APT-X is a proprietary codec that performs far better than the original bluetooth audio codec & can be used for things that said codec really was’t up to. (It also includes a lossless mode for the audio purists amongst us.)
Modern bluetooth devices can also negotiate various other codecs as part of the A2DP spec: https://en.wikipedia.org/wiki/List_of_Bluetooth_profiles#Adv... including mpeg3/mpeg4 encodings but only SBC is mandatory and it seems to be impossible to tell what codec any particular Bluetooth audio device is using on any platform: I’ve not seen anything that will tell you what it’s really sending over the air.
If you're able to test with an Android device running 4.4 or later, you should be able to turn on Bluetooth Logging in Developer Options.
Wireshark can read bt_hcisnoop.log as a Symbian OS Bluetooth Log (really). From a bit of fiddling you're looking for a series of AVDTP requests with GetCapabilites (to your speakers/headset/whatever) and then SetConfiguration (from your phone/player). Filtering by btavdtp.service will get you this.
I can tell you my phone is ignoring SBC and AAC support and asking for APT-X only.
That is impressively convoluted. I have a feeling it ought to be possible to write a gstreamer plugin to do this, but it’s one of those minor projects that never got over the do-I-care-that-much hump.
I've got a feeling that by the time an audio stream gets to GStreamer it's not in the original format. Also you'd have to get an A2DP sink working (to make your phone think the computer is a headset / speaker)
Modern bluetooth devices can also negotiate various other codecs as part of the A2DP spec: https://en.wikipedia.org/wiki/List_of_Bluetooth_profiles#Adv... including mpeg3/mpeg4 encodings but only SBC is mandatory and it seems to be impossible to tell what codec any particular Bluetooth audio device is using on any platform: I’ve not seen anything that will tell you what it’s really sending over the air.