Bluetooth Audio AAC codec quesitons 2018-12-15 02:17:16 I'm not sure what the appropriate forum is for this question, so I will leave it to the mods to move to appropriate forum.It is a well known fact that Bluetooth audio is unable to transmit music data in a lossless format (By lossless I mean 16/44.1. 16/44.1 is obviously lossy when compared to a 24/96 studio master, even though the two files are transparent). Because of this, lossy audio codecs are used to compress the data. SBC is the required codec by the Bluetooth spec, but other optional codecs such as AAC and AptX are supported.In the world of computer hardware Apple has standardized on AAC as it's preferred codec for Bluetooth Audio. They do not support AptX or LDAC. And Android devices also support AAC and SBC in the default Android install and vendors have added AptX and LDAC support to some hardware.Proponents of AptX claim it has much lower latency, and is therefore superior to AAC, because the use of AAC can cause audio and video to go out of sync.So, here are my two questions.If I have a Bluetooth 4.0 headphone connected to a phone or other Bluetooth transmitter, and I know for 100% certianty that both devices have negotiated AAC as their codec of choice, and then I choose to play a file that is already encoded in AAC, will the AAC file "pass through" to the destination devices or will Bluetooth re-encode the AAC stream?I know when Apple created the iTunes store, they originally released all tracks in AAC, and from what I read they have a license that allows them to use AAC is all their products. So, going with AAC over another codec was probably a pretty good cost savings for Apple. Since Apple sells tracks in AAC format, if Bluetooth over AAC just passes through the AAC encoded audio, I tend to think that this would save on CPU and/or battery. Is this a possibility?As for latency, I have NEVER had a video on my iPhone using YouTube, Hulu or Netflix ever go out of sync. Is Apple somehow compensating for the latency in software, or is the latency somewhat diminished by AAC audio pass-through.And last question... If latency is an issue with Bluetooth, why is no one using Opus over Bluetooth? Isn't one of Opus' goals to be a low latency codec?