I just learned something tonight after wondering what where those LRV and THM files on my GOPRO HERO3. Turns out the THM is just a JPG used in the future as a thumbnail for the video and the LRV is a super low res version of the video (432x240). I'm assuming the latter is for playback via wifi or simply as the streaming buffer when the smartphone is used as control. If you want to see this, just rename the THM to jpg and the LRV to MP4.
It's also kinda neat/freaky that each MP4 has your camera's serial number embedded into it. And you know when you update your camera and register it, you're serial number is tied to you. However, whenever you edit your video this stuff gets trashed. But it is good to know!