MP4 files are the main high-resolution video files recorded by GoPro cameras, whereas LRV files are low-resolution, compressed versions of the same video. To convert an LRV file to MP4, you can use video converters, such as VLC Media Player, Quicktime Player, or Windows Media Player. However, keep in mind that converting LRV files to MP4 will result in lower quality videos compared to the original HD files.