THM files are THuMbnail files, which are often created by digital cameras. Digital cameras often make a THM file and an AVI file together with the same file name, but different file extension. THM files are made so users can view a thumbnail preview of the movies in JPEG format with a standard picture viewing software program. The THM files also contain all of the relevant data for the file, like where it was shot, the date and camera settings. THM files are not video files; therefore, they cannot be converted into a video format like AVI. But, you can locate the connected AVI or JPEG file and play that.
Open your "My Pictures" folder or another folder where your pictures and movies are downloaded from your camera and stored on your computer.
Search for the identical THM file name, except with the file extension AVI or JPEG.
If you can't find it, try performing a search of your entire hard drive by copying the name of the file and entering that name into the search box. Sometimes the files may be stored in separate or hidden folders.
If you still can't find it, then you have likely deleted the attached AVI or JPEG file. Try uploading the files from your memory card to your computer again.
If the files have been erased from your memory card, you can try running a recovery utility program from the "Utilities" menu. If you back-up your files, you can also see if the file is saved on your back-up disk or external hard drive.
It is wise to back-up all of your important files to a separate disk or external hard drive.
Do not delete your THM files, as some players require both files to view the video and play back the audio.