>>1553917DIN barrels have a just over a half inch diameter.
That definitively tells you that it is also nothing to do with a C64. I don't think Commodore even used 5 pin DIN to RCA, it was 8 pin DIN using separate luminance, yellow to pin 1 but yours is to white, and chrominance, red to pin 6 but that doesn't even have a pin 6 and red is connected to pin 5.
It could be a luma + chroma + mono audio device or a composite video + stereo audio device, like a VCR, laser disc player, amplifier, receiver, game console, camcorder.
From an opinion point of view, an a/v device that supported chroma and luma channels probably, unlike the C64, used stereo audio too because separate video channels were a mark of high end personal use or professional equipment and you wouldn't expect mono audio there. With 3 plugs it's more likely some sort of home use composite video + stereo audio device.
Nothing special about that cable. If you chuck it away and find what you think it's needed for you can make a replacement with off the shelf components if you couldn't buy a replacement.
