Bluetooth input for video recording : Android 10, One Plus 7 I have seen this question Record video with external bluetooth mic (ie headset) posted 8 years back and app solutions do exist but not with Android 10,so it's not a duplicate of this question or other questions which suggest apps (they don't work for me) 

I am helping my wife  record instructional videos on OnePlus 7, running stock Android 10 (not rooted). 

I want to use Bluetooth audio input instead of the device mic, as it would provide better flexibility. 


I don't find any settings to enable Bluetooth in camera or elsewhere and internet search hasn't helped.
Blogs recommend apps but surprisingly none seem to work reliably with Android 10. BTmono works sometimes and is not a reliable solution, and similar story with Camera fv5 


Any suggestions, including apps, accessories are welcome except


Separately recording audio and sync with video, that's too much work
Involving signal processing hardware 
Root
Laptop 
Accessories like mic (I have asked for accessory advice on SE.Video Production 
and hope to get better answers there)
Finally cracked it! Using any Bluetooth headset (even supporting BT 5.0) like Crossbeats
and recording with stock camera app or with Open Camera with audio source set to external doesn't work.

Solution

I had a Bose BT2 Bluetooth headset, which I haven't used in the last 7 years and surprisingly charged up and gives me about an hour of usage time which is more than enough. I wanted to use this to improve the quality of recording since it has excellent noise cancellation. You may as well pick up any recent BT headsets of your choice and of recent vintage. Profiles supported by Bose headset are
HSP, HFP, A2DP - SNK, AVRCP

Download Bluetooth Mono Router. Blogs and YouTube videos recommend BTmono but it hasn't been updated for Android 10 and won't work. Both these apps have the same functionality - they let you play BT audio to those old headsets which only support voice calls and not media. I am not clear as to how this let's you overcome the limitations of recording but it works and asked a question here.You can use either stock camera app or Open Camera (audio as external in settings)

In case you can't record, activate developer options and from Bluetooth settings try AVRCP 1.3 and SBC codec combination (you need to enable Bluetooth to be able to change these settings). These seem promising. In my case I used default.


Tip: Make sure to disconnect Bluetooth when playing back the video, else, you may find no / low audio and think it doesn't work

Permit me  a little rant about One Plus tech support with interactions over several mails. YMMV. Documenting it just in case it helps others.

They do not respond when you ask them how to record using Bluetooth.

Using wired Lavalier solutions need an extra adapter in some cases and even then no guarantees. Reason : Non standard implementation of USB C to audio adapter (Shades of wrong resistance used in early models)
. They claim on mail that TRRS is not supported , being a third party affair and when confronted with standards do not reply