When you access your GoPro's memory card, you'll see other video types next to the video files and maybe photos. Namely so-called .THM and .LRV files. These have no specific symbol and usually have a small file size.
If you are wondering what these files are on your GoPro and why they are created, we would like to tell you this:
For .THM files, this is a thumbnail of the video you see on the GoPro when viewed from the display.
This file contains a small preview video. The file is usually created when you use the GoPro app "Capture" or a video on the display of the GoPro.
You can delete both files when they are displayed on your computer. The files are not needed to play videos.
You now know the difference between THM files and LRV files on your GoPro.