[FFmpeg-user] How can I transcode a video to 800x480, non-square pixels?

[John Klimek]

I've purchased a car stereo that lists the following dimensions:

6.95 in diagonal (156.6 mm x 81.6 mm)
800x480, 16:9 aspect ratio

If the pixels were square, that would be 15:9 but the physical dimensions
are definitely 16:9.

If I have a video encoded at 720p or 1080p and I want to convert it to use
the entire 800x480 display and the non-square (?) pixels, how can I do this
with FFmpeg?