DFPlayer Mini - PCB Schematics - Decode MP3

Does anyone have a schematic of the DFPlayer Mini with its components on it?

How do they decode mp3s?

I would like to modify the PCB or create something similar, but I cannot find how they are decoding mp3s and from what I have been looking at any IC to decode MP3's seems to be far more expensive than the DFPlayer to begin with.

If I wanted to design a sound player shield that read from an SD card not on board, where / what should I be looking for?

I am super happy with the quality of sound coming from the DFPlayer Mini and even its interface other than the SD card is inaccessible.

Thank you for your help.

The chip on the DF Miniplayer does the decoding, under license from the MP3 folks.

https://www.aliexpress.com/item/32860342792.html?src=google&albslr=221442105&src=google&albch=shopping&acnt=494-037-6276&isdl=y&slnk=&plac=&mtctp=&albbt=Google_7_shopping&aff_platform=google&aff_short_key=UneMJZVf&&albagn=888888&albcp=2069223045&albag=83200626464&trgt=743612850714&crea=en32860342792&netw=u&device=c&gclid=EAIaIQobChMI89Czqtf74wIVGODICh2v-QAbEAQYAyABEgLi8fD_BwE&gclsrc=aw.ds

I can’t see how they make money selling these for $0.98 each, shipping for $0.13, less than the price of sending a postcard.

under license from the MP3 folks.

The MP3 patents expired in 2017 so they no longer have to a pay royalties.