Are you going to 720p video calls? 21st century in the yard but video resolution is still VGA.. ((
Zoiper supports resolutions of up to 1600x1200.
The limitation could be coming from your hardware or your PBX.
In video settings Zoiper supports follow formats: Low (176x144), Medium (352x288) and High (640x480).
Where is 1600x1200 ?
Probably this mode is not supported by your camera.
My front cam supports up to FullHD video. I can choose 720p for example in Linphone or AntiSIP software. So it works. But in Zoiper only VGA size.
Can you post a screenshot like my - http://images.vfl.ru/ii/1584893059/e2a22118/29968025.png
My mistake, I thought this was a question related to the desktop product.
On android there's a limit indeed due to the excessive battery usage and heat generation during calls.