I've taken the liberty of changing the thread title to something more descriptive.
No such thing. The replay file saved to USB is not a video, just the data the game went through while you played what it recorded. All that happens when you view a replay in the game is the game plays it, taking inputs from the file instead of the controllers. It re-renders the replay from the data every time you play it.
You wouldn't have enough memory to save a video file in an 8MB memory card. Just look how big even crummy video files are.
Can't you save the file directly to a USB stick?