M3U is a file format for multimedia playlists. It contains references to media files for a media player queue. Entries list pathnames or URLs pointing to media resources. Each entry ends with a line break, separating it from the next. Some devices only recognize CR LF line breaks. M3U files are opened in media players like VLC, Winamp, and Windows Media Player. They state locations of included media files. They also describe attributes of the referenced files.
To create an M3U file, load a playlist in a media player like VLC. Save the playlist to an M3U file. To open an M3U, use a compatible media player. M3U files are not actual audio or video. They queue media for playback in players. Supported media players can open M3U files. If unable to open, update the player software. Also check the file is not corrupted. Choose suitable M3U editor to modify. Most popular are Playlist Manager, MediaMonkey and VLC. They allow creating and editing M3U files.
VLC Media Player
Winamp
iTunes