How can this fit on a single DVD?

mickbadal wrote on 6/18/2007, 4:39 PM

OK here's something I don't yet get with my limited knowledge of DVD formats, size and so forth, but I bet one of you wizards know the answer.

I have standard DVD-R 4.7GB discs. On the disc, they say "120 minutes". So according to the disc, a 4.7GB disc can hold 120 minutes (2 hours).

I made a backup of my Pixar "Incredibles" DVD to one of these DVD-R's (which I believe is close to 2 hours, not including special features and so forth). I used DVDShrink to decrypt & create the image on the HD, and then a program called "TMPGEnc DVD Author" to burn it to the disc (no additional compression applied, that I know of). Sure enough, it burns fine to my 4.7GB disc, and doesn't seem to suffer any data loss.

Yet when I create my own projects using VMS/DVDA, it can only fit about 1 hour of MPG2 on one of these DVD-R's (without using any "fit to disc" compression). Why can a single 4.7GB DVD-R fit a 2-hour movie, but only 1 hour of my own MPG2 files? What am I missing here?

I would love to be able to fit 2 hours of my own MPG2 video without using additional compression, as the professional movie seems to be able to do.

Thanks in advance for the lesson!

Comments

ScottW wrote on 6/18/2007, 5:07 PM

First off, the 120 minutes is just marketing. Ultimately, it's up to the bit rate that is used - something you don't have any control over with VMS except via the "fit to disk" option.

The lower the bitrate, the more info on the disk, but then also lower quality. How good things look at lower bitrates depends on the source material. Something like the Incredibles, which is extremely high quality source can probably handle lower bitrates without losing too much quality.

Also keep in mind that many commercially produced disks are almost always double layer.

--Scott

bStro wrote on 6/18/2007, 5:16 PM

What am I missing here?

Primarily, an understanding of "bitrates."

I find it annoying (or maybe disappointing, though not surprising) that DVDR manufacturers put copy on their product labels that state how much "time" the discs can hold while assuming that the buyer already understands the delicate relationship between "time" and "space." Or worse, intentionally wanting the buyer to think that there isn't one.

To wit: DVDs do not have a "time" limit (eg, 2 hours). They have a "space" limit (eg, 4.7GB). The way to fit more "time" into the amount of "space" you're given is to adjust the bitrate at which your video is encoded. Bitrate is the amount of data that the encoder (Vegas, DVD Architect, etc) will dedicate to each second of a video. The more data you let it dedicate per second, the better the quality of that video will be. (To a point. After a certain point, you've hit the quality peak and no increase in bitrate is going to make a difference.) At the same time, the more data you let the encoder dedicate per second (meaning, the higher a bitrate you use), the more disc space the file will take.

To get two hours on a 4.7GB disc, you'd want to use a bitrate of about 4800Mb/sec. Maybe less since DVDRs get kind of flakey near the edge, so it's best not to put any data there.

Sidenote: Don't strive to get as much video onto a disc as "the professional movies," and certainly don't hope to make it look as good. Those people start out with a super-high quality source and have super-expensive encoding systems. They can (and do) get the same quality at 3500Mb/sec that would take most of us 8000Mb/sec to achieve. Oh, and they all use dual layer DVDs, which hold 8.5GB, so they could go for the higher bitrate if they really felt like it.

Rob

Edit: Okay, so my "use a bitrate of 4800" advice isn't much help, as I neglected to notice that you're using VMS. And anyhow, Scott covered everything I did in a third the space. Or time.

Chienworks wrote on 6/18/2007, 7:00 PM

Or bits.

mickbadal wrote on 6/19/2007, 8:55 AM

Thanks everyone. I was already suspicious that it had something to do with bitrates. But I just couldn't understand how the professional movie folks could fit 2 hours onto a 4.7GB (single-sided) DVD and retain really good quality. So naturally I was wondering if I could somehow pull of the same thing - adjust my bitrate or something and get two hours on a 4.7GB, with good quality, like the pro movies.

But apparently the missing piece of the puzzle is the quality of the source of the pro's (allowing a lower bitrate), versus the quality of my source. So thanks for the clarification - I'll stick with 1hr per 4.7GB to retain my quality.

At least it seems I can burn a backup copy of (most?) of my 2-hour movies on a single sided DVD, so that's nice!

Terry Esslinger wrote on 6/22/2007, 6:40 PM

I just finished a DVD about emergency auto extrication that ran 1 hr 57min and placed it on a single DVD (4.7) by rducing the bitrate (in Vegas) to 4.9. The quality took a hit of course but it really was not that bad. Most of the people watching it did not notice the decreased quality. BTW the whole program went on for 3hr 45min. I tried using a DL DVD and placing it all on one DVD and while DVDA burned it and my computer would play it, I could not get a set top DVD player to play 'after the break'.

ScottW wrote on 6/22/2007, 10:11 PM

Layer breaks are a problem. I've had good luck with CopytoDVD setting the layer break correctly such that a player will play beyond the break.

Terry Esslinger wrote on 6/23/2007, 8:07 PM

Has anyone had good luck with DVDA setting layer breaks and what did you do?

KM wrote on 6/29/2007, 8:18 AM

I couldn't burn a DL disk until I updated my firmware. Once I updated, it burned perfectly. DVD-A gives the choice of which layer break to use and voila, it worked.

KM

Terry Esslinger wrote on 6/30/2007, 12:29 PM

KM,
Are you talking about the firmware for your burner?
I was actually able to 'successfully' (?) burn the DL disc, at least according to DVDA. But when I try to play it only plays the first layer and cannot play the second layer.
Terry