I have used Shield TV devices in my home twice, and both times found I had to use IR Volume control rather than the more reliable CEC method because with CEC you get just one Volume step for each press, so you must "pump" to change the Volume significantly, as opposed to IR, where it smoothly changes in the desired direction until you release the button. Is there any way to make CEC work like IR in that respect? Why do the developers think we want CEC Volume to work the way it does -- makes no sense? And it is the same whether using the Shield remote or a Fire TV remove via BT, so it is not a function of the remote itself.
In my setup holding the volume down via CEC produces continuous change as you describe. So, this probably isn’t a global problem, and may depend on how your audio device has implemented CEC.
Sorry to hear that, both my current Marantz and previous Yamaha just do single steps on CEC.
Our app has no control over CEC or volume, it's all handled by Android OS