Commander X16

Do we have any figures on what the average amount of pixel rows/columns are lost to overscan when the VERA is connected to a TV?

I ran some numbers based on what my NES shows me on my CRT TV, and when I convert everything to the VERA's output timings (640x480 NTSC mode), I get this:
Top: 34 rows
Bottom: 28 rows (EDIT: original value 31 was a math error)
Left: 35 columns
Right: 56 columns

For reference, my measurements on the NES are T:16, B:12, L:8, R:12, so I just assume a 16-pixel margin all around the screen for not putting important stuff in. The NES has a pixel aspect ratio of 8:7, and the active picture region has a fair amount of a border on the left and right.

On the VERA, the pixels are very close to square (54:55, if I calculated it right), with absolutely no border; the active picture region is porch to porch horizontally, hence why there's much more lost to overscan here.

If anyone has physical hardware, do these numbers seem right?

I don't have the answer to your question, but in case you're asking because you're worried about the picture being cut off, in the kernel recently there were added some additional screen modes which are "safe" for CRT TV's/monitors, which add a border. This results in less rows/columns available however (in the editor, not pixels). The closest to the default 80x60 mode is probably mode 8, which is 64x50.

I worked with Adrian Black recently to get our VERA 15KHz modes timing as accurate as possible. The action safe and title safe areas should now comport well with the SMPTE standards which I believe is a centered rectangle 93% of the height/width for action and 90% for title. When in doubt, I'd suggest using the title safe area.

tl;dr the safe zones in the television world are 5% for action and 10% for titles.

In the TV production world, we have things called "Safe zones". These are areas that should not be covered up by TV overscan. For text and other important imagery, you can count on a margin of 10% around each side. So for a 640x480 image, you would deduct 64 columns from each side and 48 rows from the top and bottom.

So the title safe zone is 512x384, or 64x48 text cells.

For non-critical content, you can push this out to 5%, giving you a 576x432 action safe zone.

Those are the values I'd shoot for when designing a game for CRT displays.

Thanks everybody! If the VERA's NTSC output is being engineered to adhere to SMPTE standards, then that's what I'll adhere to.