 x 384, which gives a more than enough good resolution for YouTube videos).