So
Kelly, Here's my take.
Not trying to step on your thread Bernd
Jaeger.
Make it possible to position the videos or images using
corner pinning. That would mean no background, just the placement of the image
or video. As an Add-On to Device Frame. I tested and confirmed that the Device
Frame feature already utilizes corner pinning. So maybe it wouldn’t be too hard
to separate the features?
Why? You can take a photograph of a 16 x 9 computer monitor,
I-Phone, Tablet, picture frame, etc. However, due to the tilt of say, a monitor’s
screen. Coupled with the angle of the camera that’s shooting the picture. That
creates a skewed and/or distorted image of the monitor that is incapable of properly
framing a 16 x 9 video. “Within the monitors screen area” Some corners of the
video would either need to appear outside of the actual screen area, or be
pulled back from the edges of the screen area to fit. Either way you go, it
doesn’t look good or professional.
To ensure Device Frame was corner pinning. That
the images included with Camtasia weren’t just very strategically shot for Device
Frame. I created a 16 x 9 image with a five-pixel red border.
Then I put the image in Photoshop and placed guidelines to
prove or disprove that the monitor was in fact out of square. “They always are” but I wanted
to be sure.
If you
look in each corner, you will see that each corner of the image had to be moved dissimilar distances,
in 2 directions as well. Also, not one pixel of that five-pixel red border has
been cut off in the process. So in essence, it’s been distorted into place. It's not placed behind a png cutout or anything like that.It's done right.

Currently
you can only use Device Frame on one piece of media at a time. Perhaps with
corner pinning it could be expanded to work with multiple videos or images?
Here’s an example of Adobe’s Premier Pro. You can see the blue target handles
highlighted. You simply drag them into position and that’s it. The left monitor is already corner pinned with a separate image.
If Camtasia users could do that too. The skies the limit.

Regards,Joe
Kelly Rush, Product Manager
Love the ideas going on here as far as allowing custom content; it's certainly something we'll consider for the future.
One additional point you might be interested in, since you're digging into the technical aspects, is how we approached still vs. video. We did a TON of research into what we thought would make for good Device Frames in Camtasia, including watching quite a bit of existing examples. One thing we noticed was that some of the best content used backgrounds that LOOKED still, but when you watched it, they had subtle motion happening; lights moving here, a person's head tilting there...it just made the content slightly less static, more like what you'd see in the real world. We went to some pretty great lengths to replicate that effect, not sure if it's something that MOST people could/would want to do when creating their own, but certainly something we felt was worth the extra effort.
Cheers,
Kelly