White single-frame flashes VHS capture

[gamjerr]

Hi all,

See these screens http://imgur.com/a/Jj6XC

Any idea if this is just VHS degradation or some other problem? I've heard of macro-vision causing flashes, but have no idea what those look like. These tapes are from 1994. I have about 100 tapes from similar time frame and I've had this issue on a few. Note this specific set came as 2 tapes and I am only having this issue on one of the tapes and it is throughout the entire 4.5 hr tape - it does vary in frequency. Also I'm capturing via virtualdub - can anyone think of any filters or another method to remove/soften the flashes post capture? Thanks in advance.

[Brad]

It's actually a single field, in this case. Oddly, the horizontal bands look regularly-spaced in an alternating pattern.



Top ~1/3 of field good, middle >1/3 alternating bright with more-bright, bottom ~1/3 brightened.

If you capture the same segment again, does it appear on the exact same fields? What about playback to a TV?

You're not going to be able to remove them post-capture unless you can lower the Contrast proc amp control a lot because so much of the frame is clipped to pure white.

[jagabo]

Yes, the other field doesn't show the problem. The two fields stacked instead of interleaved:


[Attachment 41431 - Click to enlarge]

If the problem happens on different fields each time you capture the tape, and it's not too frequent, you can use a median-of-3 (or 5. etc.) filter to eliminate the bright fields.

If the problem doesn't happen on multiple consecutive fields, and it's always the same general area that's very bright, you can probably eliminate them with a smart replacement with motion interpolated fields.

You should upload a video sample to this site.

[gamjerr]

Thank you both so much for trying to help me out. I ran the tape through again and the flashes are at different spots in the tape. Attached is a uncompressed brief sample (93MB). I'll look into a median filter - any recommendation on that front would also be appreciated. If it is helpful info, currently my setup is Mitsubishi HS-U448 > Diamond VC500 -> virtualdub avi (huffy)

[LMotlow]

This is bad tape that doesn't track well, a lot of dot crawl, and sending your capture card false Macrovision signals because of bad tracking. You need an external frame-level tbc.

[gamjerr]

Do you think this something a DVD pass through setup could fix? It seems like choices on standalone tbcs are a bit limited.

[LMotlow]

Copy protected tape disturbances come in many flavors, and multiple versions of Macrovision. In my own case I encountered one such tape, a home recorded job and certainly not retail, that had frame flashes. My ES10 pass-thru didn't solve the problem, yet my old AVT-8710 (green version) did the trick. But I've seen recent threads where an ES10 or ES15 pass-thru fixed the false detection issue. The flashing screen you posted doesn't look like the same Macrovision I encountered (white flagging on top borders, which is more typical of genuine Macrovision) so I'll make an educated guess and say that a pass-thru will probably work here, since they worked elsewhere on similar signal errors.

I don't know why your sample had such obvious dot crawl. Are you using s-video connections?

[jagabo]

In my experience the ES15 cleans up the signal of non-Macrovision protected tapes enough to prevent false triggering of the overzealous Macrovision detectors on many capture devices. It does not remove real Macrovision.

https://www.youtube.com/watch?v=0XLGFU__0Wk

Real Macrovision usually causes capture devices to distort the picture far more than in the sample in post #4.

[lordsmurf]

That looks like Macrovision, and an external TBC made for VHS is required.

[Brad]

That looks like Macrovision, and an external TBC made for VHS is required.

It appears to be some semi-professional lecture recording, described as a 4.5 hr tape in a set of 2 tapes with only this 1 tape causing problems. Even if this was sold, there's no way they licensed Macrovision. (Was there ever any release so cheap that it used EP yet ponied up the cash for MV?)

DVD passthrough is a good idea regardless, as the frame is wiggling and the horizontal position varies so much from line to line that the black borders are angled. This is typical when the VC500 is fed unstabilized videotape, and you can see the same thing with the Hauppauge USB-Live2 here. They both use a "Conexant Polaris" video decoder.

[gamjerr]

Yes these were commercial tapes, but again this specific set came with a second tape and that one played perfectly fine. I have about 30-40 of these sets and I've seen this specific issue maybe less than 5 times. I do think on average the tapes where I've seen this also have a lot more jitter, so I think the explanation makes sense. I'll look around on ebay for one of the panasonic models or the AVT-8710. Sounds like I should have invested in a tbc or dvd pass through option a long time ago. Thanks again to everyone for the help. What a great community!

[Brad]

The AVT-8710 will do a worse job correcting the horizontal jitter than even a mediocre DVD passthrough.

[jagabo]

In case you can't get rid of the bright flashes with a TBC, here's some AviSynth code that helps. It replaces the bright flashes with a copy of the previous frame (field, really).

function ReplaceFlash(clip v, clip alt)
{
  testclip = v.mt_binarize(220).mt_inpand().mt_inpand().GreyScale()
  ConditionalFilter(testclip, v, alt.Subtitle("sub"), "AverageLuma()", "lessthan", "10")
}

AviSource("test.avi") 
AssumeTFF()
ConvertToYV12(interlaced=true)
QTGMC(preset="fast")
ReplaceFlash(last, last.Loop(2,0,0))
ReplaceFlash(last, last.Loop(2,0,0))

This leaves frames with only slightly lighter bands. You could try playing with the mt_binarize() and value to catch those too. And you could try removing frames with dark flashes with a similar technique. Oh, the code stamps the substituted frames with "sub" in the top left corner to make them more obvious. Remove the Subtitle() filter to get rid if that.

The original on the left (bobbed with QTGMC()), cleaned on the right:

[gamjerr]

Just wanted to say thanks again to everyone. This issue appears to be fixed by simply using a ES15 as pass-through. Reduced horiz jitters as well. Thanks for the suggestions. Now to do more research on encoding.