Glenn's Junk Chest

An assortment of Glenn's writings, photography, gaming resources, flash movies, and other creative output.

Friday, January 07, 2005

Copyright: Audio from DVDs

I know nothing about such things but plan to be learning soon. Is there a way to pull a music/audio track off a DVD and burn to a CD? (We will soon have both a DVD and CD burner)
Short answer: yes.

Medium answer: Yes, if it's a commercial DVD, you'll need a utility called a DVD ripper that allows you to pull the audio track of the DVD, and then another utility to convert the audio into something you can burn easily to a CD.

Long answer: Yes, but it may be illegal to do so, even if you own the DVD and your use of the music/audio would otherwise be considered fair use under copyright law. There are two possible reasons for this, neither of which has been adequately challenged legally.

The first reason is that the studio does not consider you to "own" the DVD in question at all, they consider you to be using it under "license". As a result, they have attempted to prohibit certain actions that you would normally be able to perform under the law. Since you have never agreed to the terms of this license, probably even implicitly, this is mostly deceitful bullshit, but I'm not a lawyer, so you do this at your own risk. Unfortunately, it doesn't seem to be against the law for them to falsely claim that you're not allowed to do certain things with what you bought, even if those things are perfectly legal, such as making a backup copy.

The second reason is more complex. When the DVD format was released, the studios were hesitant to embrace the format for fear of perfect digital copies expanding the already significant role that piracy, especially in Asia, plays in that industry. Since nothing can be done about the Asian problem, or large-scale psuedo-commercial piracy ventures, the studios insanely decided to attack the much lesser problem of "casual" piracy. Since people that pirate videos routinely are hardly even slowed by their measures, the effort, like most copy-protection, damages law-abiding customers the most.

Their approach to this was two-pronged. The first part is that every DVD player manufactured is supposed to be part of the DVD consortium, and the manufacturer pays a one million dollar fee to the consortium to get encryption codes to read the content off of commercial DVDs. Only software with the code can read the DVD, thus, computers wouldn't be able to easily copy the data in a useful form. This had the side-effect of almost completely stopping any "small" video operations which couldn't pony up the fee, such as a free open-source DVD player for linux. This scheme is called the Content Scrambling System (or CSS).

The second part of the approach was legislative. Using the various lawmakers that Hollywood and the music industry have in their pocket, an inane piece of legislation generally referred to as the Digital Millenium Copyright Act (DMCA) was passed. While the bad (or at least corporate-serving) provisions of this law are too numerous to account here, one of them is highly relevant. Under this law, it is illegal to "traffic" in devices or software intended to circumvent copy protection. In other words, even if your use of the data from the DVD would be otherwise clearly and indisputedly legal, such as making a CD to listen to in your car, the acquistion and distribution of the software or hardware necessary to perform the act is a crime.

Now, there are those of us in the tech community (most of us, probably) that don't think it's OK to backhandedly take away our fair use rights by making it illegal to acquire the tools needed to exercise those rights. This is like assuring us that it's still legal to travel freely, while making it illegal to buy and sell cars. As a result, a _lot_ of work has gone into circumventing the copy protection on DVDs. Because the people designing or implementing the system were relatively inept, and in part because the US export regime at the time prevented the use of any truly strong encryption, the encryption has been cracked, and the keys and software necessary to decode a DVD are now generally available. A number of programs for both the Mac and PC will take a DVD and extract the tracks from it. If you're on a Macintosh, I recommend going to Version Tracker, and typing "DVD" into the search box. I've heard good things about MacTheRipper, however, though I'm unsure of its suitability to audio-only extraction.

OK, once you've "ripped" the DVD, you'll have a bunch of files to deal with. Here's a guide to the types of files you may see.

.VOB - this is a dvd-format video and audio file. If you've got this, you'll need another tool to extract the audio/video tracks from it if you want to work with them seperately. A .VOB file may be all you need if you're making another DVD, however.

.PCM - this is an unencoded audio file. It's similiar to a CD audio file, but I believe it's at 48Mhz instead of 44.1Mhz. You won't see this very often, because such files use too much space on disk when multiple audio tracks are desired. If you do see one, it's probably a good place to start, because it's encoding is relatively simple. Many audio programs can probably convert this into something CD burnable quickly and easily.

.AC3 - this is a dolby digital encoded audio file. The encoding is fairly complex, and it can include anywhere between 1 and 8 tracks of audio. The most commonly found will be 2 (left and right) or 5+1 (left, right, center, back-left, back-right, + low frequency effects). This format is proprietary, but many tools out there can be used to convert it into a stereo file that can be burned to a CD. Try and find a good tool, as simply taking the left and right channels out of a 5.1 mix is going to result in dialogue that's too quiet, you'll need to mix in some of the center channel to both left and right. Good software should handle this automatically. There may be multiple audio tracks, so be careful to get the one that's in English.

.DTS - this is a Digital Theatre Sound Encoded file. They're less common, and should always be accompanied by an .AC3 as well. Unless you know something I don't, stick with the AC3.

.m2v - this is MPEG2 video with no audio.

.m2a - this is a MPEG2 audio file. DVDs for the US market aren't supposed to have these, but DVDs sold in Europe might. There was some liscensing or patent problem that caused this, but I don't remember the details.

One final note: the DVD consortium requires that all DVD players support an analogue copy-protection scheme on the outputs called Macrovision. Any commercial DVD producer that wants to pay a small fee can turn it on with a single bit on any disc. This is pretty meaningless if you're going to "rip" the DVD as above, but is a real problem if you want to, say, copy a DVD onto a video tape. That said, I don't believe that macrovision has any effect whatsoever on the audio outputs of the DVD player. So, if all the above is proving too much, you really ought to be able to hook up the DVDs audio outputs to the audio inputs of your computer, and simply record the whole thing in a CD-friendly format and burn it. There will be more quality loss, but probably not a lot, and may be easier than any of the above for certain purposes, especially if this is a one-time deal.


At 2:21 PM, Blogger Jon said...

How do you hold all of this information in your head and where do you get it?

At 12:20 PM, Blogger Victoria JK Dunn said...

I was really only looking for the short answer..........

At 10:52 AM, Anonymous Anonymous said...

Yeah, well, you managed to hit one of Glenn's core knowledge issues. Sometimes it's like pushing a button and all that info comes out.



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