I noticed on some of my Bluetooth audio devices mainly my earphones there was a delay when watching video, this could be local or streaming like YouTube, iplayer etc. On some apps you can adjust the latency audio forward or back. This is a pain if you use different headsets as you need to keep adjusting this.
I mainly noticed this on my Samsung Note tablet and phone, It turns out its to do in my case that is the GPS chip is interfering. This may work with others that are having problems with Bluetooth lag / delay.
To turn off Bluetooth on Samsung devices go to settings->connections-> more connections and turn off Nearby scanning.
If on plain android like I am on a custom ROM on my Samsung devices go to settings->location and turn off
For me turning this off worked for others it may not, I have heard that turning on Force GPU Rendering under developer options. To do this first if you havn’t got developer options under Settings. You need to enable Developer options this is done by going into settings->about device then tapping on build number 7 times, then under your settings you will have developer mode.
Within developer mode scroll down to “hardware accelerated rendering” and enable Fore GPU rendering.
The first option worked for me, if not try the second option. If still not working for your device, there may be other fixes, would recommend searching your device and audio lag as some great forums out there.