Discussion

BobMcBob: Tech Tangents is one of the best retro channels on youtube but by retro I dont mean glorified nostalgia either. Shelby puts a lot of work into his videos and likes to showcase what awesome engineering went into some of the early tech that was practically magic. Love the channel and glad to see it on HN.

bcraven: I must admit I am finding his choice of facial hair design extremely distracting.

Nux: Rocker with a hint of taliban? \m/

VorpalWay: The live stream of this had more interesting things as well, such as looking at the ink on mimeographs compared to inkjet printing. Long and rambly as live streams tend to be, but it is there if anyone cares.https://m.youtube.com/watch?v=zIsCswtkozI (mimeograph around 3:36:00 mark)

smusamashah: So CAV (constant angular velocity) is an encoding format for laser disks. When something is written with CAV, it is basically analogue data and therefore repeating patterns can be recognized on the disk.

jmkd: Not simply repeating patterns, readable text from the credits as shown in the video.

accrual: Here's where the text comes into focus, pretty cool:https://youtu.be/qZuR-772cks?t=1540

amelius: But the opto mechanical parts of a laserdisc reader are way more interesting than a microscope.

wtallis: No, CAV has nothing to do with encoding, and both analog and digital formats have used both CAV and CLV and hybrids of the two.The legible text seen in the microscope images happens because of the combination of LaserDisc recording a raw and uncompressed encoding of the analog video signal, the way that LaserDisc used CAV to store an integer number of frames per track so that the image data for corresponding on-screen locations of subsequent frames would be aligned at the same radial position on the disc, and the credits scrolling vertically at constant speed.If LaserDisc had used a digital encoding (especially a compressed encoding), the data on disc may still have had discernible patterns but the text would not necessarily have been legible. If it had used CAV but not stored a whole number of frames per track, then temporal and spatial locality on screen would not have corresponded so well to spatial locality on disc. And the vertically-scrolling credits are pretty much the only kind of content that can produce the recognizable and legible images on the disc surface.I think the fact that the aspect ratio of the text came out approximately right probably is a consequence of the scrolling speed of the credits being chosen to suit the vertical resolution of the video. If the text had appeared squished in the microscope, it would probably have been moving too fast on screen to be clearly legible.

rustyhancock: Here's a screen capture of the end credits visible on the disc the videos worth it but I do think sometimes you need to start with the money shot https://ibb.co/v4KK88fF

crazydoggers: This is from a CED not a laserdisc.

ralferoo: Actually amazing being able to read the text like that, and on two different types of discs. Great video, was much better than I was expecting it to be from the title!

xattt: Is the image seen via microscope basically a readout of the image on a spectroscope?Those can have near-legible images, but most of the time they are not.

csours: Not nearly as cool, but I was able to show a colleague the letters in a raster image section of a pdf using xxd by varying the output width

oofbey: Fun fact about laser discs. They are analogue not digital. CD’s store digital information with the presence or absence of pits. Fairly ancient but still fundamentally feels like a very old version of a thumb drive.Laser discs are not digital. They encode the analogue video signal’s value as the length of the pit. It is digitized in the time domain - sampled at some frequency, but the “vertical” signal value is stored entirely analogue. In terms of encoding it’s more similar to a VHS tape than a CD. Kinda crazy.

EvanAnderson: I wrote a simple tool, when I was a kid, that dumped binaries into VGA mode 0x13 and allowed me to vary the width. Mode 0x13 is one byte per pixel so it was just a simple REP MOVSB to put data into the buffer (no worrying about bitplanes). It was so useful in reverse engineering software. Besides raster data, regular data structures often jump out.

a-dub: yeah i remember learning this as a kid and being surprised. i originally thought laserdiscs were modern high tech, but then they turned out to actually be from the late 70s/early 80s with the primitive analog video encoding where red book audio cds of the mid to late 80s were actually digital.

mh-: I just learned this in my 40s and am surprised. Very cool.

Retr0id: Fun fact, if you load a file with extension ".data" into GIMP there's a UI where you can set the pixel format and adjust the width/height with sliders

VerifiedReports: No; it's strictly a reference to constant RPM or variable RPM.CAV discs contained one frame per rotation. While this meant you could only fit half an hour on one side of a disc, it did give you perfect slow-motion and freeze-frames.I worked in a video store and loved LaserDiscs. The Duran Duran video album was CAV, and the Pioneer LD-700 had such a fast transport mechanism and remote control that I could to DJ-style "scratching" with it.

macshome: That’s not a LaserDisc, it’s a CED video disk. Totally different technology.

ZeWaka: A LaserDisc was featured in the video alongside the CED video disk.

userbinator: Photoshop does the same with the .raw extension.

onnimonni: I'm not that familiar with CED but the fact that we can see the images with microscopes is because these are analog discs? And that was because computing power back then was non-existent so they didn't use any kind of compression?

iamtedd: If you watch the video, he looked at both.

CamelCaseCondo: I did the same thing to evaluate random number generators by drawing pixels with the count value. You see a pattern, line or clusters? Bad generator.