If you are seeing that your MP2 is showing a different length than your original file, have no fear. This is an issue with MP2 encoding that happens to the metadata. The file itself is fine and is the correct length, however, it will sometimes appear to be shorter or longer in length in the metadata only.
Hindenburg has created a new and improved encoder for PRX that you can download for free! Head here for more information on the encoder and a video tutorial.