Hey guys,

on most SDI + processor setups I've seen the DVD players "failed" the basic cropping testscreens on various test DVDs. On my Sony DVD player for example the lower 2 or 3 lines are missing. On a friend's Denon 3910 some lines are missing from the bottom and the right. While it doesn't really bother me, I'm wondering what actually happens to the signal.

I guess the SDI "carrier" signal is always 480 lines (576 on PAL). What happens when I see a picture, that's missing - let's say 3 lines - on the bottom. How are the remaining 477 lines mapped onto the 480 signal of the SDI signal ?

As I understand most DVDs players have some kind of overscan / cropping on all the outputs available.

What's the general consens on this ?

Greetings
Tobias

Tobias, if the SDI signal is properly centered there should be no loss of the image to overscan

there are however some players that do have slight cropping issues, being this comes from the mpeg decoder in many cases the SDI output is affected

-Gary

nothing new so far. Given that the MPEG2 decoder does some kind of cropping - the question remains: what happens to the signal ? how is it possible that e.g. 477 lines are recognized as 480 lines by the processor and are perfectly aligned top to bottom at 0% overscan setting (on the display and the videoprocessor).

I'd assume that the "lost" pixels are just replaced by black, so the signal is still complete.

I remember the picture reaching down to the very bottom and still showing a 2-3 line crop on the test picture, but I'll recheck to be sure.

I'd assume that the "lost" pixels are just replaced by black, so the signal is still complete.

That is exactly what happens. The 480 scan lines are dictated by the timing framework in which the SDI stream is made from. If the image comes up short, then you have to pad with back - or some data value.

I have seen some pro gear actually pad the half line with random data which shows up pink or green.

...I guess the SDI "carrier" signal is always 480 lines (576 on PAL)....

The SMPTE standard (SMPTE 259M) resolution for 525 line interlaced format is 720 x 483. ITU-R BT.601-5 shows 720 x 485 resolution for 480P/59.94.

...How are the remaining 477 lines mapped onto the 480 signal of the SDI signal?...

What you are actually looking at is 1080 lines (or at least I am), which is not an integral multiple of 480, 483 or 485 lines. So interpolation necessarily occurs at the video processor and I suppose it is just as easy to interpolate up 477 lines to fill the frame as it is to interpolate up 483 lines, or however many lines you actually have.

Thanks guys! I re-checked using the Avia overscan pattern and you were right about the masking. Looks like two lines at the bottom are blacked out and in addition the whole signal is shifted 1 line down plus one line to the right.