Laserdisc questions (alt history)

[roxics]

I’m fascinated by alt history ideas related to technology. Like what if this technology had developed instead of this. But I’m terrible with the math.
For example, the Laserdisc came out in 1978, the CD in 1982. The former was analog and the latter digital. Close enough in time to be the same era. So what if the laserdisc had been the size of a CD. How small would the laser need to be to fit that analog video and audio onto a 120mm CD sized disc versus the typical 300mm sized laserdisc? Would a blu-ray laser be small enough? Is it even possible?

Both the Analog laserdisc and the digital CD use a 780nm laser according to what I’ve read. That could be wrong, but same era, so I believe it. Blu-ray is 405nm.

If it is possible, let me further complicate the question with two more add-ons:
1. What if you put both sides of the laserdisc on one side of the CD sized disc? How much smaller would the laser be then?
2. What if it were high definition like the MUSE HD laserdiscs. Would that even be possible?

I’m just fascinated but the idea of analog video on a disc, especially something the size of a CD/DVD/Blu-Ray.

My last question is more realistic.
Is there any downside to analog video read by a laser in regards to long term storage. As in, outside of disc rot, does the video degrade in any way. In other words, is there any benefit to digital in this way or drawback to the video being analog?

[roxics]

Yeah I figured these would be a bit outside the scope of what might be asked here. Just finding people who know what laserdisc is anymore, let alone asking some very technical and hypothetical questions related to it.

Oh well. If someone ever does find this and have an answer, you're awesome!

[bigass]

With analog, when you lose part of the signal, the signal gets worse. You could reorient your TV antenna to get a better signal, but your TV would still cope with a crappy one and display it the best it could. Videotape running through a machine with gears and belts and spinning heads might vary in timing a little here and there, and your TV would be happy enough with it because it was analog, and analog is always dealing with things like noise, flutter, and things not being quite on-spec.

With digital, the signal can sometimes degrade a little more before things get too dire. After all, the material is digital. Something and not-something. Ones and zeros. Pits and lands. One volt or no volts. Even if that one volt is a little less than one volt, it's pretty easy to tell whether it's an ON or OFF, vs. analog where everything is on a continuum between absence of signal and full signal. Like, you can see a stoplight better in the fog than a billboard. The light is on or off but the billboard is a whole image that's being obscured by the fog.... ok, my metaphors are getting weak.

Moreover, there's no video on that digital disc. There's just digital data. That data could be anything, but we've decided that we're going to use this form factor and data standard to hold video and use it for that. Remember that the DVD was actually Digital Versatile Disc-Video, and the CD was Compact Disc-Digital Audio. They're just data storage with an agreed-upon use.

Videodisc actually put the video on the disc. Not compressed files that turn into pictures when uncompressed -- there's an analog video signal encoded right onto the big rainbow platter! Holy crap! Nifty stuff.

[roxics]

I mean no offense, but I know all of that, I'm curious what your point is?

What I want to know is if we can fit 30-120+ minutes of analog video (SD and possibly HD) and stereo analog audio on a CD sized disc and if so what size laser do we need?

I'm looking for the technical specifications or even just to know it's possible or not.

[bigass]

Ok.

No, you can't.

Cheers.

[roxics]

I don't think there is any technical reason why we shouldn't be able to, we would just need a small enough laser. I'm just not sure how small. Then again maybe there is something I'm missing and it's not possible for some reason. In which case I would like to know what that reason is.