AVI to mpg conversion for use in VIPER

[annie]

Using AVI files needs them to be converted to mpg or image
sequence.Images sequence needs a lot of space to store for full
movie.So it will be a nightmare to store the image sequence of many
movies together.
When I use mpg encoder I lose some frames or the frame rate or frame
size is changed.

Could anyone tell me the mpg encoder which doesn't change the frame
rate and frame size of input AVI file.

Thanks!!