Freeze frame/gonna drive me insane
September 11, 2019 12:03 PM   Subscribe

Can one extract a still frame from an analog videotape without using digital technology? Or are you stuck with taking photos of a monitor?

Here’s what confuses me: with film, you can snip out a rectangle that is a tiny photograph. Videotape on the other hand is opaque brown plastic. Videotape can still be edited by cutting and splicing, which involves finding frames ... in some sense. But can you pluck out just one frame?

Not only is videotape all mysterious and magnetic and brown, but each frame is split between two fields, at least in my crude, Wikipedia-based understanding of interlacing. Some formats (Type C, V2000) unite the two fields to create a freeze frame. But can that image be somehow fished out, carried around, printed on paper, etc.?

I do not plan to do so myself, but there are fictional characters who need to know whether it is possible. Please advise.
posted by sock_slink_slink to Technology (15 answers total) 2 users marked this as a favorite
 
The way vhs works is each frame (or if it’s interlaced half frame) is a diagonal stripe on the magnetic tape and a rotating read head scans across it as the tape advances. So if you just stop the tape moving you see the same thing over and over But I think the angle the head is spinning at anticipates the tape moving is why paused vhs video always looks all warbledy-doo
posted by aubilenon at 12:25 PM on September 11, 2019


I’m gonna say no, your characters* cannot extract a still frame from VHS and print it out without using a variety of digital instruments.

*Unless they are experts in analog computers, electrical engineering, reverse engineering, and have some decent source of accurate and technical knowledge on VHS encoding as well as some mechanical skills for hacking around with electromechanical tape machinery. In which case please send me your story :)
posted by SaltySalticid at 1:00 PM on September 11, 2019 [2 favorites]


I have not heard of anyone physically cutting together VHS tape — I think you may be thinking of physical film, where each frame is stored as an individual photographic image, and you can cut together an edit by physically cutting and tape-splicing (this is where the term “cut” comes from, in film editing. I think reel-to-reel audio, which uses similar analog magnetic encoding, can be physically spliced, so I guess it’s possible, but it seems like it would be really challenging to do accurately. Video editing is usually done with at least two linked decks, and usually an electronic controller that can control both. What I used to do in a tape edit was to set in/out points on a source tape, then use the controller to very precisely cue up and pre-roll the destination tape, to record that section of video into the edit. (My experience was mostly with S-VHS, but BetaSP worked the same way. Digibeta and other formats were similar but I never used them much).

But yeah, you can’t just cut out a single frame somehow. Pausing a VHS always looks wonky ( S-VHS and other higher-end formats worked better, but were more expensive and less widely available). I think there might have been a consumer device that could print a (poor) still image in the late 90s/early 00s, and I had at that time a cheap ($150 or so) parallel-port dongle that could digitize analog video at low-framerate 320x240 but that was digital, so maybe not relevant to your story.
posted by Alterscape at 1:09 PM on September 11, 2019 [1 favorite]


If you're talking about splicing video tape, that hasn't been done since the 1960s and isn't really feasible with modern helical-scan tapes. Maybe if the protagonist is into antique reel-to-reel machines?

The easiest way to get a freeze-frame copy would be to hit Pause on the source VCR and pipe the signal to another VCR where it would be recorded.
posted by RobotVoodooPower at 1:10 PM on September 11, 2019 [1 favorite]


To overly simplify, film works by having lots of little pictures on tape that moves rapidly. VHS works by having tape that moves relatively slowly past heads that rotate. The data is, as you noted, interlaced. Additionally, there's information in the control track that is needed to understand how to handle the information.

So, no, not really. It requires equipment to build a picture that a human would understand, whether its analog or digital.
posted by Candleman at 1:12 PM on September 11, 2019 [1 favorite]


Perhaps your characters could find a technologically brilliant electronics-whiz eccentric person who lives in some obscure filthy device-crammed pestilential space and somehow has *exactly* the tech they need (like say an old JVC VHS/MiniDV/DVD all-in-one deck and an old computer with firewire) so they can capture that frame in QuickTime and print it out on a vintage USB printer for which they brew their own inks?
posted by conscious matter at 2:04 PM on September 11, 2019 [1 favorite]


You can physically cut and splice video tape. You don't cut the ends square, though, you cut the tape parallel to the scan lines, IIRC. They used to make "splicing blocks" (sort of like a tiny mitre box) that assisted you in doing this with a razor knife. The cut ends were then assembled with special Mylar tape. It doesn't make for the cleanest edit, because of the interlacing, but before 3-deck editing systems became reasonably priced it was the low-budget way of editing video. (Think highschool A/V club, not something you'd do in a respectable TV studio.) Today it's generally done only to repair broken tapes.

Anyway... as to the original question of getting a single frame off of video tape, yes it's technically hard, but if the characters have access to even reasonably high-end video equipment from the 80s or 90s, you can handwave away the complexity.

This is all from (flawed) memory, but I believe the better editing decks—the ones with frame-by-frame jog/shuttle controls, basically—used multiple playback heads on the helical drum, such that when the tape was paused they could read both interlaced "halves" of a single frame. The result being, they could get a reasonably-clear freeze frame, and do frame-by-frame advance and stuff. Anything that was in motion usually ended up looking a bit blocky/torn, but stationary objects were pretty clear.

Anyway, so your intrepid characters could, with the aid of an editing deck, go through a tape frame-by-frame, similar to as though it were film. When they get to the frame they want, then you either need to just take a picture of the frozen image on the monitor (not to be sneezed at—with a tripod, you can get pretty good results this way), or there were some printers that took video input. They were rare, but someone doing video analysis might have had access to one.
posted by Kadin2048 at 2:10 PM on September 11, 2019 [5 favorites]


Digitizing VHS is a commonplace. Your characters can send the tape off and get a video file, then step through the file with VLC and hit the frame capture button.
posted by mpark at 2:36 PM on September 11, 2019 [1 favorite]


When I worked at a documentary production company around 2003-2006, we had a device that would plug into a video deck and print a black & white still image of the current frame. I don't remember what it was called or who the manufacturer was.
posted by Awkward Philip at 3:02 PM on September 11, 2019 [1 favorite]


Video graphic printers are available from Sony and Mitsubishi, but they are generally designed specifically for use with medical diagnostic equipment, such as ultrasound systems.
posted by Lanark at 3:07 PM on September 11, 2019 [2 favorites]


Are the fictional characters trying to capture individual frames, or remove them? They could capture them using a Snappy. But that wouldn't allow them to remove frames.
posted by wps98 at 3:11 PM on September 11, 2019


The Snappy is digital technology though.

There are a ton of ways to digitize videotapes and grab single frames, but the question stipulates they not involve digital technology. I remember reading about a device, back in the 1980s, that could print an image from a TV screen a la Blade Runner but I’m not sure it was an analog device and can’t find it on Google.
posted by Mothlight at 7:23 PM on September 11, 2019


I don't know how I missed the "without digital" part of the question! Please disregard my off-topic answer above.
posted by mpark at 9:55 PM on September 11, 2019


My "I could probably pull this off" thinking goes along Kadin2048's reasoning with a bunch of caveats. My main concern would be how precisely you could find the right places to cut the tape. How fast does the tape move vs 24fps and can you be that precise to cut between the frames. Film is easy, you have sprocket holes to align. There's no visual marker on the tape to align your cuts with.

There's also the interlace. If you have interlace frames 1,2,3,4 what are you cutting out? A single half-height frame 1 or 2 or 3? Or which do you pick? 1,2 or 2,3, or 3,4?

Once you've spliced the original back after removing your frame, how do you use it? Splice it back into another tape and do the same freeze-frame and jog to find it? Create a fake VHS tape that just holds the frame stationary in the right place (so the VCR thinks it's playing normally but only seeing the same bit over and over).

Printing a B&W picture is relatively easy. It's just the luminance channel. The same way color video is backwards compatible with B&W video. You could probably do the same with other channels and do a really weird like color print process and keep it analog.

They also used to make special hoods that attached to your monitor and held a camera steady (and blocked out extra light) just for photographing video screens.

So, hard, but probably doable if you try hard enough.
posted by zengargoyle at 2:41 AM on September 12, 2019


It would help to know what era or even what year your fictional characters occupy, because the historical overlap between availability of analog videotape and the availability of digital technology is quite wide; there will certainly be years in which the need to avoid specifically digital solutions will require additional fictional rationalizations.

There were certainly pre-digital devices for transferring analog video to film, and there's no reason why you couldn't feed one of these from a video tape and then cut out a single frame from the resulting film or have prints made from it.
posted by flabdablet at 7:32 AM on September 12, 2019


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