[lelpep]

Forgive me if this seems a silly question but,

if a standard blank DVD has a 2 hour maximum capacity in standard play mode, how come some movie DVD,s have much more than 2 hour running times on the one DVD?
Are they compressed to extended play or more?

[spiney2]

Usually, they're double layer dvds.

Otherwise, there's no "maximum" playing length! However, if you increase playing time, you decrease picture quality.

[grahamlthompson]

As Spiney2 says they use dual layer, you can however use dual layer blanks in up to date burners anyway. Very usefull for burning around 40 mins of HD in AVCHD to

[captainkremmen]

Commercial DVDs are normally dual layer. The top layer is slightly see through, your DVD player's laser focuses on the top layer, plays it through, then when it reaches the end the laser is refocused to see through the top layer on to the bottom layer. This is why most DVD players have a slight pause during a movie as the laser is refocused.

[gemma-the-husky]

it isnt that they have a rigid 2hour limit anyway (unlike a CD which does have a time limit, irrespective of compression level)

single layer, a DVD has a capacity of 4.7Gb

at normal play compression (I think they call it SP - Standard play) this works out at a about 2hrs 8mins or so.

by changing the compression you can get more or less time - so most DVD recorders offer a LP mode, which gives about 4hrs, at sort of VHS quality, or a XP mode, which only gives an hour - although generally its hard to discern much difference between the SP and XP modes.

Sony eg, have about 12 standard modes, offering levels of compression varying between these.

[David (2)]

pre-recorded dvd has a capacity of 4.25Gb for a single sided, single layer disc, or 8.5Gb for a single sided, dual-layer disc.

Blank dvds that your record on at home are inferior to this offering only 1Hr per single sided, single layer disc in BEST (XP) recording mode. You have to rely on compression confusingly refered to as SP/LP/EP (taken from the tape era) to up this to 2, 4, and 6hrs. On tape, using LP mode would double the time on a tape (3-6hr, or 4-8hr depending on tape length) simply by runnning the tape at half speed. The effect was to simply make the image softer. Compression on blank dvd introduces the lego or blocky effect where the quality is cut out the recording. These effects are much more visible to the human eye than a slightly softer image that tape offered.

[figrin_dan]

Those mentioning 2 hours are, I believe, referring to a dvd recording on a dvd recorder type set top box. This records at quite a high bitrate as it is encoding to MPEG live (via analogue).

Pre recorded dvds are encoded over a longer time and so can be better quality at lower bitrates.

It's also possible to record the MPEG stream directly onto a dvd (with additional headers etc), to play on a dvd player. This transport stream has a fairly low bitrate - due to broadcasting constraints - so you can get a fair amount on one dvd. I'm not sure if any standalone dvd recorders work this way, but you can do this with a Toppy and PC.

[iknowitall1]

Quote:

Originally Posted by David (2)

pre-recorded dvd has a capacity of 4.25Gb for a single sided, single layer disc, or 8.5Gb for a single sided, dual-layer disc.

Blank dvds that your record on at home are inferior to this .

Not quit true as recordable dual layer blanks also have 8.5Gb of capacity.

Pioneer recorders have 10 fixed levels offering up to 10 hours on a disc but I've not tried it as the quality would be appalling.
They also have a flexible recording mode that lets you record for any length of time in between the hours to maximise quality.

All my single layer discs are labelled as 4.7Gb.
My laptop and Pioneer recorder read as 4.4Gb for a single layer.

[lelpep]

Thanks for all the useful information, seems to cover most things..

[scottie55]

Quote:

Originally Posted by gemma-the-husky

it isnt that they have a rigid 2hour limit anyway (unlike a CD which does have a time limit, irrespective of compression level).

That's very misleading. It's only true if you adopt the "Red Book" standards. Adopt other standards and the time limit increases just as it does for DVDs.

Quote:

Originally Posted by gemma-the-husky

although generally its hard to discern much difference between the SP and XP modes.

Not on my kit - it's like chalk and cheese.

[iknowitall1]

Quote:

Originally Posted by scottie55

That's very misleading. It's only true if you adopt the "Red Book" standards. Adopt other standards and the time limit increases just as it does for DVDs.



Not on my kit - it's like chalk and cheese.

Depends on what you are recording.
Regular digital tv looks almost the same in XP as it does in SP not least of all because the bitrates they use are low to start with.

Having said that , the 70's Top of the Pops I recorded in XP from German digital tv really look better , but German tv always looks better than ours right back to the days of analogue satellite

[gemma-the-husky]

scottie

a music CD is time limited, isnt it - I dont mean a CD of data or MP3's. I mean a normal music CD that will play on any normal; CD player.

i didnt think a DVD was limited in the same way. Just that the recorded bit-rate affected the size of the file, and therefore affects the total recording time that can be accomodated on a DVD. And I cannot discern much difference between a SP recording and a XP recording.

[scottie55]

Yes, that's true but, as I understand it, that's because what you mean by a "normal music cd" is a "red book stereo audio cd".

What you stated is misleading because it confuses the phyisical CD media with it's logical content.

[pocatello]

Commercial dvds are encoded with vbr. They also have the luxury of time to potentially do things like 2 pass encoding to squeeze quality into less space. You cannot do that well on the fly with dvd recorders off tv without a harddrive. So home deck type dvd recorders can be recording at a higher constant bitrate because of the real time nature and cheap processors they have to deal with at that price point.

[grahamlthompson]

Quote:

Originally Posted by pocatello

Commercial dvds are encoded with vbr. They also have the luxury of time to potentially do things like 2 pass encoding to squeeze quality into less space. You cannot do that well on the fly with dvd recorders off tv without a harddrive. So home deck type dvd recorders can be recording at a higher constant bitrate because of the real time nature and cheap processors they have to deal with at that price point.

No problem with vbr if you use a pc, it just takes a lot longer to create because of the two pass analysis of the content required.

[captainkremmen]

Quote:

Originally Posted by gemma-the-husky

scottie

a music CD is time limited, isnt it - I dont mean a CD of data or MP3's. I mean a normal music CD that will play on any normal; CD player.

i didnt think a DVD was limited in the same way. Just that the recorded bit-rate affected the size of the file, and therefore affects the total recording time that can be accomodated on a DVD. And I cannot discern much difference between a SP recording and a XP recording.

In essence you are right. Philips (who developed CD in partnership with Sony) now control the rights to the CD standard and logos. A CD has to conform to the Red Book standard which ensures compatibility with all CD players. A modern CD that fully conforms will still play on a 1985 CD player for example. The standard was tight and allowed no real deviation to ensure this compatibility. You might notice that some modern CDs do not carry the "Compact Disc-Digital Audio" logo because they deviate from the standard (usually because of added copy protection or extra features). Philips will not allow the logo to be used on discs that do not fully conform to the Red Book standard, although the standard was updated at the end of the 90s to allow for such things as CD-Text.

DVD is different, it is a set of standards that allows quite a bit of variation. Variation in video resolution and bitrate as well as supporting the original MPEG-1 video standard along with the newer MPEG-2, variation in audio bitrates as well as allowing three audio standards (AC3, Mpeg Audio and PCM) are all within specifications. It can get quite confusing . Incidentaly the original DVD specifications did not allow for DTS Audio, so DVDs that carried DTS audio weren't standard. All DVD players can handle PCM, AC3 and Mpeg Layer II audio but many older players cannot handle the DTS bitstream because it isn't part of the standard, and it isn't necessary for manufacturers to include it. Most do these days, in fact I don't think I know of any company that doesn't allow a DTS bitstream to be output.

Slight correction: Mpeg Audio was to be the standard in Europe with AC3 in the US. However European DVD players could pretty much all handle AC3 as well as Mpeg Audio so AC3 quickly became the standard. Some very early DVD players could only handle either Mpeg or AC3 audio but all DVD players since can handle both.

[spiney2]

yeah!

With cds, the technology then avialable didn't allow audio compression - with varying fidelity - so, the time was set by the sampling process ....... which gave a limited number of fixed lengths!

[gemma-the-husky]

the point i was trying to make was that DVD's are not limited to 2 hrs recording, as the OP thought - and in fact SD recording generally manages slightly more than 2hrs, which can be handy.

[spiney2]

DVDs have a finite capacity, but you vary the compression .......

[iknowitall1]

Quote:

Originally Posted by captainkremmen

Some very early DVD players could only handle either Mpeg or AC3 audio but all DVD players since can handle both.

While there were some discs that had only MPEG sound and no DD I don't know of any players that didn't come with DD.

The Panasonic A100 was the first player in the UK and that had DD sound .

I think that the DD/MPEG issue had been resolved before players became generally available and players before that played it safe.

I still have a disc or two with MPEG sound

[Kodaz]

Quote:

Originally Posted by gemma-the-husky

unlike a CD which does have a time limit, irrespective of compression level

"Ordinary" CDs (i.e. ordinary Audio CDs that work on a standard CD audio player) don't use compression (*) as such, they store uncompressed PCM, 16-bit 44.1 kHz sampled data (i.e. fixed resolution, fixed sample rate). That's why they have a fixed capacity.

80 minutes is the most you can reliably store on an audio CD in this way.

Quote:

Originally Posted by scottie55

That's very misleading. It's only true if you adopt the "Red Book" standards. Adopt other standards and the time limit increases just as it does for DVDs.

(Translation for non-geeks; "red book" was the standard that defined the original audio CD format we know and love.)

Well... you know what he meant. Sure, you can store music in MP3 format and the like on a recordable CD-R (or read it from a CD-ROM), but most people would take the OP's comment to refer to standard audio CDs, which MP3-compressed audio (or anything else) on a CD-ROM isn't.

(*) Where compression here means "squeezing more into a given space" and not dynamic range compression, which is something totally different.

[captainkremmen]

Quote:

Originally Posted by iknowitall1

While there were some discs that had only MPEG sound and no DD I don't know of any players that didn't come with DD.

The Panasonic A100 was the first player in the UK and that had DD sound .

I think that the DD/MPEG issue had been resolved before players became generally available and players before that played it safe.

I still have a disc or two with MPEG sound

I'm sure I remember one of the home cinema magazines reviewing one very early DVD player that only had mpeg sound, but I am almost positive it recommended not buying though as an agreement had been reached to allow AC3 sound on European players by then. It may just have been a prototype or import though.