So does anyone know the encoding scheme of a laserdisc? Everyone seems to say composite, which is true, but that's after FM has been demodulated and doesn't say anything about the low level scheme on the disc itself. If it's a demodulated radio frequency, it should be using some sort of standardized pattern. How else could so many laserdiscs be understood by a single player? I know digital audio tracks on LD use EFM (eight to fourteen modulation), but AC3 for example is decoded from an analog RF signal (on right stereo analog audio channel) which is completely different. I'm guessing laserdisc video uses something similar to AC3 RF, but I have no idea what.

It's FM as you described. Just like FM radio, just a different bandwidth. Philips invented this in the 60`s or earlier. Later came CD and pcm and it was added in the 80's. With the pcm added now you can have lead-in with data to jump tracks. The digital stereo sound is 16 bit just like CD. There are just different unused bands analog audio and digital are stored in the FM modulated signal.

Yes, we do know.
This question gets asked ever so often on here, & a search will turn up repeated answers of different detail. If you really want to get into it, PM me your e-mail address & I will send you numerous MB of technical papers on the subject.

Yeah, sorta common, this question.

Only someone who didn't live through the analog era would ask this. I'm not trying to be insulting, but it's true.

There is only one laser, and therefore one main signal. Everything is crammed into that waveform. Everything is done in real time with no digital cache, video RAM, etc.

If you learn how things like FM radio work, you'll understand to his. How does a stereo LP fit two (or four) channels into a single groove read by a single needle? How does one line of cable from Comcast manage to carry internet, digital TV, and analog TV on one wire? When you understand these things you'll know how LD works.

Pioneer Tuning Fork #6 has a good overview of the entire system (as of the early 80's), and I think #8 details digital audio. Those are up on another forum, should be easy to google another copy.

Interesting tidbit: Cat 7A and 8 RJ-45 cables will have enough bandwidth to carry cable TV (at least over short distances)

That's not entirely true. No LD player ever provided a picture still pause for a CLV disc without using some form of digital memory. You only get a picture visible during pause if you are playing a CAV disc which requires no memory or a CLV disc with a digital memory facility.

Thanks for that Happycube! Lots of information on that document.

From what I understand, the pits and lands on the disc create pulses, which in turn create squarewaves, which sounds like PWM. I guess it's safe to assume the pits and lands on LD are literally the composite video along with the multiplexed audio (with the exception of audio being converted from analog to binary EFM on newer LDs). If bluray was used with something like this, we could probably have something like 4K definition video possible (or something close to that).

I've heard mention that Super Audio CD (DSD audio) is a format similar to LD. I wonder how many other formats work like LD? Sounds to me like optical media is a futurist record player advancement of some sort (laser reflects light instead of making physical contact), but hasn't changed much today (only more density and better lasers).

Still don't understand how an LD player recognizes an LD. If I put a CD-rom in one, would it really just start reading it and send the waveform to all the carriers? Would be useful for reverse engineering Playstation game copy protection, and maybe others.

If you research FM modulation then you'll understand how the pits and lands work for the original LD format. All the digital stuff was incorporated into LD 20 plus years later. Original LD players do not recognize CD or digital LD tracks. LD originally did not have digital tracks. New players incorporated new and old technology so you can play both. Stop thinking LD was developed in the digital age.

Yup, the core LD format, at least for CAV encoding, was pretty much locked down in late 1976 - blam1 has a playable set of prototype disks from early 1977. It just happened that CD audio 'fit' into the format with a little massaging later on.

Perhaps in an alternate universe there are analog video Blu-Rays, but even with their anti-scratch coating they'd probably still need to be in caddies, and there would be wild variations in quality. LD was a tough beast to wrangle/produce compared to DVD and Blu-Ray, it was just the best thing around for home video for almost 20 years

But in this universe, digital processing of 1080P is very easy - the Roku 2 XD/XS and Raspberry Pi both use the same outdated cell phone processor and it can even encode 1080P video off a camera.

The pits and lands on LD are variable, so they do not produce a square wave. Its an FM signal. FM is not digital.



The opposite would be true. Converting everything to a binary system with effective digital compression is way way more space efficient.



SACDs, like most optical disc formats, does owe something to LD since it was the first commercial format anything like it. Other than that, the same similarity to CD, MD, PSP, DVD, Bluray, etc, I can't think of any similarities.



Off the top of my head, I can't think of any. I suppose Laserfilm is sorta similar (in that a laser produces an FM signal from varying pits and lands) but also way different (its made of chemical process film, not stamped into a disc, also the laser shines straight through Laserfilm).



There are multiple ways. On a more modern player (one that plays CDs) it first determines the size of the disc by setting it on the spindle. There are photosensors or plastic tabs that let the player know what size the disc is. Then, once its spinning, there is a TOC that identifies disc type.




Not any more useful than any other disc transport. You're either going to get nothing (if the player is modern enough to play CDROMs), a combination of nothing with audio tracks (if the game has redbook audio) or a whole bunch of really loud noise (older players) that isn't really useful for data analysis. A physical hack would be needed, in which case you might as well use anything. Regardless, I think Playstation encryption was completely hacked 15 years ago.

Disclord's stated that Laserfilm is the same encoding, and could be played on a gas tube player with a special reflective disk. I guess someone could actually make a 'new' Laserdisc this way, but it would be terribly impractical. It'd be easier overall to create a digital-sourced composite video player using USB or SD card media, since later LD players digitize the video signal anyway.

I can't think of anything else that went into production that used analog encoding with an optical pickup. I suspect an analog compact disc would have been feasible especially with CX, but digital technology was already advanced enough to handle audio in the early 80's.

disclord @ Capricorn One (1978) [PSE96-076]

Apologies for resurrecting an ancient thread, but...

It would seem to me that the duration of the pits/lands of a laserdisc could be digitally captured as a stream of duration values. This stream could then be processed fully in the digital domain to extract highly precise video frame data. The pit/land duration sampling rate could be high enough to assure precision in excess of that required to extract the data via FFT and other applicable algorithms, mathematically, resulting in a "perfect" DIGITAL extraction. Perfect is in quotes, because one still needs to deal with the whole sub-sampled chroma and interleaved video issues of a composite signal...

The laserdisc processing in a laserdisc player (like the CLD-97) is analog in the front end (laser pick-up) and then conversion to digital at 8 bit resolution (crap?), for timebase correction, pausing, etc, then conversion back to analog composite for output. That means that tolerance of components and design of the analog paths, and 8 bit digitization, influence the quality of playback...

But if the capture was a tap off of the laser pick-up amplifier followed by direct conversion of pit durations... there would be NO impact to quality from the player video path, and one COULD put out a precision digital video stream, post processed as desired fully in the digital domain. This assumes one sampled at a high enough sample rate to capture the "infinitely variable pits/lands" durations.

Bottom line, at the format level, a laserdisc is basically digital... pit on, pit off, with a duration that can be represented with an appropriately high sampling rate. And, it CAN be ripped, and processed in the digital domain...

I wonder if the crosstalk issues could actually be processed out using this method as well by sampling the stream with more than just a discrete on/off, but with actual voltage sampling of the laser pick-up output, then one could identify the 'minor' contributions of crosstalk and back them out prior to sampling the primary pit durations... Maybe one could restore poorly mastered discs this way... without resorting to image scanning the disc... just with a normal player.

We have the processing power these days...

Anyone "analog" enough to look at the CLD-97 laser pick-up circuit and find a point to tap off a buffered full frequency signal that can be digitized, and design the buffer that could be "loaded" with an appropriate high speed 8 -12 bit ADC? To be honest, one probably wouldn't need 8 bit ADC resolution, only enough to discern the crosstalk variation, since we're just looking for pit/land length values... High speed ADCs are an everyday thing now, as are ghz op-amps, and MPSoC FPGA's to post process the sampled stream...

Bottom line... you could basically digitally process the whole disc via a normal LD player, and put it out on an HDMI port, including the AC3, DTS and 16 bit digital AND digitized analog streams. And at this point in technology, you could probably put the whole thing right in the player itself and add an HDMI port. AND do it all real-time..

- Melifluonze

The above is mostly covered already by the Domesday Duplicator and ld-decode projects. It just isn't realtime.

Perfect! I'll go search it out! I didn't come across it in my initial searches.

Thanks so much!

Actually, Domesday is similar, but different. Right, "ld decode" is not real-time, and I'm talking about modding a player to "scan" the disc (play it normally) and skip the aging video electronics of the player. In other words, turn it into a digital transport for every day use...

As a mattet of fact, the crappiest player would probably provide a video stream as good as the best player...

I'm going to start investigating... seems like all you'd want in the player itself is the pick-off circuitry and the initial raw data stream, output over a standard interface like USB (version dependent on data rate needed), and an external decoder/ processor.

If I get anywhere, I'll start a thread...

Found LD Decode thread... from Happycube. Way cool! He captured the RF output with a video capture card.

Yes, and if the player is actually spinning a disc that’s probably the most logical way to do it.

Your idea of recording the lengths of the pits and lands...I’m pretty sure it’s a dead end. The player doesn’t see pits and lands. It has no idea how long they are. The total package of the disc and the laser and all of the support components are needed to generate the EFM signal. It just shines a light at a wobbly mirror, and knows not how the mirror came to wobble. It would take a lot more work to measure the microscopic nature of the disc AND to model the analog circuit that normally makes something useful out of it.

HOWEVER, I am optimistic that someday we will be able to simply photograph/scan the entire side of the disc at once and use software to not only do what you describe but also “play” the spiral back from the single super high res picture. In that scenario what you’re talking about would have to be part of the chain.

Yeah. The red laser units might have an advantage over the infrared ones though.

I guess it would depends on how good the post processing is. Noise is noise and crappy floppy late model decks make lots of noise that will be as prominent in the raw EFM as it is the the composite video we see coming out it. To put it another way, you can put a $1000 phono amp on a Crosley and it’s still going to sound like it has a plastic tone arm.

Good example.