dragoman
24th March 2002, 10:32
Hi,
I begin this topic kind of open-ended. I was thinking about DVD, which uses MPEG-2 compression, and the fact that most people use it as the de-facto ideal in video quality. (Notice I said most people, to those who bristle at any mention of an all-inclusive idea)
Anyway, since I was drunk at the time, I'm kind of surprised I remembered it. But I did, and here is what I have found out:
DVD (Digital Versatile Disc, or Digital Video Disc as most people call it....officially it doesn't stand for anything :) ) uses MPEG-2 video compression, as most of you know.
First, some background on DVD:
Physcial specifications of a DVD (http://www.mpeg.org/MPEG/DVD/Book_A/Specs.html)
Very technical explanation of MPEG-2 workings (http://mpeg.telecomitalialab.com/standards/mpeg-2/mpeg-2.htm)
The question I am ultimately trying to answer is "Why is MPEG-2 regarded as the standard for video" and also "Is there anything better?"
Question 1: Why is MPEG-2 the standard?
From my research into the matter, MPEG-2 is a lossy compression method (like all MPEG formats) that uses a bitrate between 3.5 and 5 MB/sec. The DVD FAQ (http://www.thedigitalbits.com/officialfaq.html#1.3) states that better quality is achieved over 6 MB/sec (makes sense, it is a lossy format).
It seems to me that the reason that DVD has become the standard is a combination of three things: 1) MPEG-2 is the best way to compress the master video into a easily watchable format, 2) DVD provides a way to pack massive amounts of information (ie high bitrate video) into a package that is easily mass-produced, and 3) DVD offered a way to easily copy-protect the content, preventing (or at least reducing) movie piracy.
As it says on the DVD faq, video quality (especially video compressed using a lossy format such as MPEG) is subjective....one person's idea of good quality may not be another's. I base my assumption then that the decision to use the MPEG-2 format for DVD was based upon economic reasons rather than technical ones (this conclusion is also supported by the behavior of the MPAA in recent months).
One should also note that copy-protection was integrated into DVD from the start.
1) CSS (Content Scrambling System) prevents the data on the disc from being copied onto a computer's hard drive, unless the proper key was used to unlock the data. As we all know, this feature has been largely by-passed by now.
This feature was by-passed first by Linux users who wished to view DVD's on their computer system (something completely legal, btw) but were prevented by the fact that no software was yet-written to play DVD's on the Linux operating system. The Linux users by-passed the CSS encryption by developing De-CSS, which allowed them to copy the MPEG-2 files to their hard drives and thus watch movies. The resulting program, De-CSS was posted and distributed by 2600 Magazine, the mislabled (by the press) "hacker" website which has since stopped hosting the software (by federal decree). The MPAA has waged constant legal battles against anyone distributing this software on the internet (although we all know it's a moot point now).
Sidenote - How was CSS cracked?
The CSS system has a master list of 400 "keys" that are included on every CSS-encoded disc. The drive unit of a player is assigned it's own CSS decryption key, which must be licensed. This key is one of the 400 master keys, and is used to unlock the encryption on a disc which allows the player to decrypt and play the video. A "DVD-ripper" essentially does just that - it accesses the CSS keys on the disc and applies every one until the correct key is found, thus allowing the video to be copied onto the user's hard drive.
2) Another measure of copy protection was dubbed Macrovision. The correct term is APS, or "Analog Protection System", which is basically a circuit included in every DVD player ever sold. Macrovision adds a rapidly modulated colorburst signal ("Colorstripe") along with pulses in the vertical blanking signal ("AGC") to the composite video and s-video outputs (also component video). Macrovision may show up as stripes of color, distortion, rolling, black & white picture, and dark/light cycling. What this means is that it is virtually impossible to record a dvd onto a vhs tape without severe distortion occurring in the resulting video (using standard equipment).
The inclusion of this protection system was obviously intended to prevent the copying of dvd media onto vhs tapes (the so-called "Blockbuster pirates" - referring to those people who rent movies to tape them), and has been largely successful. Several computer programs have been developed to remove the copy protection from the digital video, and several standalone dvd players have appeared on the market with de-macrovision features (the most notable being the APEX 600A, which was later recalled by Apex Digital Inc. after protests from the MPAA were published). (Sidenote - the Apex 600A is no longer on the market, but future generations Apex players have the same function - my AD3210 has this feature to turn off the Macrovision).
3) Region codes. Region codes are not considered a form of copy protection by the MPAA, but the effects of this system cannot be considered anything else. One byte of data on a disc is given a certain value, one which corresponds to the values assigned DVD players sold in different regions around the world. The different region codes are as follows:
1: U.S., Canada, U.S. Territories
2: Japan, Europe, South Africa, and Middle East (including Egypt)
3: Southeast Asia and East Asia (including Hong Kong)
4: Australia, New Zealand, Pacific Islands, Central America, Mexico, South America, and the Caribbean
5: Eastern Europe (Former Soviet Union), Indian subcontinent, Africa, North Korea, and Mongolia
6: China
7: Reserved
8: Special international venues (airplanes, cruise ships, etc.)
A DVD player with a specific region code will play only DVD's with that region code. Software dvd players often offer the chance to change the region code up to a certain number of times, after which the last selected code becomes permanent. Hardware DVD players were region specific, until very recently. The aformentions Apex AD600A was a "multi-region" DVD player, which would play any region dvd (Sidenote - My Apex AD3210 plays all regions as well....to access this feature a hidden menu must be found).
The inclusion of the region code into the disc is entirely discretionary by the disc's maker, and is not required by law. However, most movie studios do so (after all, why not? They can charge higher prices in the US for Region 1 DVD's than they do in China for Region 6 dvd's, and vice versa...more money).
Content encoded without a region-code on the disc can be played on all players, regardless of region designation. However, these discs are hard to find and are normally made by independant film companies or are privately-generated.
*I know this seems to have become a dvd-piracy lecture, but bear with me....I prefer to be thorough)
One must understand that this point that the first four copy protection mechanisms explained here are not required by law to be used with DVD-discs.
Five copy-protection systems currently in development are mentioned below, but as they are not currently used they are not part of this discussion. Full explanation of them can be found at the DvD Faq (http://www.thedigitalbits.com/officialfaq.html#1.3).
These systems are:
Copy Generation Management System (CGMS)
Content Protection for Prerecorded Media (CPPM)
Content Protection for Recordable Media (CPRM)
Digital Copy Protection System (DCPS)
High-Bandwidth Digital Content Protection (HDCP)
This proves my third point above, that a reason for DVD to be used as a standard is the ability to copy-protect it's contents.
To move on to the second question, and the reason for this post:
"Is there anything better?"
Unfortunately, at the time a true lossless video compression technology does not exist in a consumer-applicable format (any developers reading this please correct me!).
Several formats that claim to have achieved lossless video compression include:
Autosophy compression (http://www.autosophy.com/videcomp.htm) - uses a "redefintion of information, based on object size and motion" - A few more technical details are on the site, but basically this is a stream-optimized video technology that only transmits information about things in a frame that have changed from one frame to the next. (Very similar to MPEG-4 video compression's use of keyframes). Promises to reduce bandwidth tremendously while preserving and even increasing quality of streaming video. Very interesting.
Matrox (http://www.matrox.com/videoweb/products/enduser/background/pdf/mathematically_lossless.pdf) has developed a "mathematically lossless compression" that delivers "better quality than uncompressed". Hard to believe, but the details are there. The term for the process is known as "entropy" encoding, which leaves the digital information unaffected, yet manages to compress the video at a rate of 1.6/1. (Note - requires Adobe acrobat reader)
There are many other "lossless" video compression formats out there (go to Google, you'll see for yourself), far too many to list or explain here.
But back to the original question. Is there something better than DVD?
Quality-wise, there must be. By defintion, MPEG-2 is a lossy format, which means that the video can be corrupted by the encoding process, and that data is lost. MPEG-2 can never (read, NEVER) be as good as the original master video.
A lossless compression system would have better results quality-wise than a DVD. However, such methods would probably result in a filesize greater than that of DVD, which requires more space to hold that information.
Advances in data storage are occurring at a rate that makes it conceivable that such massive amounts of data could be stored in a format easily marketed and used by the general public. That being said, it is conceivable that a lossless video format could replace DVD as the video "standard" for consumers in the future.
But I seriously doubt that this will happen in the near future. DVD is becoming entrenched in the consumer world, like CD did before it. After 22 years, CD-audio is still the standard audio format being sold today (although the Red-Book Audio Standard is far behind current audio formats in quality). DVD-Audio and Super Audio CD are two formats becoming more mainstream, but are not yet massively available.
DVD will be the same way, I predict. Certain video technologies will be created which are better in quality than DVD, but the DVD will remain the standard for years (and perhaps, decades) to come.
So the people out there who are constantly searching for better quality (I am one of them) will not be disappointed, but for the forseeable future we will continue to use DVD's as the source material for most of our encoding efforts, at least until the master source video for a movie is released to the public....
(wrapping up a very long post....whew!)
I invide comments, but please don't flame me....
dragoman
I begin this topic kind of open-ended. I was thinking about DVD, which uses MPEG-2 compression, and the fact that most people use it as the de-facto ideal in video quality. (Notice I said most people, to those who bristle at any mention of an all-inclusive idea)
Anyway, since I was drunk at the time, I'm kind of surprised I remembered it. But I did, and here is what I have found out:
DVD (Digital Versatile Disc, or Digital Video Disc as most people call it....officially it doesn't stand for anything :) ) uses MPEG-2 video compression, as most of you know.
First, some background on DVD:
Physcial specifications of a DVD (http://www.mpeg.org/MPEG/DVD/Book_A/Specs.html)
Very technical explanation of MPEG-2 workings (http://mpeg.telecomitalialab.com/standards/mpeg-2/mpeg-2.htm)
The question I am ultimately trying to answer is "Why is MPEG-2 regarded as the standard for video" and also "Is there anything better?"
Question 1: Why is MPEG-2 the standard?
From my research into the matter, MPEG-2 is a lossy compression method (like all MPEG formats) that uses a bitrate between 3.5 and 5 MB/sec. The DVD FAQ (http://www.thedigitalbits.com/officialfaq.html#1.3) states that better quality is achieved over 6 MB/sec (makes sense, it is a lossy format).
It seems to me that the reason that DVD has become the standard is a combination of three things: 1) MPEG-2 is the best way to compress the master video into a easily watchable format, 2) DVD provides a way to pack massive amounts of information (ie high bitrate video) into a package that is easily mass-produced, and 3) DVD offered a way to easily copy-protect the content, preventing (or at least reducing) movie piracy.
As it says on the DVD faq, video quality (especially video compressed using a lossy format such as MPEG) is subjective....one person's idea of good quality may not be another's. I base my assumption then that the decision to use the MPEG-2 format for DVD was based upon economic reasons rather than technical ones (this conclusion is also supported by the behavior of the MPAA in recent months).
One should also note that copy-protection was integrated into DVD from the start.
1) CSS (Content Scrambling System) prevents the data on the disc from being copied onto a computer's hard drive, unless the proper key was used to unlock the data. As we all know, this feature has been largely by-passed by now.
This feature was by-passed first by Linux users who wished to view DVD's on their computer system (something completely legal, btw) but were prevented by the fact that no software was yet-written to play DVD's on the Linux operating system. The Linux users by-passed the CSS encryption by developing De-CSS, which allowed them to copy the MPEG-2 files to their hard drives and thus watch movies. The resulting program, De-CSS was posted and distributed by 2600 Magazine, the mislabled (by the press) "hacker" website which has since stopped hosting the software (by federal decree). The MPAA has waged constant legal battles against anyone distributing this software on the internet (although we all know it's a moot point now).
Sidenote - How was CSS cracked?
The CSS system has a master list of 400 "keys" that are included on every CSS-encoded disc. The drive unit of a player is assigned it's own CSS decryption key, which must be licensed. This key is one of the 400 master keys, and is used to unlock the encryption on a disc which allows the player to decrypt and play the video. A "DVD-ripper" essentially does just that - it accesses the CSS keys on the disc and applies every one until the correct key is found, thus allowing the video to be copied onto the user's hard drive.
2) Another measure of copy protection was dubbed Macrovision. The correct term is APS, or "Analog Protection System", which is basically a circuit included in every DVD player ever sold. Macrovision adds a rapidly modulated colorburst signal ("Colorstripe") along with pulses in the vertical blanking signal ("AGC") to the composite video and s-video outputs (also component video). Macrovision may show up as stripes of color, distortion, rolling, black & white picture, and dark/light cycling. What this means is that it is virtually impossible to record a dvd onto a vhs tape without severe distortion occurring in the resulting video (using standard equipment).
The inclusion of this protection system was obviously intended to prevent the copying of dvd media onto vhs tapes (the so-called "Blockbuster pirates" - referring to those people who rent movies to tape them), and has been largely successful. Several computer programs have been developed to remove the copy protection from the digital video, and several standalone dvd players have appeared on the market with de-macrovision features (the most notable being the APEX 600A, which was later recalled by Apex Digital Inc. after protests from the MPAA were published). (Sidenote - the Apex 600A is no longer on the market, but future generations Apex players have the same function - my AD3210 has this feature to turn off the Macrovision).
3) Region codes. Region codes are not considered a form of copy protection by the MPAA, but the effects of this system cannot be considered anything else. One byte of data on a disc is given a certain value, one which corresponds to the values assigned DVD players sold in different regions around the world. The different region codes are as follows:
1: U.S., Canada, U.S. Territories
2: Japan, Europe, South Africa, and Middle East (including Egypt)
3: Southeast Asia and East Asia (including Hong Kong)
4: Australia, New Zealand, Pacific Islands, Central America, Mexico, South America, and the Caribbean
5: Eastern Europe (Former Soviet Union), Indian subcontinent, Africa, North Korea, and Mongolia
6: China
7: Reserved
8: Special international venues (airplanes, cruise ships, etc.)
A DVD player with a specific region code will play only DVD's with that region code. Software dvd players often offer the chance to change the region code up to a certain number of times, after which the last selected code becomes permanent. Hardware DVD players were region specific, until very recently. The aformentions Apex AD600A was a "multi-region" DVD player, which would play any region dvd (Sidenote - My Apex AD3210 plays all regions as well....to access this feature a hidden menu must be found).
The inclusion of the region code into the disc is entirely discretionary by the disc's maker, and is not required by law. However, most movie studios do so (after all, why not? They can charge higher prices in the US for Region 1 DVD's than they do in China for Region 6 dvd's, and vice versa...more money).
Content encoded without a region-code on the disc can be played on all players, regardless of region designation. However, these discs are hard to find and are normally made by independant film companies or are privately-generated.
*I know this seems to have become a dvd-piracy lecture, but bear with me....I prefer to be thorough)
One must understand that this point that the first four copy protection mechanisms explained here are not required by law to be used with DVD-discs.
Five copy-protection systems currently in development are mentioned below, but as they are not currently used they are not part of this discussion. Full explanation of them can be found at the DvD Faq (http://www.thedigitalbits.com/officialfaq.html#1.3).
These systems are:
Copy Generation Management System (CGMS)
Content Protection for Prerecorded Media (CPPM)
Content Protection for Recordable Media (CPRM)
Digital Copy Protection System (DCPS)
High-Bandwidth Digital Content Protection (HDCP)
This proves my third point above, that a reason for DVD to be used as a standard is the ability to copy-protect it's contents.
To move on to the second question, and the reason for this post:
"Is there anything better?"
Unfortunately, at the time a true lossless video compression technology does not exist in a consumer-applicable format (any developers reading this please correct me!).
Several formats that claim to have achieved lossless video compression include:
Autosophy compression (http://www.autosophy.com/videcomp.htm) - uses a "redefintion of information, based on object size and motion" - A few more technical details are on the site, but basically this is a stream-optimized video technology that only transmits information about things in a frame that have changed from one frame to the next. (Very similar to MPEG-4 video compression's use of keyframes). Promises to reduce bandwidth tremendously while preserving and even increasing quality of streaming video. Very interesting.
Matrox (http://www.matrox.com/videoweb/products/enduser/background/pdf/mathematically_lossless.pdf) has developed a "mathematically lossless compression" that delivers "better quality than uncompressed". Hard to believe, but the details are there. The term for the process is known as "entropy" encoding, which leaves the digital information unaffected, yet manages to compress the video at a rate of 1.6/1. (Note - requires Adobe acrobat reader)
There are many other "lossless" video compression formats out there (go to Google, you'll see for yourself), far too many to list or explain here.
But back to the original question. Is there something better than DVD?
Quality-wise, there must be. By defintion, MPEG-2 is a lossy format, which means that the video can be corrupted by the encoding process, and that data is lost. MPEG-2 can never (read, NEVER) be as good as the original master video.
A lossless compression system would have better results quality-wise than a DVD. However, such methods would probably result in a filesize greater than that of DVD, which requires more space to hold that information.
Advances in data storage are occurring at a rate that makes it conceivable that such massive amounts of data could be stored in a format easily marketed and used by the general public. That being said, it is conceivable that a lossless video format could replace DVD as the video "standard" for consumers in the future.
But I seriously doubt that this will happen in the near future. DVD is becoming entrenched in the consumer world, like CD did before it. After 22 years, CD-audio is still the standard audio format being sold today (although the Red-Book Audio Standard is far behind current audio formats in quality). DVD-Audio and Super Audio CD are two formats becoming more mainstream, but are not yet massively available.
DVD will be the same way, I predict. Certain video technologies will be created which are better in quality than DVD, but the DVD will remain the standard for years (and perhaps, decades) to come.
So the people out there who are constantly searching for better quality (I am one of them) will not be disappointed, but for the forseeable future we will continue to use DVD's as the source material for most of our encoding efforts, at least until the master source video for a movie is released to the public....
(wrapping up a very long post....whew!)
I invide comments, but please don't flame me....
dragoman