Junk at Top and Bottom Edges of Capture?

[quicksilverg4]

This is probably a very basic analog capture question. I'm using Mac hardware so it might be unfamiliar to PC users, but if you need more info on it just ask.

I'm seeing things like white lines at the very top and bottom edges of my captures. I've always seen this when playing with the built-in capture hardware on older Macs and figured it was due to not so great hardware. Now that I'm trying to learn more about capturing video so that I get better results its dawned on me that what I'm seeing might be on the original VHS tapes but located in the overscan area that doesn't show when they're played on a TV.

Does this sound correct or am I having problems that need fixed?

Source: Panasonic AG-1970 playing commercial VHS
System: Dual G4 1.25 GHz
Capture Card: Aurora IgniterX
Capture Software: MediaGrabX (very basic capture app from Aurora)
Capture Resolution: 720x480
Compression: Either MJPEG-A or uncompressed

[yoda313]

Yes most likely thats the overscan portion. What you see on your computer isn't exactly what you see on the tv. When you burn the dvd and play it on your regular tv you shouldn't see those faint lines.

Now if its a tracking line thats a different story. You'd need a svhs vcr with a tbc to stabilize the image to correct the bad video image.

[jimmalenko]

Yes most likely thats the overscan portion. What you see on your computer isn't exactly what you see on the tv. When you burn the dvd and play it on your regular tv you shouldn't see those faint lines.

... on CRT TVs, that is. They will still show on LCD TVs.

[edDV]

Junk at top is vertical interval test signals and data including closed captions. Botton usually is clean for broadcast but often has head switch junk when playing VHS, Hi8 or 8mm

[quicksilverg4]

Thanks. After paging through the forum some more I came across some similar posts that confirmed my thinking.

So let me make sure I understand the fix to this. I need to crop this stuff out of the file during encoding right? So I'll end up with a file that's not exactly 720x480. Will this cause problems? I had a look at some Divx files I have that were made from DVD rips and they have resolutions of: 640x272, 576x240, and 592x320. Why so many variations?

And is there no way to eliminate this problem during capture? Because my card captures in MJPEG or uncompressed I'll be reencoding to something a bit more suitable after capture so a crop during that stage is ok. But if I capture in MPEG2 using my Wired Mediapress card then I don't want to have to reencode afterwards.

What I'm trying to do is move a bunch of my movies from either VHS or DVD to a format (probably MPEG2 or Divx) that I can keep on my computer and either watch there or send out to the TV.

[jagabo]

Divx can be pretty much any frame size. DVD must conform to the DVD spec. You should mask the noise (leaving the frame size intact), not crop it.

[edDV]

You'll never see this on a CRT TV. Even LCD and Plasma TV's don't show the outer 5-10% of the image. All this is known as TV overscan.

If you crop the file, you will loose quality when it is rezoomed (scaled) for TV display, plus you will loose more from the sides top and bottom.

If you don't want to see this stuff on the computer, mask it with a frame rather than cropping. This keeps the central pixels unscaled.