Thursday, April 5, 2012

How much data ( converted to Digital ) was stored on a Laserdisc?

Here is a question just asked recently over on a Facebook Fan Page. I've seen this question  ( or subject matter)  several dozen times before though out the years, and have often wondered the same thing myself.  
Truth be told -
 I've attempted several times before to answer this question in a dozen or so different comments, but I was afraid my responses would just get buried (and it did ) and therefore no one would ever read it.  Discovering the answer to the question  required tons of research, because the answer wasn't so clean cut.  While I don't claim to be an expert on the subject, what follows is THE BEST possible answer I've been able to piece together from many different sources.
 I've  added my personal two cents at the end of this read.   For all those fans over on Laserdisc Forever, LD Vault, and LDDB, this one is for you then. 
T2: LaserDisc, DVD & Blu-ray

From the top, we know:
The picture signal that the Laservision disc (LVD), or Laserdisc (LD) carries is actually analog in format. that's right - ANALOG. Just like vhs. More really- more like S-VHS. ( Right now- some Hi8 or Beta lover is screaming! )  Therefore, it's really can't be measured in MB's or GB's, because those are really only Digital storage measurements, but we will get to that shortly. 
Only the LPCM audio tracks are digital, and those can be/ and are measured in MB's, at the Redbook standard at 1411kbps. Later, DTS disc were encoded at 1440kbps for all 5.1Tracks.

Now- standard pre recorded CD's are  74mins long ( yes- most CD-R disc can now store up to 80mins of music in this format- but many player's have issues w/ burnt data at the extremities edge of the disc ) and hold 700MB, then that’s just a bit ( pun intended )  shy of 1MB per min, so rounding up, a CLV disc could hold an hour of LPCM sound per side, so that could be said to =  just shy of 600MB's per side for sound. Yes? OK? 

OK. Now we will deal with the analog encoded video portion of the disc. How do we compare a system that stored the analog video on a surface covered with oval pits (CLV had 30 Billion pits, the spiral from the center out is get this - 24 miles long ! & the laser reads this information at something like 424 inches per sec) in order to reproduce the stored video picture with that of a digital storage medium? Well that's the real trick.

LVD, or LD and DVD (Stamped) are vastly different.
 LD pit size is 1.6um and the gap space between them ( the pits) was huge, something like 1.3um's. DVD, on the other hand, uses a 650 nm wavelength laser diode light as opposed to a 780 nm for LD. This permits a smaller pit to be etched on the media surface compared to CDs (0.74 µm), allowing in part for DVD's increased storage capacity. The gap spacing is also less.

In comparison, Blu-ray Disc, uses a wavelength of 405 nm, and one dual-layer disc has a 50 GB storage capacity. As far as the gap is concerned,  look at like an older 50in 720 Plasma display TV, ( or- - if you happen to still have one of those micro LCD / DLP 720p projection sets)  and compare it side by side to a 1080p newer 4K UHD set.  In the same amount space, the 1080p set has Twice the amount of pixels than that of the 720p, (1920 X 1080, compared to 1280 X 760.  Or, in other words, 2.2 megapixels, verse a megapixel) all because of gap spacing. You will see that the gaps between the pixels on the 720 display are far larger than the 1080. So,  what this means is that a  "pixel" can be different sizes, depending on the size and resolution of your TV screen - or the throw from your LCD/DLP front projector to the wall - which will effect the size of both the picture and pixel you see projected.
  The new Ipad  now has 3 times the amount of pixels in it screen than a 1080p HDTv! So, I guess what I'm trying to say is - that a pit, is not always "a pit" because the sizes and gaps in the pits of the different storage formats are different. Get it ?...........................

Anyways, that is why Laserdisc are so large !
 Now, If they were to go back and use the same size disc with a 405nm laser that’s used for Blu-ray, and modern day encoding systems, then everything simply becomes a simple matter of surface area. Of course, the Blu-ray disc has the double layer capability that LD never had, and the pits are ever so much smaller, and the gap spacing is almost non-existent by comparison.
But since the LD is 2.5 larger than a Blu-ray disc, IF they were to STAMP an HD LVD today, I'd say she could store about 130GB a side or 260GB total- but that’s just my best guess, of course. 

MOVING ON -
This was copied and pasted  from an AVS form written by "DOS Guy” years ago, dealing w/ the subject of comparing  LD's storage VS a compact-disc- in which he stated: 
"So, if the information encoded onto a laserdisc represented digital data (0s and 1s), how much data would it hold?  A LD is 30 cm, so roughly 10.6 cm is the central hub. Let's also assume that the outermost 2 mm aren't recorded on.  The radius of a LD becomes 14.8 cm, so Pi x 14.8^2 = 688.13 cm2, minus the central hub radius of 5.3 cm, Pi x 5.3^2 = 88.25 cm2, for a total recordable surface area of about 599.89 cm2. If we assume that the LD used the same laser (as a CD) to read tracks of the same width, then the LD also has an areal density of 7.298 MB/cm2, giving a laserdisc about 4.276 GB a side, or 8.551 GB total, back and front."

 "Although you can't compare analog and digital, 
the result is nevertheless interesting. A laserdisc requires the equivalent of 4.3 GB of digital data to encode 60 minutes of information, whereas a DVD encodes 120 minutes of video in 4.7 GB, and that video yields a higher resolution (720x480 for DVD, vs. 560x480 for LVD) thanks to a finer laser and MPEG-2 compression, which is made possible by “digital data” instead of analog data." 

So the storage cap is about the same, the video just takes up that much more room. So, if we subtract the 576MB for digital audio tracks, we are left with 3.7 GB’s. How much of that space is used for the 2 analog sound channels? Well, we know that a Dolby AC-3 5.1 384kbps track will fit into one, so multiply that by 2, and that’s 768kbps (like adding the equivalent of a standard DVD DTS Track) or, just a little less than half of the LPCM tracks, at 276MB. So 3.7 GB -.276GB for CX analog tracks and we are left with: 
3.4 GB for an hour of Video!

That same 411 can easily fit into a much smaller space today. (2.2GB for Video) Take that same information (560x480) w/ 420 scan lines, and convert it to DVD, like, for instance, the very latest Re-release ( not the original )  6 -disc Box Set of Season One of the X-files, which I STRONGLY believe to be nothing more than a Laserdisc Dub! 

 I have the Pilot episode on LD, and A/B ing the two   ( I plugged my LD-V8000 Laserdisc player into the Tosh DVD recorder's input, and did nothing more that switch from the pre-recorded store bought DVD ( which was playing in the recorder) to "Input One" source on the Tosh, so we were not viewing a Laserdisc transfer, but the Laserdisc itself through the recorder- which has built in HDMI output to my Panasonic 26in 720p HD LCD.)  I could see no difference between them at all, in terms of resolution -much like most of original 1st release of Star Trek: The Next Generation on DVD. ( Which I also believe to be sourced from the Laserdisc release)  Even though both these series were shot on Kodak 35mm film, those elements were transferred to D-1 /2 Digital video tape    ( for both editing, cost, and special effects reasons @ the time) and those limitation show on these releases. 

The only way I knew I was watching the DVD version & NOT the LD source was that the Laserdisc ( by nature of the format) are brighter than their DVD counterparts, and the Black level on the Laser was nowhere near as dark as the DVD.  Thanks to finer laser, smaller pits, less gap, MPEG 2 COMPRESION, & the Dual Layer format (w/ 9.4GB’s of storage), "they " managed to transfer four - 50 minute long episodes of The X-files , or 2 full Laserdiscs - both sides (on LVD, each 50 min episode resides on one single side of a disc) onto one Single DVD. Keep in mind, that in order to do this, the LPCM audio track is converted and reduced to a mere Mp3 quality 2.0 Dolby Digital Stereo track. Still, there you have it. 

Original X-file LaserVideoDisc Back-cover.


Oh, one last thought.
 Know who you can thank for "Digital Copy", the "feature that's not a feature?" Steve Jobs? Nope. Sony. Yep, good old Sony. See "they" developed this compression format known as H.264MPEG4, the very one used for, yep, you guessed it - Blu-ray. However, back in the day (2004) before a High Cap disc came along, "they" wanted to make movies "portable", and presto , the UMD , the little mini Digital Media Disc, based upon the MD, was created, for the PSP, with a storage space of 1.8 GB, and ATRAAC3 plus encoded (bad, very bad) 128kps 2 ch sound. Sound familiar? Sound a little like the same spec sheet as your Digital Copy?
 That's because, for the most part, it is:


 The format almost took off, but Sony limited it's playback capabilities to the PSP, and I guess people really don't want to own disc that small. Maybe the kids lose them? I don't know? Like Laserdisc, production of the UMD has come to an end. Unlike Laserdisc, people don't seem to be collecting these things. Heck, the newer PSP's stream video over WI-FI at the same data rate.

 Although "Digital Copy" (1.6 GB's MAX of video data)(that's right, a memory card or USB stick holds way more today) benefits from being "transferred and mastered from" an Hi Def source",
 which (besides being viewed on a smaller screen then our big screen TV's) is why the picture holds up.          
The 32GB version of This Class10 SD card: $10bucks.
This one stores more data than One Standard BRD,
or- nearly 14 DVD's. OH-it' data tranfer rate is also faster.
It's could hold 40 of your "Digital Copy" movies.
   

 Of course-
 "Digital Copy" is really just another way for the studio's to "attempt to"
 control their product.
Only StarTrek TNG film not on LD

Which is another story, altogether.
             END
For more info on Digital copy: 
read this:  http://www.sonypictures.com/residentevil/bonuscopy/faq.html