How to convert .mpcpl playlists to .mp4 format.
Converting Media Player Classic Playlists directly to MPEG-4 Videos (.mpcpl to .mp4 conversion) is not possible, since MPCPL files are neither audio nor video files.
If you want to convert media files, referenced by your MPCPL playlist, to other formats, you must first locate/download those files. You can then easily convert those files using most available media editing programs or (online) conversion tools.
In a word, direct mpcpl to mp4 conversion is not possible.
So don't expect any so-called mpcpl to mp4 converter or mpcpl to mp4 free online conversion tool available.