The file extension M1V denotes video files in the old MPEG-1 compression method. It is a lossy process limited to a data rate of 1.5 Mbit / s. So-called VideoCDs were usually created with MPEG-1.
However, M1V files only contain the video stream. In principle, most video players and editing programs should be able to handle M1V files. However, if the extension M1V is not recognized or it does not appear in the file selection, changing the extension to mpg may help.