It seems that Apple Watch 4 only has the SBC codec for Bluetooth. So your 256k AAC files (or anything else) will be converted and end up being a lower quality sound (yes, that's all about the listener). Most people who are interested in semi-higher quality sound on Watch are stuck with this codec. My google search only showed SBC bluetooth on Apple Watch 4. Is it right to assume that even with AAC codec earphones, you still get a lossy conversion and lose the original 256k AAC quality? Are there any audio / bluetooth professionals out there who can confirm this? And yes, I understand that most people can't tell the difference, but there are some people who are in higher quality sound and want better sound without wearing an iPhone or an extra DAC while exercising. In fact, to think of all the things that are already in this clock, I would not dare to complain that it lacks high-end sound. Just ask 🙂 Thank you for your efforts.