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View Full Version : capturing PAL - overscan and frame-size question


nig103
2nd June 2004, 17:55
hi,

Recently I've been capturing video and TV to burn to DVD. Thanks to these forums and the guides here at Doom9, (and probably most of all the sourceforge bt8x8 drivers!)(I can never quite get how companies can get he hardware right, but not the software, the standard drivers with my card hardly worked at all!) I've been able to create some great quality captures. I've tested alot of stuff and am very happy with the results, I'd actually be really interested to see what a standalone DVD recorder can do as I don't see how it can get much better! So I'd like to extend a big thank-you to all the authors of these brilliant programs we all use and to doom9 for keeping this great resource up and running.

Anyway, some details about how I'm capturing...
Using VirtualVCR, capturing to 720 x 576 PAL, huffyuv codec
Then writing an avisynth script which -
corrects audio sync
crops to 704 x 576
seperates the fields and runs some noise reduction
corrects the color ranges
and then am loading that into CCE 2.66sp to encode to MPEG-2

My final hurdle on the testing front is overscan. Basically I'm capturing to watch on the PC, TV and a CRT Projector. So from what I understand about overscan and from some tests I've done, the TV doesn't display the whole picture anyway. It cuts off about 16 pixels it seems around the edges. My picture I get from my cable provider comes through to the capture card pretty much full-frame apart from about 16 pixels of blackness on the right-hand side.

Whereas my CRT projector actually displays the normal TV image pretty much exactly the same as the Video-capture card sees it. No overscan. You get the black bar down the right hand side of the image that is about 16 pixels wide.

Anyway, so at the moment I'm capturing at 720 x 576 and cropping to 704 x 576 (sometimes I maybe crop a little more and add black borders for what I've cropped to get rid of a funny grey line I get at the bottom of the image etc...)
Now this 704 x 576 DVD plays back really well on the projector but on the TV the overscan differs slightly from the way normal TV gets displayed. my DVD version seems to cut of a bit more on the right hand side than normal TV does and the DVD also seems to display more lines vertically. Tomorrow I'm going to bring home a digital camera from work and take some photos of the TV screen whilst capturing it so I can compare the normal overscan the TV does to the overscan it does when I playback my DVD on the TV. I just thought I'd throw this one up in the air to see if anyone else had dealt with it before.

Basically, I've done a bit of reading on it and it seems as though alot of people seem to add the 16 pixel borders on every side to get the whole picture displaying on the TV. Seeing as I want to view on the PC and the CRT projector as well, I don't really want to do this as I'd then not be using the whole screen on my projector. So I'm happy to lose some of the picture whilst watching on the TV, however I'd like to make what I lose the same as what I'd normally lose if just watching stuff on TV.

Oh I've done some quick test of a 720 x 576 res versus a 704 x 576 res to see if it gets more of the right hand side of the picture onto the TV but its exactly the smae as 720 on the TV.

So my question is, what would be the best resolution to capture at so that when played back on the TV I lose the same edges of the picture that I'd normally lose watching TV, that will also keep the video pretty much full frame for watching on the CRT projector and the PC?

I've read in a few posts that some people capture at 712 x 576 and then pad to 720 x 576, maybe this will get me my inch or so of right hand side back..... I will grab a camera and takes some shots tomorrow night which can maybe explain my question a little better, but in the meantime any info on the subject is much appreciated.

Thanks :)

trevlac
2nd June 2004, 21:12
Your post was quite long ... :)

Some things to know.

- A PAL picture is 702 (DVD Pixels) wide
- Your card/driver captures 704 Pixels where the PAL picture is centered
- Your card/driver captures 704 Pixels regardless of what you ask
- If you ask for 720, it caps 704 and resizes to 720



So .... You should probably cap at 704. You could then crop in a little and pad black out to 704, if you have unsightly borders. :)

nig103
4th June 2004, 07:25
Thanks heaps Trevlac,

It was a long post wasn't it! Sorry about that it was very very late when I wrote it and I was trying to make as much sense as possible (which obviously required alot of ranting at that time of night!)

704 x 576 worked very well. I also moved the picture down 6 pixels and to the right 2 pixels when cropping and padding back to the same res to get it as close to how the TV signal is broadcast on the TV. I took some shots with a Dig Cam of the broadcast picture on the TV versus the DVD picture on the TV and they are now basically exactly the same, (losing the same areas to overscan). Woohoo! I must admit I didn't read that much about whether your card resizes or not in the guides when I probably should have. It's actually pretty silly as I did so much reading on everything else except that. So thanks again for saving me alot of time, finally after 4 weeks of playing around I have a really good standard to capture to.

Thanks Mate
:)