Sone523mp4 Exclusive Online

First, I'll need to confirm the correct terminology. "Sone523mp4" doesn't seem right. Sony uses various MP4 codecs like HE-AAC, AAC-LC, or even MP2. Maybe there's a specific model or product associated with the number 523? Sony has MP4 players, maybe an old Walkman model? Checking up, Sony Walkman NW-Z523, yes, that's a real model. It was a high-end Walkman from 2010, supporting advanced audio codecs including MP4 files. The user might be referring to MP4 files specific to this device.