Capturing from a degraded source?

[TurboCMinus]

Any tips for doing this? (Marvel G400, Win98FE). I have a tape I'd like to get some clips from, it's a bit degraded, one thing I tried was to actually pause the VCR and then screen-capture every individual frame, like 3 times for each frame. Usually there was always one frame that was pretty decent that I could keep, BUT, it shakes a LOT vertically and cuts off the top and bottom sometimes. I took the screen caps into Paintbrush and adjusted their vertical location, using something in the shot as a reference. Then fed the thing into an AVI creator. It worked to an extent, but it really is a mess not to mention the top and bottom of the video cuts out in parts.

If I try to cap normally it drops a lot of frames. Also, the source tape is basically a collection of short clips of things one after another, and I think that is causing problems too - the synchronization signal (??) being out of sync when it goes from clip to clip. I dunno how that works exactly. Advice appreciated.

[landrover]

What resolution are you trying to capture? When capturing degraded footage you shouldn´t put too much strain on the system. I borrowed a 10 or 12 year old VHS tape with a television broadcast of "Nosferatu" and managed to get a decent VCD from it, because every drop-out on the tape was skipped by the Marvel. That dropping of bad frames has it´s advantages: you won´t see them back in the captured file. The Nosferatu VCD was far better watchable than the VHS tape.

landrover

[jeff b]

Given a system that's capable of capturing good video without frame drops, it's worth having some outboard video processing gear such as genlock, color corrector, etc. for exactly this situation. These various pieces of otherwise extravagant equipment end up in your arsenal sooner or later because they are the only things that will work for certain situations.

In this case, it would be the genlock that I'd try, and possibly a couple of different VCR's.

Jeff B

[davpen]

How would you use a Genlock to fix this sort of problem? Wouldn't a TBC be the most appropriate tool?


David.

[TurboCMinus]

jeff: What exactly is genlock? It helps the frames to "lock in" properly? Sounds interesting for whenever I have any money.

landrover: I guess I'd take either full-res or half-res. I'm not certain, but it SEEMS like maybe it actually succeeds in getting more frames when it does full res?? Seems weird. Anyway, I know all the frames ARE THERE on the tape, because when I paused my VCR, went frame by frame (its frame by frame isn't even that amazing, just OK), and screen-capped each frame that way, I WAS able to get EVERY frame, although a few didn't look great, but I was able to manually adjust/move/fix those to some degree. It's just a question of the capture hardware/software being able to successfully recognize and capture the frames while it is playing.

Another factor is that this is a PAL tape someone sent me, and I am using my multi-system VCR to capture it. I can only watch it on my cap card and it's the ony VCR I have that can play the tape. So, limited options there. If I got a "genlock" would I have to get a PAL-only version? That would suck.

I've attached one frame of the captured file to show some of the various things it does, note the messed up top of it. (also is full screen and interlaced but that's beside the point.) Usually when I was capturing individual frames (picture screen cap), for the "bad frames" I would get 2 that were like this and then 1 good one that I could keep. That's why I know the good one is in there, its just a question of getting it off the tape.

[TurboCMinus]

Follow-up question: When it "drops frames", what exactly is it doing? Meaning, in the captured file? Is there any program out there that can tell me exactly WHERE all the dropped frames are? I have tried inching through in VDub, and I see that some frames next to each other are identical. Those are probably the ones that are dropped, but that could be due to other reasons too. Be nice to know for sure. The reason being, if I could get most of them captured normally, and then find out where ALL the dropped frames are, and then grab those manually with screen capture and insert those somehow. That would be superb. But somehow I doubt there is anything out there to let me do that easily. I'll probably have to first save the entire AVI as some kind of BMP sequence, manually insert the pics in the sequence and rename everything or god knows what and then re-assemble it as an AVI. :P

[jeff b]

Dave, you're right... I'm getting old and feeble minded. The appropriate tool here would be a "TBC" (Time Base Corrector), and in this case would have to be able to run PAL.

The trouble with VCR's is that the time base can come out of the box uneven, and not "perfrect". This is usually a situation that never causes a problem for a TV set, since both the VCR and the TV are analog based devices. The problem with capturing the analog video out of the VCR to a digital file on the computer is that the digital capture hardware and software wants a "perfect" time base to work with. Once that time base varies up and down beyond a certain point from "perfect", the digital side of things can start getting fouled up.

During one second, it gets exactly 25 interlaced images, then during the next second it gets exaclty 24, then during the next second it has to decide how to handle 26 or 27 images, and so forth. This is not a problem for a TV set, but it sure is for desktop video capture!

What the TBC unit will do is re-process the analog input and spit it back out to a "perfect" 25 frames per second for you.

Jeff B

[TurboCMinus]

Looks like they're about $170 or so. Hmm. Maybe someday... another interesting thing is I see that they also remove macrovision.

[landrover]

Yes, a TBC would in most cases do the trick. Although I´ve seen TBC´s outputting footage even worse than it got in.
But I took a look at your frame and wonder if you have nothing more than a tracking problem....

[TurboCMinus]

It's possible some tracking adjustment would make it better, but I think one problem may be that it is actually a COPY of someone else's degraded tape, and the tracking problems may have been on the source. I don't really know how that works exactly or if a tracking problem on the source can be fixed AT ALL now with the destination tape. One thing I am trying now is, using Virtualdub, for short clips I am writing down every frame that is dropped or bad, then capping it several more times, and a lot of the time the frames which were missing or bad before come out in the next captures. So I am just gonna save it as a BMP image sequence and try to splice it together that way. :|

[landrover]

Sorry to disappoint you, but you can't restore tracking faults from an earlier source. Technically it means that on your current tape the degraded tracking result has been tranferred into the new video track, of which the tracking could be flawless.

[TurboCMinus]

Well, I am pretty sure it's a combination. Because with 3 different captures I can get 3 different sets of dropped frames. One good thing this did is got me to look more into the whole interlacing thing, and what I am doing now is capturing full-screen full-framerate, using the unpack deinterlace method and I'm gonna edit it all manually until I have every single 50 FPS PAL HALF frame. Then I'm gonna try making an actual 50 FPS AVI. Not sure if my machine can handle that though. We'll see.