Google showed support towards Android O users for more Bluetooth audio codecs like Qualcomm’s aptX and aptX HD as well as Sony’s LDAC to facilitate the high quality Bluetooth audio streaming for and on supported devices.
Under the use of the Developer Options, those who are on Android O Developer Preview can find different options to choose from among numerous Bluetooth audio codecs. Nonetheless, please advise that these codecs will not run properly unless the correct encoder libraries are installed. Case in point: it may appear that the Nexus 5X and Nexus 6P will not be capable to enjoy the advantages of the aptX after all.
If you did not know or were not made aware, aptX is a proprietary Bluetooth codec possessed by Qualcomm that permits supported devices to stream lossless, low latency audio to the devices that support Bluetooth enabled devices. Even though the both Pixel phones can support the codec, the Bluetooth audio codec is missing from the Developer Options on the both Nexus devices.
The first problem made its self appear at surface when a Nexus 6P used filed a bug report on the Google Issue Tracker page, where he stated that he was incapable to make the audio codec run on his device, to which a Google developer has answered back with the next message: “Unfortunately support for aptX and aptX HD are not supported on Nexus 6p and Nexus 5X – only on newer devices.”
So there is the proof; the two phones, Nexus 5X and Nexus 6P do not officially support aptX and aptX HD and, apparently Google has no intention in planning to make a support for them. It might be that Google is avoiding the potential licensing fees it should pay to Qualcomm if they ever decide to add support for its proprietary codecs on the Nexus 6P and Nexus 5X. Nonetheless, we will never find out the real reason until Google will officially provide a declaration on this problem.
We could say, unofficially though, that it could be possible to get the codecs run properly on these devices. Actually, there is already a Magisk module ready for use for the Nexus 6P that allows support for aptX.