How is data stored on a Laserdisc? (1 Viewer)

[Matt Stone]

This isn't a really important question, but my friend and I were talking about it the other day. Is the video an MPEG2 stream...or what, and is the audio stored similarly to the audio on DVDs?

Thanks for the info.

 

[Marc Rochkind]

It's not MPEG-2. For all the gory details, see Laserdisc FAQ: http://www.cs.tut.fi/~leopold/Ld/FAQ/

 

[JohnnyG]

That's certainly a nice FAQ, but I couldn't find a section that actually explained how the technology works. Perhaps I just didn't look hard enough?

I know that Laserdisc is an analog medium, but that's about it.

 

[Matt Stone]

I couldn't find it either.

 

[RAF]

The video on a Laserdisc is analog and is stored in composite form. That's why you don't necessarily get a better picture by using the S-Video video output on the player. It all depends where the better comb filter (the device that separates the composite video for viewing on your monitor) is located.
If the best comb filter is in your LD player then use S-Video out from it. If the best comb filter is in your monitor, then use the composite output from the player to the monitor. There's an easy way to check all this out. Try it both ways and see what looks better to you. One rule of thumb is that the newer piece of equipment probably has the better quality comb filter, but this is not a hard-fast rule. In my case the 3D Comb Filter in my Sony VW10HT is one of the finest comb filters ever used in a consumer product so I actually feed composite into my projector for the best LD images.
In other words, unlike sources that store the video in separated (Chroma & Luminance) form, like VCRs and camcorders, there is not always a benefit from using an S-Video connection. In fact it might produce a poorer picture for the reasons stated above.
This might be more than you wanted to know, but since it's all related I figured that I'd throw it out there for general information.
Hope this helps.

 

[Allan Jayne]

I am not sure how it is modulated on subcarriers but the video on laserdisk is not compressed, it has all 525 lines per pair of even-odd 480i video fields (for NTSC) recorded as composite video on a continuous spiral of data working from the inside of the disk to the outer edge. There are two analog and I think 2 digital audio channels included also, suitably modulated on subcarriers. I am not sure how the analog video is represented as pits on the aluminized layer inside the LD which are comparable to the pits on the similar layer of a CD or DVD.
The video and audio normally comes off the disk and goes to the player outputs in real time, that is, the video is not processed and is supposed to be a correct composite video signal, timed correctly to match the scanning of the electron beam in the TV it is going to. The upscale players do some refining of the video, for example time base correction, to be sure all the scan lines start precisely at the correct time despite minute wow or flutter in the disk rotation.
Video hints:
http://members.aol.com/ajaynejr/video.htm

 

[Rachael B]

All LD players have Time Base Correctors, some better than others.

 

[Don Munsil]

For what it's worth, the analog video and audio on a laserdisc is encoded with pulse width modulation (PWM). The video & aduio is sampled, but not digitally. The length of the pit is controlled by the sample amplitude. Long pit=high amplitude. Short pit=low amplitude. LDs predate PCM and CDs, but not sampling theory.

The digital audio tracks on an LD are essentially equivalent to the digital audio tracks on a CD, and use pulse code modulation. The pits indirectly represent 0s and 1s that combine into a 16-bit number, representing the sample amplitude.

Don

 

[Matt Stone]

Okay...so video uses PWM. That speaks to my knowlege as a computer nerd. I get it now. Thx.