It would seem to me that the Raspberrypi Zero would be a hilariously bad candidate for this.
Y'know, seeing as it doesn't actually have a dedicated physical audio output and all, and even if you manually populated the output for video/audio on the board, you'd still have to use one of those annoying TRRRS adapters because composite video and audio are shared by the same jack point in all the modern Raspberrypis. Or use some odd kludge of micro-HDMI->3.5mm stereo audio.
And, while it does have a small form factor, when built into a usable portable audio player, it could not possibly retain that form factor.
There's a reason why you don't see people building audio players out of products like this. At the end of it all, you end up with an inferior quality product at a greatly inflated cost.
[Saint]