If you guys are still struggling with this issue, I may be able to help.
When sending video, Zoom requires you to send frames that match one of the “capabilities”. A capability consists of a width, height and frame rate. If you send images whose dimensions do not match one of the capabilities, the SDK call will succeed but the image will be cropped.
The SDK will give you the available capabilities when you initialize the virtual video source. Unfortunately, by default it seems like the highest available resolution is 640x480. However, judging by this post, it looks like you can write into customer support and get 1280 x 720 activated for your Zoom account. See here
and here
I came across this issue when adding the output image functionality to an open source meeting bot API I am building called Attendee. You can check it out here: GitHub - noah-duncan/attendee: Meeting Bots made easy
It may save you time over working with the Linux SDK directly.
If you just want to see the code that fixed this issue, here’s the PR for it: In Zoom image output, scale image based on video cap size by noah-duncan · Pull Request #129 · noah-duncan/attendee · GitHub