User:Ryan Cooley/MPEG1: Difference between revisions
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MPEG-1 articles (MPEG-1, MP1, MP2, MP3) on wikipedia are complete crap. Disorganized, slanted, incomplete, misconstrued, etc. | MPEG-1 articles (MPEG-1, MP1, MP2, MP3) on wikipedia are complete crap. Disorganized, slanted, incomplete, misconstrued, etc. | ||
It's far easier to start from scratch than try to fix all the individual existing ones, and will give far better end results; I will | It's far easier to start from scratch than try to fix all the individual existing ones, and will give far better end results; I will use ''some'' small bits of content from the existing articles. | ||
'''Do not make any changes to this page''' for now. | '''Do not make any changes to this page''' for now. | ||
This is my mind-dump and accommodating others before I'm done will just make much, much more work for me. Put any suggestions on the Talk page, and I will eventually address them. | This is my mind-dump and accommodating others before I'm done will just make much, much more work for me. Put any suggestions on the Talk page, and I will eventually address them. -RC | ||
-RC | |||
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Perhaps the most well-known part of the MPEG-1 standard today is the MP3 audio format it introduced. | Perhaps the most well-known part of the MPEG-1 standard today is the MP3 audio format it introduced. | ||
The MPEG-1 standard is published as [[ISO/ | The MPEG-1 standard is published as [[ISO/IEC 11172]]. | ||
== History == | == History == | ||
Modeled on the successful collaborative approach and technologies developed by the [[Joint Photographics Expert Group]] | Modeled on the successful collaborative approach and the compression technologies developed by the [[Joint Photographics Expert Group]] and [[CCITT]]'s [[Experts Group on Telephony]] (creators of the [[JPEG]] image compression standard and the [[H.261]] standard for [[video conferencing]] over [[ISDN]] lines respectively) the [[MPEG]] working group was established in January 1988. MPEG was formed to address the need for [[standard]] video and audio encoding formats, and build on H.261 to get better quality through the use of more complex (non-[[realtime]]) encoding methods. <ref>http://www.cis.temple.edu/~vasilis/Courses/CIS750/Papers/mpeg_6.pdf pp.2</ref> | ||
Development of the MPEG-1 standard began in [[May 1988]]. 14 video and 14 audio codec proposals were submitted by individual companies and institutions for evaluation. The codecs were extensively tested for computational complexity and subjective (human perceived) quality, at (combined video+audio) data rates of 1.5Mbps. The codecs that excelled in this testing were utilized as the basis for the standard and refined further, with additional features and other improvements being incorporated. <ref>http://www.chiariglione.org/mpeg/meetings/santa_clara90/santa_clara_press.htm</ref> | Development of the MPEG-1 standard began in [[May 1988]]. 14 video and 14 audio codec proposals were submitted by individual companies and institutions for evaluation. The codecs were extensively tested for computational complexity and subjective (human perceived) quality, at (combined video+audio) data rates of 1.5Mbps. The codecs that excelled in this testing were utilized as the basis for the standard and refined further, with additional features and other improvements being incorporated. <ref>http://www.chiariglione.org/mpeg/meetings/santa_clara90/santa_clara_press.htm</ref> | ||
After 20 meetings of the full group in various cities around the world, and 4 <sup>1</sup>/<sub>2</sub> years of development and testing, (a draft standard was produced September 1990, and only minor changes were introduced) the final standard was approved in early [[November 1992]]. <ref>http://www.chiariglione.org/mpeg/meetings.htm</ref> Before the MPEG-1 standard had even been finalized | After 20 meetings of the full group in various cities around the world, and 4 <sup>1</sup>/<sub>2</sub> years of development and testing, (a draft standard was produced September 1990, and only minor changes were introduced) the final standard was approved in early [[November 1992]]. <ref>http://www.chiariglione.org/mpeg/meetings.htm</ref> Before the MPEG-1 standard had even been finalized, work began on a second standard, [[MPEG-2]], intended to extend MPEG-1 technology to provide full broadcast-quality at high bitrates (3 - 15 [[Mbps]]), and support for [[interlaced]] video. <ref>http://www.chiariglione.org/mpeg/meetings/london/london_press.htm</ref> Due in part to the similarity between the two codecs, the MPEG-2 standard included full backwards compatibility with MPEG-1 video. | ||
Today, MPEG-1 is by far the most widely compatible lossy audio/video format in the world. Due to its age, most patents on MPEG-1 Video and Layer II audio technology have expired (MP3 being a notable exception), and can be implemented without payment of license fees in almost all countries. Most computer software for video playback includes MPEG-1 decoding, in addition to any other supported formats. The immense popularity of MP3 audio has established a massive [[installed base]] of hardware that can playback all 3 layers of MPEG-1 audio. The widespread popularity of MPEG-2 (mostly with broadcasters) means MPEG-1 is playable by most digital cable/satellite set-top-boxes, and digital disc and tape players. | Today, MPEG-1 is by far the most widely compatible lossy audio/video format in the world. Due to its age, most patents on MPEG-1 Video and Layer II audio technology have expired (MP3 being a notable exception), and can be implemented without payment of license fees in almost all countries. Most computer software for video playback includes MPEG-1 decoding, in addition to any other supported formats. The immense popularity of MP3 audio has established a massive [[installed base]] of hardware that can playback all 3 layers of MPEG-1 audio. The widespread popularity of MPEG-2 (mostly with broadcasters) means MPEG-1 is playable by most digital cable/satellite set-top-boxes, and digital disc and tape players. | ||
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Notably, the MPEG-1 standard very strictly defines the [[bitstream]], and decoder function, but does not define how MPEG-1 encoding is to be performed (although they did provide a reference implementation). This means that MPEG-1 coding efficiency can drastically vary depending on the encoder used, and generally means that newer encoders perform significantly better than their predecessors. | Notably, the MPEG-1 standard very strictly defines the [[bitstream]], and decoder function, but does not define how MPEG-1 encoding is to be performed (although they did provide a reference implementation). This means that MPEG-1 coding efficiency can drastically vary depending on the encoder used, and generally means that newer encoders perform significantly better than their predecessors. | ||
== Application == | == Application == | ||
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== Video == | == Video == | ||
Part 2 of the MPEG-1 standard covers video and is defined in [[ISO/ | Part 2 of the MPEG-1 standard covers video and is defined in [[ISO/IEC 11172-2]] | ||
== D-frames == | |||
MPEG-1 has a unique frame type not found in later video standards. D-frames or DC-pictures are independent images (intra-frames) that have been encoded DC-only (AC coefficients are removed) and hence are very low quality. D-frames are never used/referenced by I, P or B frames. D-frames are only useful for fast previews of video, for instance when seeking through a video at high speed. | |||
Given moderately higher performance decoding equipment, this feature can be approximated by processing I-frames, and discarding the AC coefficients before display. | |||
=== DCT === | === DCT === | ||
Each 8x8 macroblock is encoded using the ''Forward'' | Each 8x8 macroblock is encoded using the ''Forward'' Discrete Cosign Transform ([[FDCT]]). This process by itself is lossless, and is reversed by the ''Inverse'' DCT ([[IDCT]]) upon playback to produce the original values. | ||
The FDCT process converts the 64 uncompressed pixel values (brightness) into 64 different ''frequency'' values. One large value that is average of the entire 8x8 block (the '''DC coefficient''') and 63 smaller, positive or negative values (the '''AC coefficients'''), that are relative to the value of the DC coefficient. | The FDCT process converts the 64 uncompressed pixel values (brightness) into 64 different ''frequency'' values. One large value that is average of the entire 8x8 block (the '''DC coefficient''') and 63 smaller, positive or negative values (the '''AC coefficients'''), that are relative to the value of the DC coefficient. | ||
The (large) DC coefficient remains mostly consistent from one block to the next, and can so can be compressed quite effectively. A significant number of the AC coefficients will be 0, which can then be | The (large) DC coefficient remains mostly consistent from one block to the next, and can so can be compressed quite effectively. A significant number of the AC coefficients will be near 0, which can then be more efficiently compressed in a later step. Additionally, the frequency conversion is necessary for the quantization step. | ||
=== Quantization === | === Quantization === | ||
A quantization table is a string of 64-numbers (0-255) that tells the encoder what visual information is important, and which is not. Each number corresponds to a certain frequency component of the video image. | A '''quantization table''' is a string of 64-numbers (0-255) that tells the encoder what visual information is most important, and which is not. Each number corresponds to a certain frequency component of the video image. | ||
Each | Each of the 64 ''frequency'' values of the DCT block are divided by their corresponding value in the quantization table. This reduces the information in some frequencies, deemed less visually important, while other frequency components may be eliminated completely. This quantization process usually reduces a significant number of the ''AC coefficients'' to zero. | ||
This quantization process eliminates a large amount of data, and is the main lossy processing step in MPEG-1 video encoding. This is also the source of most MPEG-1 video artifacts, like [[blockiness]], [[color banding]], noise, [[ringing]], discoloration, et al. when video is encoded with an insufficient bitrate. | This quantization process eliminates a large amount of data, and is the main lossy processing step in MPEG-1 video encoding. This is also the source of most MPEG-1 video artifacts, like [[blockiness]], [[color banding]], noise, [[ringing]], discoloration, et al. when video is encoded with an insufficient bitrate. | ||
=== Lossless Data Compression === | |||
Several steps in the encoding of MPEG-1 video are lossless, meaning they will be reversed on decoding to produce exactly the same values. Since these lossless data compression steps don't add noise into or otherwise change the video (unlike quantization), it is often called [[noiseless coding]]. | |||
=== RLE === | |||
[[Run-length encoding]] (RLE) is a very simple method of compressing repetition. Given a string of "333333333" RLE would replace it with the values "3,9" simply telling the decoder to replace it with "333333333". RLE is very effective after quantization, as a significant number of the AC coefficients are zero, and can be represented in the file with just a couple bytes. | |||
=== Huffman coding === | |||
The data is then analyzed to look for strings that repeat often. Those strings are then put into a table. Wherever those strings are found in the data, they are replaced by a (much smaller) reference to the location in the table. | |||
Dimentions 4094x4094 | Dimentions 4094x4094 | ||
Datarate | Datarate | ||
| Line 80: | Line 86: | ||
Complexity (memory) | Complexity (memory) | ||
Delay | Delay | ||
GOP | GOP | ||
Keyframe placement | Keyframe placement | ||
Quantization* | Quantization* | ||
Ringing (large coefficients in high frequency sub-bands) | Ringing (large coefficients in high frequency sub-bands) | ||
zigzag | zigzag | ||
Macroblocks | Macroblocks | ||
16 dimentions | 16 dimentions | ||
Motion Vectors/Estimation | Motion Vectors/Estimation | ||
Black borders/Noise | Black borders/Noise | ||
| Line 105: | Line 100: | ||
Two MV per macroblock (forward/backward pred) | Two MV per macroblock (forward/backward pred) | ||
Prediction error | Prediction error | ||
Blockiness | |||
CBR/VBR | CBR/VBR | ||
Spacial Complexity | Spacial Complexity | ||
Temporal Complexity | Temporal Complexity | ||
| Line 124: | Line 115: | ||
*[[Bitrate]]s: 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320 and 384 kbit/s | *[[Bitrate]]s: 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320 and 384 kbit/s | ||
"digital frames of 1152 sampling intervals" | |||
mono, stereo, joint stereo (impulse, m/s), dual. | mono, stereo, joint stereo (impulse, m/s), dual. | ||
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It saw limited adoption in it's time, and most notably was used on the defunct [[Digital Compact Cassette]]. Layer I audio files will most often use the extension '''.mp1''' | It saw limited adoption in it's time, and most notably was used on the defunct [[Digital Compact Cassette]]. Layer I audio files will most often use the extension '''.mp1''' | ||
=== Layer II === | === Layer II === | ||
| Line 160: | Line 140: | ||
32 sub-bands | 32 sub-bands | ||
Exceeds MP3 somewhere between 192-256 kbps | Exceeds MP3 somewhere between 192-256 kbps | ||
Revision as of 09:20, 19 March 2008
MPEG-1 articles (MPEG-1, MP1, MP2, MP3) on wikipedia are complete crap. Disorganized, slanted, incomplete, misconstrued, etc. It's far easier to start from scratch than try to fix all the individual existing ones, and will give far better end results; I will use some small bits of content from the existing articles.
Do not make any changes to this page for now. This is my mind-dump and accommodating others before I'm done will just make much, much more work for me. Put any suggestions on the Talk page, and I will eventually address them. -RC
MPEG-1 was an early standard for lossy compression of video and audio. It was designed to compress raw video and CD audio to 1.5Mb/s without discernible quality loss, making Video CDs and Digital Video Broadcasting possible.
Perhaps the most well-known part of the MPEG-1 standard today is the MP3 audio format it introduced.
The MPEG-1 standard is published as ISO/IEC 11172.
History
Modeled on the successful collaborative approach and the compression technologies developed by the Joint Photographics Expert Group and CCITT's Experts Group on Telephony (creators of the JPEG image compression standard and the H.261 standard for video conferencing over ISDN lines respectively) the MPEG working group was established in January 1988. MPEG was formed to address the need for standard video and audio encoding formats, and build on H.261 to get better quality through the use of more complex (non-realtime) encoding methods. [1]
Development of the MPEG-1 standard began in May 1988. 14 video and 14 audio codec proposals were submitted by individual companies and institutions for evaluation. The codecs were extensively tested for computational complexity and subjective (human perceived) quality, at (combined video+audio) data rates of 1.5Mbps. The codecs that excelled in this testing were utilized as the basis for the standard and refined further, with additional features and other improvements being incorporated. [2]
After 20 meetings of the full group in various cities around the world, and 4 1/2 years of development and testing, (a draft standard was produced September 1990, and only minor changes were introduced) the final standard was approved in early November 1992. [3] Before the MPEG-1 standard had even been finalized, work began on a second standard, MPEG-2, intended to extend MPEG-1 technology to provide full broadcast-quality at high bitrates (3 - 15 Mbps), and support for interlaced video. [4] Due in part to the similarity between the two codecs, the MPEG-2 standard included full backwards compatibility with MPEG-1 video.
Today, MPEG-1 is by far the most widely compatible lossy audio/video format in the world. Due to its age, most patents on MPEG-1 Video and Layer II audio technology have expired (MP3 being a notable exception), and can be implemented without payment of license fees in almost all countries. Most computer software for video playback includes MPEG-1 decoding, in addition to any other supported formats. The immense popularity of MP3 audio has established a massive installed base of hardware that can playback all 3 layers of MPEG-1 audio. The widespread popularity of MPEG-2 (mostly with broadcasters) means MPEG-1 is playable by most digital cable/satellite set-top-boxes, and digital disc and tape players.
Notably, the MPEG-1 standard very strictly defines the bitstream, and decoder function, but does not define how MPEG-1 encoding is to be performed (although they did provide a reference implementation). This means that MPEG-1 coding efficiency can drastically vary depending on the encoder used, and generally means that newer encoders perform significantly better than their predecessors.
Application
VCD players DVB DAB MP3 MPEG-2? audio: SVCD DVD players (not surround) ATSC/HDTV (failed)
Video
Part 2 of the MPEG-1 standard covers video and is defined in ISO/IEC 11172-2
D-frames
MPEG-1 has a unique frame type not found in later video standards. D-frames or DC-pictures are independent images (intra-frames) that have been encoded DC-only (AC coefficients are removed) and hence are very low quality. D-frames are never used/referenced by I, P or B frames. D-frames are only useful for fast previews of video, for instance when seeking through a video at high speed.
Given moderately higher performance decoding equipment, this feature can be approximated by processing I-frames, and discarding the AC coefficients before display.
DCT
Each 8x8 macroblock is encoded using the Forward Discrete Cosign Transform (FDCT). This process by itself is lossless, and is reversed by the Inverse DCT (IDCT) upon playback to produce the original values.
The FDCT process converts the 64 uncompressed pixel values (brightness) into 64 different frequency values. One large value that is average of the entire 8x8 block (the DC coefficient) and 63 smaller, positive or negative values (the AC coefficients), that are relative to the value of the DC coefficient.
The (large) DC coefficient remains mostly consistent from one block to the next, and can so can be compressed quite effectively. A significant number of the AC coefficients will be near 0, which can then be more efficiently compressed in a later step. Additionally, the frequency conversion is necessary for the quantization step.
Quantization
A quantization table is a string of 64-numbers (0-255) that tells the encoder what visual information is most important, and which is not. Each number corresponds to a certain frequency component of the video image.
Each of the 64 frequency values of the DCT block are divided by their corresponding value in the quantization table. This reduces the information in some frequencies, deemed less visually important, while other frequency components may be eliminated completely. This quantization process usually reduces a significant number of the AC coefficients to zero.
This quantization process eliminates a large amount of data, and is the main lossy processing step in MPEG-1 video encoding. This is also the source of most MPEG-1 video artifacts, like blockiness, color banding, noise, ringing, discoloration, et al. when video is encoded with an insufficient bitrate.
Lossless Data Compression
Several steps in the encoding of MPEG-1 video are lossless, meaning they will be reversed on decoding to produce exactly the same values. Since these lossless data compression steps don't add noise into or otherwise change the video (unlike quantization), it is often called noiseless coding.
RLE
Run-length encoding (RLE) is a very simple method of compressing repetition. Given a string of "333333333" RLE would replace it with the values "3,9" simply telling the decoder to replace it with "333333333". RLE is very effective after quantization, as a significant number of the AC coefficients are zero, and can be represented in the file with just a couple bytes.
Huffman coding
The data is then analyzed to look for strings that repeat often. Those strings are then put into a table. Wherever those strings are found in the data, they are replaced by a (much smaller) reference to the location in the table.
Dimentions 4094x4094 Datarate Constrained Parameters Bitstream
Luma Chroma
I-frames (Intraframe) Seeking P-frames (Predicted) B-frames (Bidirectional) Complexity (memory) Delay
GOP Keyframe placement
Quantization* Ringing (large coefficients in high frequency sub-bands) zigzag Macroblocks 16 dimentions Motion Vectors/Estimation Black borders/Noise pel precision (half pixel IIRC) Two MV per macroblock (forward/backward pred) Prediction error Blockiness CBR/VBR Spacial Complexity Temporal Complexity
Audio
Part 3 of the MPEG-1 standard covers audio and is defined in ISO/IEC_11172-3
MPEG-1 audio utilizes perceptual masking with sub-band coding with a polyphased filter bank to reduce the bitrate of the audio stream. It has been shown to be particularly efficient on high quality percussive sounds (impulses) thanks to the very effective time-domain concealment characteristics of its 32 sub-band polyphased filter bank.
- Sampling rates: 32, 44.1 and 48 kHz
- Bitrates: 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320 and 384 kbit/s
"digital frames of 1152 sampling intervals"
mono, stereo, joint stereo (impulse, m/s), dual. efficient time-domain concealment characteristics
Layer I
MPEG-1 Layer I is nothing more than a simplified version of Layer II, designed for low-delay and low complexity to facilitate real-time encoding on the hardware available in 1990 for applications like teleconferencing and studio editing. With the substantial performance improvements in digital processing since, it has now been long obsolete.
It saw limited adoption in it's time, and most notably was used on the defunct Digital Compact Cassette. Layer I audio files will most often use the extension .mp1
Layer II
Despite some 20 years of progress in the field of digital audio coding, MP2 remains the preeminent lossy audio coding standard due to its especially high audio coding performances on highly critical audio material such as castanet, symphonic orchestra, male and female voices and particularly high quality percussive sounds (impulses) like triangle and glockenspiel. Testing has shown MP2 to be equivalent or superior to than much more recent audio codecs, such as Dolby Digital AC-3. [5]
Subjective audio testing by experts, in the most critical conditions ever implemented, have shown MP2 to offer transparent audio compression at 256kbps for 16-bit 44.1khz CD audio. [6] That (approx) 1:6 compression ratio for CD audio is particularly impressive since it's quite close to upper theoretical limit of Perceptual Entropy, at just over 1:8. [7] [8] Achieving much higher compression is simply not possible without discarding some perceptible information.
audio broadcasting error resilient Musicam 32 sub-bands Exceeds MP3 somewhere between 192-256 kbps
Layer III/MP3
9 months? ASPEC (Fraunhoffer) freq transform encoder entropy coding Hybrid MDCT pre-echo worse aliasing issues "aliasing compensation" mid/side (or impulse) joint stereo 576 frequency components selectivity "If there is a transient, 192 samples are taken instead of 576 to limit the temporal spread of quantization noise"? psychoacoustic model and frame format from MP1/2 ringing CBR/VBR Frames are not independent
Systems
Part 1 of the MPEG-1 standard covers systems which is the logical layout of the encoded audio, video, and other bitstream data.
"The MPEG-1 Systems design is essentially identical to the MPEG-2 Program Stream structure." [9]
Program Stream Interleaving PES Wrap-around DTS Timebase correction Pixel/Display Aspect Ratio
See Also
References
- ↑ http://www.cis.temple.edu/~vasilis/Courses/CIS750/Papers/mpeg_6.pdf pp.2
- ↑ http://www.chiariglione.org/mpeg/meetings/santa_clara90/santa_clara_press.htm
- ↑ http://www.chiariglione.org/mpeg/meetings.htm
- ↑ http://www.chiariglione.org/mpeg/meetings/london/london_press.htm
- ↑ Wustenhagen et al, Subjective Listening Test of Multi-channel Audio Codecs, AES 105th Convention Paper 4813, San Francisco 1998
- ↑ http://www.faqs.org/faqs/mpeg-faq/part1/ "You can compress the same stereo program down to 256 Kbits/s with no loss in discernable quality." (the original papers would be much, much better refs, but I can't seem to find them! This just proves they exist!)
- ↑ J. Johnston, Estimation of Perceptual Entropy Using Noise Masking Criteria, in Proc. ICASSP-88, pp. 2524-2527, May 1988.
- ↑ 6. J. Johnston, Transform Coding of Audio Signals Using Perceptual Noise Criteria, IEEE J. Sel. Areas in Comm., pp. 314-323, Feb. 1988.
- ↑ http://www.chiariglione.org/mpeg/faq/mp1-sys/mp1-sys.htm
External Links
- http://www.chiariglione.org/mpeg/ Official Home Page of the Moving Picture Experts Group (MPEG) a working group of ISO/IEC