Old NTSC tricks: 240p?

John Foust <jfoust at threedee.com> writes: There's a pretty good description here, with diagrams of the video waveforms involved for both PAL and NTSC (both use the same idea): http://martin.hinner.info/vga/pal.html In brief: a video signal consists of a series of fields (about 60 per second for NTSC). Each video field starts with a series of "vertical sync" pulses that returns the electron beam to the top of the screen (there's also a "horizontal sync" pulse at the end of each line, which moves the beam back to the left of the screen). There are different vertical sync pulse sequences for odd and even fields, so the monitor knows to offset the even field by half a line. A normal video signal alternates between odd and even fields; in the kind of non-interlaced signal you're talking about, every frame starts with the odd field vertical sync, so the monitor always pulls the electron beam back to the same place. Cheers, -- Adam Sampson <ats at offog.org> <http://offog.org/>