problem on captured VHS frames

[stefangs]

hi,

i'm hoping someone can shed some light on this problem. i'm digitizing a bunch of VHS tapes and all files end up with a border. top, left, and right don't bother me so much as they are just dark (not quite black), but the bottom looks like a mumble jumble of the frame itself squished across a few pixels which i find quite distracting (see attached frame). this happens on both PAL and NTSC tapes.

any idea where that comes from and what to do? it's not problem for my editor (final cut pro) to crop that, but then i would probably disturb the frame size when i render out, so i'm not sure if that's a good idea.

thanks for any insights,
stefan

[jagabo]

All of that is normal. The junk at the bottom is head switching noise. You always get that with VHS tape. The black borders at the left and right are there because the card captures a picture wider than the normal broadcast signal to assure the entire picture is captured even if the signal is slightly off center. You don't see those features on TV because TV's overscan the image. Ie, they are covered by the bezel on the TV.

The only thing you should do is cover them with solid black, especially the head switching noise . So they don't eat up bitrate on the DVD.

[DB83]

How did you capture that image ? Surley it should be 720*576 pixels ?

Other than jagabo's suggestion, if you consider cropping the image to remove either the vertical black and/or the horizontal noise you may well have to de-interlace the video first else you could destroy the video completely.

Best to leave alone and let the tv overscan take care of it.

[robjv1]

Yup, as everyone else mentioned -- there is nothing wrong with your equipment or capturing process, the head switching noise is totally normal.

Definitely do not crop your footage to get rid of the uneven black bars or head switching noise at the bottom. You should use only potentially non-destructive practices to deal with it.

If you plan to watch it on a TV, you are unlikely to see any of it, as it will more than likely fall within your televisions overscan area. Some TVs will let you adjust the amount of this area too, in case your TV does show it. Check your users manual.

If you're planning on watching on computer monitor in full screen mode, the noise will show up, as monitors don't have an overscan. Some programs (like VLC Player) will allow you to generate a custom mask in real-time on playback, which is the best of both worlds -- you don't have to re-encode your footage and you can enjoy it a computer minus the bars/noise.

If that isn't our preference, mask it in software (i.e. cover the offending areas with a solid black border). You can do it easily in VirtualDub (Mpeg2/Mod) with the 'Fill' filter. Note that will still require a re-encode (i.e. you'll lose some quality, how much depends on the methods and encoder you use).

Another way to handle it is to create a mask using a subtitle, which I thought was pretty clever and cool, as you don't have to re-encode the footage:
https://forum.videohelp.com/threads/343940-Resolved-Use-Subtitle-to-Create-Border-on-DV...ut-Re-encoding

There are many ways to skin a can, as they say!

[stefangs]

wow... thanks to everyone for a truckload of insight and advice. i guess i will go with a small black border then - i'm sure final cut pro has a plugin that can do that.

recompressing should not be a big deal, as i capture in apple ProRes which is pretty good and then keep important footage in that format. less important stuff i'll probably render in H.264.

just out of curiosity - i'm saving my footage interlaced just because it's closer to the original. do you guys save your footage de-interlaced?

stefan

[DB83]

Apple ProRes. What codec is that ?

VHS source is interlaced. De-interlace and you re-encode = loose quality. Keep as interlaced.

[jagabo]

http://en.wikipedia.org/wiki/ProRes_422

[jagabo]

i'm saving my footage interlaced just because it's closer to the original.

That's your best bet for archival storage. Deinterlacing always results in some loss of quality. Although the best software deinterlacers (you won't find them in FCP) are currently better than the typical TV deinterlacer, if you deinterlace before archiving you will forever lock the sofware's insufficiencies into you video. It's possible TVs will get better in the future so an interlaced archive might eventually look better on a TV.

It's ok to make a separate deinterlaced copy for viewing now. Or for uploading to YouTube or to someone else who doesn't know how to handle interlaced video.

[stefangs]

Apple ProRes. What codec is that ?

VHS source is interlaced. De-interlace and you re-encode = loose quality. Keep as interlaced.

ProRes is a codec made by apple for editing in high quality. there are a few flavours, the are all compressed (intra frame), but compared to VHS quality, you could call that transparent. it's also the codec of choice when working with final cut pro (apple's video editor).

yes, i agree with keeping interlaced. interestingly, when i set up the video grabber, i checked the 'interlace' option, because i'm digitizing interlaced material, right? no, beause it looks like it interlaces the material over again (will look squished, because it loses half the vertical resolution) - so unchecking the interlace option is actually what i want.

stefan

[stefangs]

if you deinterlace before archiving you will forever lock the sofware's insufficiencies into you video. It's possible TVs will get better in the future so an interlaced archive might eventually look better on a TV.

It's ok to make a separate deinterlaced copy for viewing now. Or for uploading to YouTube or to someone else who doesn't know how to handle interlaced video.

yes, that's my thinking, too. besides, storage is so cheap now, that i don't mind having stuff two ways.

stefan

[DB83]

But surely if you un-check that interlace option you will end up with progressive ie non-interlaced video (unless the option has reverse logic) and that is exactly what you do NOT want.

VHS is normally captured interlaced top-field first.

[stefangs]

But surely if you un-check that interlace option you will end up with progressive ie non-interlaced video (unless the option has reverse logic) and that is exactly what you do NOT want.

VHS is normally captured interlaced top-field first.

yes, i think it is reverse logic. that's why i was confused. how else would i end up with a video at half the vertical resolution? i also see the combing effect in my editor when the interlace option was *not* checked.

but before i finalize the workflow and do everything the same way, i should probably check the material on a few screens (tube tv, flat screen tv, and computer) to make sure everything gives me a playable and acceptable result.

stefan

[DB83]

Well I believe there is also a mediainfo tool available for Mac systems. With that you can check the parameters of your capture.

I thought that half vertical resolution was the result of field discardation and not interlacing.

[stefangs]

Well I believe there is also a mediainfo tool available for Mac systems. With that you can check the parameters of your capture.

I thought that half vertical resolution was the result of field discardation and not interlacing.

that's a very useful tool, thanks for the link.

i think you have a point here... perhaps my own logic was reversed . my quicktime player plays the video normally, no matter if i record interlaced or not, but my editor does not. the footage with interlace option checked plays back at half the height, only in pause mode will the screen be stretched to normal size. now that i think of it, that behaviour is to be expected, but i was confused, because the QT player plays it at normal size no matter what.

so i presume the editor, having a progressive timeline, plays only the top field, disregards, the bottom field, making the image shrink in size, but upon pause looks at both fields and displays that. i see if i can find something in the manual that confirms that.

stefan