MPEG-2

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Not to be confused with MPEG-1 Audio Layer II (MP2).
MPEG-2 is used in Digital Video Broadcast and DVDs. The MPEG transport stream, TS, and MPEG program stream, PS, are container formats.

MPEG-2 (aka H.222/H.262 as defined by the ITU) is a standard for "the generic coding of moving pictures and associated audio information".[1] It describes a combination of lossy video compression and lossy audio data compression methods, which permit storage and transmission of movies using currently available storage media and transmission bandwidth. While MPEG-2 is not as efficient as newer standards such as H.264 and Opus, backwards compatibility with existing hardware and software means it is still widely used, for example in the DVD-Video standard.

Main characteristics[edit]

MPEG-2 is widely used as the format of digital television signals that are broadcast by terrestrial (over-the-air), cable, and direct broadcast satellite TV systems. It also specifies the format of movies and other programs that are distributed on DVD and similar discs. TV stations, TV receivers, DVD players, and other equipment are often designed to this standard. MPEG-2 was the second of several standards developed by the Moving Pictures Expert Group (MPEG) and is an international standard (ISO/IEC 13818). Parts 1 and 2 of MPEG-2 were developed in a collaboration with ITU-T, and they have a respective catalog number in the ITU-T Recommendation Series.

While MPEG-2 is the core of most digital television and DVD formats, it does not completely specify them. Regional institutions can adapt it to their needs by restricting and augmenting aspects of the standard. See Video profiles and levels.

Systems[edit]

MPEG-2 includes a Systems section, part 1, that defines two distinct, but related, container formats. One is the transport stream, a data packet format designed to transmit one data packet in four ATM data packets for streaming digital video and audio over fixed or mobile transmission mediums, where the beginning and the end of the stream may not be identified, such as radio frequency, cable and linear recording mediums, examples of which include ATSC/DVB/ISDB/SBTVD broadcasting, and HDV recording on tape. The other is the program stream, an extended version of the MPEG-1 container format without the extra overhead of previously mentioned transport stream designed for random access storage mediums such as hard disk drives, optical discs and flash memory.

Program stream exceptions are M2TS, which is used on Blu-ray discs, AVCHD on re-writable DVDs and HDV on compact flash cards all use the unnecessary overhead of a transport stream. While VOB on DVDs and Enhanced VOB on the short lived HD DVD do not waste storage space and just use the program stream. M2TS also adds an incompatible private extension of four network ordered bytes to the end of every transport stream packet, which is used as a random access timing reference for faster read times over using the Program Clock Reference contained in the adaption section of the primary stream.

MPEG-2 Systems is formally known as ISO/IEC 13818-1 and as ITU-T Rec. H.222.0.[2][3] ISO authorized the "SMPTE Registration Authority, LLC" as the registration authority for MPEG-2 format identifiers. The registration descriptor of MPEG-2 transport is provided by ISO/IEC 13818-1 in order to enable users of the standard to unambiguously carry data when its format is not necessarily a recognized international standard. This provision will permit the MPEG-2 transport standard to carry all types of data while providing for a method of unambiguous identification of the characteristics of the underlying private data.[4]

Video[edit]

Main article: H.262/MPEG-2 Part 2

The Video section, part 2 of MPEG-2, is similar to the previous MPEG-1 standard, but also provides support for interlaced video, the format used by analog broadcast TV systems. MPEG-2 video is not optimized for low bit-rates, especially less than 1 Mbit/s at standard definition resolutions. All standards-compliant MPEG-2 Video decoders are fully capable of playing back MPEG-1 Video streams conforming to the Constrained Parameters Bitstream syntax. MPEG-2/Video is formally known as ISO/IEC 13818-2 and as ITU-T Rec. H.262.[5]

With some enhancements, MPEG-2 Video and Systems are also used in some HDTV transmission systems.

Audio[edit]

MPEG-2 introduces new audio encoding methods compared to MPEG-1:[6]

MPEG-2 Part 3[edit]

Main article: MPEG-2 Part 3

The MPEG-2 Audio section, defined in Part 3 (ISO/IEC 13818-3) of the standard, enhances MPEG-1's audio by allowing the coding of audio programs with more than two channels, up to 5.1 multichannel. This method is backwards-compatible (also known as MPEG-2 BC[7][8][9][10]), allowing MPEG-1 audio decoders to decode the two main stereo components of the presentation.[11] MPEG-2 part 3 also defined additional bit rates and sample rates for MPEG-1 Audio Layer I, II and III.[12]

MPEG-2 BC (backward compatible with MPEG-1 audio formats)[7][8][11]

  • low bitrate encoding with halved sampling rate (MPEG-1 Layer 1/2/3 LSF - a.k.a. MPEG-2 LSF - "Low Sampling Frequencies")
  • multichannel encoding with up to 5.1 channels, a.k.a. MPEG Multichannel

MPEG-2 Part 7[edit]

Main article: Advanced Audio Coding

Part 7 (ISO/IEC 13818-7) of the MPEG-2 standard specifies a rather different, non-backwards-compatible audio format[9] (also known as MPEG-2 NBC[7][8][13]). Part 7 is referred to as MPEG-2 AAC. AAC is more efficient than the previous MPEG audio standards, and is in some ways less complicated than its predecessor, MPEG-1 Audio, Layer 3, in that it does not have the hybrid filter bank. It supports from 1 to 48 channels at sampling rates of 8 to 96 kHz, with multichannel, multilingual, and multiprogram capabilities.[6] Advanced Audio is also defined in Part 3 of the MPEG-4 standard.

MPEG-2 NBC (Non-Backward Compatible)[7][8]

  • MPEG-2 AAC
  • multichannel encoding with up to 48 channels

ISO/IEC 13818[edit]

MPEG-2 standards are published as parts of ISO/IEC 13818. Each part covers a certain aspect of the whole specification.

Part 1
Systems – describes synchronization and multiplexing of video and audio. (It is also known as ITU-T Rec. H.222.0.[2]) See MPEG transport stream and MPEG program stream.
Part 2
Video – compression codec for interlaced and non-interlaced video signals (Also known as ITU-T Rec. H.262).
Part 3
Audio – compression codec for perceptual coding of audio signals. A multichannel-enabled extension and extension of bit rates and sample rates for MPEG-1 Audio Layer I, II and III of MPEG-1 audio.
Part 4
Describes procedures for testing compliance.
Part 5
Describes systems for Software simulation.
Part 6
Describes extensions for DSM-CC (Digital Storage Media Command and Control).
Part 7
Advanced Audio Coding (AAC).
Part 8
10-bit video extension. Primary application was studio video. Part 8 has been withdrawn due to lack of interest by industry.
Part 9
Extension for real time interfaces.
Part 10
Conformance extensions for DSM-CC.
Part 11
Intellectual property management (IPMP)
MPEG-2 Parts[14][15]
Part Number First public release date (First edition) Latest public release date (edition) Latest amend- ment Identical ITU-T Rec. Title Description
Part 1 ISO/IEC 13818-1 1996 2013 2014[16] [17][18][19] H.222.0 Systems
Part 2 ISO/IEC 13818-2 1996 2013 H.262 Video
Part 3 ISO/IEC 13818-3 1995 1998 Audio MPEG-2 BC - backwards compatible with MPEG-1 Audio
Part 4 ISO/IEC 13818-4 1998 2004 2009[20] Conformance testing
Part 5 ISO/IEC TR 13818-5 1997 2005 Software simulation
Part 6 ISO/IEC 13818-6 1998 1998 2001[21] Extensions for DSM-CC extensions for Digital Storage Media Command and Control[22][23]
Part 7 ISO/IEC 13818-7 1997 2006 2007[24] Advanced Audio Coding (AAC) MPEG-2 NBC Audio - Non-Backwards Compatible with MPEG-1 Audio
Part 8 dropped 10-Bit Video The work was terminated because of low industry's interest.[25][26] It was started in recognition of the need to support studio-quality video signals quantized with 10 bits per component.
Part 9 ISO/IEC 13818-9 1996 1996 Extension for real time interface for systems decoders
Part 10 ISO/IEC 13818-10 1999 1999 Conformance extensions for Digital Storage Media Command and Control (DSM-CC)
Part 11 ISO/IEC 13818-11 2004 2004 IPMP on MPEG-2 systems Intellectual Property Management and Protection on the MPEG-2 system[27][28] (XML IPMP messages are also defined in ISO/IEC 23001-3[29])

History[edit]

MPEG-2 evolved out of the shortcomings of MPEG-1.

MPEG-1's known weaknesses:

  • An audio compression system limited to two channels (stereo).
  • No standardized support for interlaced video with poor compression when used for interlaced video
  • Only one standardized "profile" (Constrained Parameters Bitstream), which was unsuited for higher resolution video. MPEG-1 could support 4k video but there was no easy way to encode video for higher resolutions, and identify hardware capable of supporting it, as the limitations of such hardware were not defined.
  • Support for only one color space, 4:2:0.

Filename extensions[edit]

.mpg, .mpeg, .m2v, .mp2, mp3 are some of a number of filename extensions used for MPEG-1 or MPEG-2 audio and video file formats.

Applications[edit]

DVD-Video[edit]

Main article: DVD-Video

The DVD-Video standard uses MPEG-2 video, but imposes some restrictions:

  1. ^ 1.85:1 and 2.35:1, among others, are often listed as valid DVD aspect ratios, but are wider film aspects with letterbox style padding to create a 16:9 image
  • Allowed frame rates
    • 29.97 interlaced frame/s (NTSC)
    • 23.978 progressive frame/s (for NTSC 2:3 pull-down to 29.97[dvdrates 1])
    • 25 interlaced frame/s (PAL)
  1. ^ By using a pattern of REPEAT_FIRST_FIELD flags on the headers of encoded pictures, pictures can be displayed for either two or three fields and almost any picture display rate (minimum ⅔ of the frame rate) can be achieved. This is most often used to display 23.976 (approximately film rate) video on NTSC. See telecine for more information on how this works.
  • Audio + video bitrate
    • Video peak 9.8 Mbit/s
    • Total peak 10.08 Mbit/s
    • Minimum 300 kbit/s
  • YUV 4:2:0
  • Additional subtitles possible
  • Closed captioning (NTSC only)
  • Audio
    • Linear Pulse Code Modulation (LPCM): 48 kHz or 96 kHz; 16- or 24-bit; up to six channels (not all combinations possible due to bitrate constraints)
    • MPEG Layer 2 (MP2): 48 kHz, up to 5.1 channels (required in PAL players only)
    • Dolby Digital (DD, also known as AC-3): 48 kHz, 32–448 kbit/s, up to 5.1 channels
    • Digital Theater Systems (DTS): 754 kbit/s or 1510 kbit/s (not required for DVD player compliance)
    • NTSC DVDs must contain at least one LPCM or Dolby Digital audio track.
    • PAL DVDs must contain at least one MPEG Layer 2, LPCM, or Dolby Digital audio track.
    • Players are not required to play back audio with more than two channels, but must be able to downmix multichannel audio to two channels.
  • GOP structure (Group Of Pictures)
    • Sequence header must be present at the beginning of every GOP
    • Maximum frames per GOP: 18 (NTSC) / 15 (PAL), i.e. 0.6 seconds both
    • Closed GOP required for multi-angle DVDs

HDV[edit]

Main article: HDV

HDV is a format for recording and playback of high-definition MPEG-2 video on a DV cassette tape.

MOD and TOD[edit]

MOD and TOD are recording formats for use in consumer digital file-based camcorders.

XDCAM[edit]

Main article: XDCAM

XDCAM is a professional file-based video recording format.

DVB[edit]

Application-specific restrictions on MPEG-2 video in the DVB standard:

Allowed resolutions for SDTV:

  • 720, 640, 544, 528, 480 or 352 × 480 pixel, 24/1.001, 24, 30/1.001 or 30 frame/s
  • 352 × 240 pixel, 24/1.001, 24, 30/1.001 or 30 frame/s
  • 720, 704, 544, 528, 480 or 352 × 576 pixel, 25 frame/s
  • 352 × 288 pixel, 25 frame/s

For HDTV:

  • 720 x 576 x 50 frame/s progressive (576p50)
  • 1280 x 720 x 25 or 50 frame/s progressive (720p50)
  • 1440 or 1920 x 1080 x 25 frame/s progressive (1080p25 = film mode)
  • 1440 or 1920 x 1080 x 25 frame/s interlace (1080i50)

ATSC[edit]

Main article: ATSC standards

The ATSC A/53 standard used in the United States, uses MPEG-2 video at the Main Profile @ High Level (MP@HL), with additional restrictions such as the maximum bitrate of 19.4 Mbit/s for broadcast television and 38.8 Mbit/s for cable television, 4:2:0 chroma subsampling format, and mandatory colorimetry information.

ATSC allows the following video resolutions, aspect ratios, and frame/field rates:

  • 1920 × 1080 pixel (16:9, square pixels), at 30p, 29.97p, 24p, 23.976p, 60i, 59.94i.
  • 1280 × 720 pixel (16:9, square pixels), at 60p, 59.94p, 30p, 29.97p, 24p, or 23.976p
  • 704 × 480 pixel (4:3 or 16:9, non-square pixels), at 60p, 59.94p, 30p, 29.97p, 24p, 23.976p, 60i, or 59.94i
  • 640 × 480 pixel (4:3, square pixels), at 60p, 59.94p, 30p, 29.97p, 24p, 23.976p, 60i, or 59.94i

ATSC standard A/63 defines additional resolutions and aspect rates for 50 Hz (PAL) signal.

The ATSC specification and MPEG-2 allow the use of progressive frames, even within an interlaced video sequence. For example, a station that transmits 1080i60 video sequence can use a coding method where those 60 fields are coded with 24 progressive frames and metadata instructs the decoder to interlace them and perform 3:2 pulldown before display. This allows broadcasters to switch between 60 Hz interlaced (news, soap operas) and 24 Hz progressive (prime-time) content without ending the MPEG-2 sequence and introducing a several seconds of delay as the TV switches formats. This is the reason why 1080p30 and 1080p24 sequences allowed by the ATSC specification are not used in practice.

The 1080-line formats are encoded with 1920 × 1088 pixel luma matrices and 960 × 540 chroma matrices, but the last 8 lines are discarded by the MPEG-2 decoding and display process.

ATSC A/72 is the newest revision of ATSC standards for digital television, which allows the use of H.264/AVC codec and 1080p60 signal.

MPEG-2 audio was a contender for the ATSC standard during the DTV "Grand Alliance" shootout, but lost out to Dolby AC-3.

ISDB-T[edit]

Technical features of MPEG-2 in ATSC are also valid for ISDB-T, except that in the main TS has aggregated a second program for mobile devices compressed in MPEG-4 H.264 AVC for video and AAC-LC for audio, mainly known as 1seg.

Patent pool[edit]

MPEG LA, a private patent licensing organization, has acquired rights from over 20 corporations and one university to license a patent pool of approximately 640 worldwide patents, which it claims are the "essential" to use of MPEG-2 technology, although many of the patents have since expired.[30][31] Where software patentability is upheld, the use of MPEG-2 requires the payment of licensing fees to the patent holders. Other patents are licensed by Audio MPEG, Inc.[32] The development of the standard itself took less time than the patent negotiations.[33][34] Patent pooling between essential and peripheral patent holders in the MPEG-2 pool is the subject of a study by the University of Wisconsin.[35] Over half of the patents expired in 2012.[36]

According to the MPEG-2 licensing agreement any use of MPEG-2 technology is subject to royalties.[37] MPEG-2 encoders are subject to a royalty of $2.00 per unit, decoders are subject to a royalty of $2.00 per unit, and royalty-based sales of encoders and decoders are subject to different rules and $2.50 per unit.[37] Also, any packaged medium (DVDs/Data Streams) is subject to licence fees according to length of recording/broadcast.[37] A criticism of the MPEG-2 patent pool is that even though the number of patents will decrease from 1,048 to 416 by June 2013 the license fee has not decreased with the expiration rate of MPEG-2 patents.[38][39][40][41] Since January 1, 2010, the MPEG-2 patent pool has remained at $2 for a decoding license and $2 for an encoding license.[37][39][40] By 2015 more than 90% of the MPEG-2 patents will have expired but as long as there are one or more active patents in the MPEG-2 patent pool in either the country of manufacture or the country of sale the MPEG-2 license agreement requires that licensees pay a license fee that does not change based on the number of patents that have expired.[37][38][39][40][41]

Patents (U.S. only)[edit]

See also[edit]

References[edit]

  1. ^ ISO/IEC 13818 MPEG-2 at the ISO Store.
  2. ^ a b ITU-T. "H.222.0 : Information technology - Generic coding of moving pictures and associated audio information: Systems". Retrieved 2010-06-03. 
  3. ^ ITU-T (May 2006). "H.222.0 Summary". Retrieved 2010-06-03. 
  4. ^ SMPTE Registration Authority, LLC - registration authority for MPEG-2 format identifiers Retrieved on 2009-07-06
  5. ^ "H.262 : Information technology - Generic coding of moving pictures and associated audio information: Video". ITU-T Website. International Telecommunication Union - Telecommunication Standardization Sector (ITU-T). February 2000. Retrieved 2009-08-13. 
  6. ^ a b D. Thom, H. Purnhagen, and the MPEG Audio Subgroup (October 1998). "MPEG Audio FAQ Version 9 - MPEG Audio". Retrieved 2009-10-31. 
  7. ^ a b c d ISO (October 1998). "MPEG Audio FAQ Version 9 - MPEG-1 and MPEG-2 BC". ISO. Retrieved 2009-10-28. 
  8. ^ a b c d MPEG.ORG. "AAC". Retrieved 2009-10-28. 
  9. ^ a b ISO (2006-01-15), ISO/IEC 13818-7, Fourth edition, Part 7 - Advanced Audio Coding (AAC) (PDF), retrieved 2009-10-28 
  10. ^ ISO (2004-10-15), ISO/IEC 13818-7, Third edition, Part 7 - Advanced Audio Coding (AAC) (PDF), retrieved 2009-10-19 
  11. ^ a b Werner Oomen, Leon van de Kerkhof. "MPEG-2 Audio Layer I/II". chiariglione.org. Retrieved 2009-12-29. 
  12. ^ Predrag Supurovic, MPEG Audio Frame Header, Retrieved on 2009-07-11
  13. ^ ISO (March 1996). "Florence Press Release". ISO. Retrieved 2009-10-28. 
  14. ^ MPEG. "MPEG standards". chiariglione.org. Retrieved 2014-07-24. 
  15. ^ ISO. "ISO/IEC JTC 1/SC 29 - Coding of audio, picture, multimedia and hypermedia information". Retrieved 2014-07-24. 
  16. ^ ISO. "ISO/IEC 13818-1:2013/Amd 1:2014, Extensions for simplified carriage of MPEG-4 over MPEG-2". Retrieved 2014-07-24. 
  17. ^ ISO. "ISO/IEC 13818-1:2013/Amd 2:2014 - Signalling of transport files, signalling MVC view association to eye and MIME type registration". Retrieved 2014-07-24. 
  18. ^ ISO. "ISO/IEC 13818-1:2013/Amd 3:2014 - Transport of HEVC video over MPEG-2 systems". Retrieved 2014-07-24. 
  19. ^ ISO. "ISO/IEC 13818-1:2013/Amd 4:2014 - Support for event signalling in Transport Stream in MPEG-2 systems". Retrieved 2014-07-24. 
  20. ^ ISO. "ISO/IEC 13818-4:2004/Amd 3:2009". Retrieved 2009-10-29. 
  21. ^ ISO. "ISO/IEC 13818-6:1998/Amd 3:2001". Retrieved 2009-10-29. 
  22. ^ MPEG (1997-02-21). "DSM-CC FAQ Version 1.0". MPEG. Retrieved 2010-08-01. 
  23. ^ IEEE (1996). "An Introduction to Digital Storage Media - Command and Control (DSM-CC)". MPEG. Retrieved 2010-08-01. 
  24. ^ ISO. "ISO/IEC 13818-7:2006/Amd 1:2007, Transport of MPEG Surround in AAC". Retrieved 2009-10-29. 
  25. ^ chiariglione.org (2010-02-04). "Riding the Media Bits, The development of MPEG-2 - Part A". Retrieved 2010-02-09. 
  26. ^ chiariglione.org (October 2000). "Short MPEG-2 description". Retrieved 2009-10-31. 
  27. ^ "MPEG Intellectual Property Management and Protection". MPEG. April 2009. Retrieved 2010-08-01. 
  28. ^ IPMP in MPEG – W3C DRM workshop 22/23 January 2001 (PPT), retrieved 2010-08-01 
  29. ^ ISO. "ISO/IEC 23001-3:2008, Information technology -- MPEG systems technologies -- Part 3: XML IPMP messages". Retrieved 2009-10-29. 
  30. ^ Mpeg La
  31. ^ audioMPEG.com - - - US Patents
  32. ^ audioMPEG.com - - - patent management and licensing company specializing in the licensing of audio technology
  33. ^ Richard M Stallman, Patents - Barriers to development Theora Video and Vorbis Audio
  34. ^ [1]
  35. ^ Quint, Dan; Amit Gandhi. "Economics of Patent Pools When Some (but not all) Patents are Essential". Working Paper. Retrieved 2009-10-11. 
  36. ^ Rob Glidden, Half of MPEG-2 Patents Expire in 2012, December 8, 2011
  37. ^ a b c d e "MPEG-2 License Agreement". MPEG LA. 2013-05-13. Retrieved 2013-05-19. 
  38. ^ a b "Patent Pools May Create Anticompetitive Effects, New Report Finds". Business Wire. 2013-05-09. Retrieved 2013-06-06. 
  39. ^ a b c Steve Pociask (2013-05-13). "Consumer tech rip-off from patent pools". The Daily Caller. Retrieved 2013-05-19. 
  40. ^ a b c Bret Swanson (2013-04-30). "MPEG-LA Shows Need to Rebuild IP Foundations". Forbes. Retrieved 2013-05-19. 
  41. ^ a b Steve Forbes (2013-03-18). "America's patent system is all wrong for today’s high-tech world". Fox News Channel. Retrieved 2013-06-05. 
  42. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4833543
  43. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4970590
  44. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5453790
  45. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5136377
  46. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4383272
  47. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5291284
  48. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4982270
  49. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5068724
  50. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5091782
  51. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5093720
  52. ^ a b http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=RE35093
  53. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4796087
  54. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5235618
  55. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4706260
  56. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4813056
  57. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4394774
  58. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4698672
  59. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5426464
  60. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5486864
  61. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5491516
  62. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5600376
  63. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5796743
  64. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5867501
  65. ^ a b http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4849812
  66. ^ a b http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4901075
  67. ^ a b http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5021879
  68. ^ a b http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5027206
  69. ^ a b http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5128758
  70. ^ a b http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5179442
  71. ^ a b http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5333135
  72. ^ a b http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5606539
  73. ^ a b http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5608697
  74. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5699476
  75. ^ a b http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5740310
  76. ^ a b http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5844867
  77. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=6181712
  78. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=6792001
  79. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=RE37057
  80. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=RE37568
  81. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5113255
  82. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=RE35910
  83. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=RE36015
  84. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=RE36507
  85. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=RE39276
  86. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=RE39278
  87. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=RE39280
  88. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5223949
  89. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5412430
  90. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5784107
  91. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4954892
  92. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5072295
  93. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5268846
  94. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5949489
  95. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5963258
  96. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5970175
  97. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5990960
  98. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=6002439
  99. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=6097759
  100. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=6188794
  101. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=6307973
  102. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7362805
  103. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7376184
  104. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7756202
  105. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7936817
  106. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4958226
  107. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5227878
  108. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5500678
  109. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5563593
  110. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5461421
  111. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5467086
  112. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5654706
  113. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=6680975
  114. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7292657
  115. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7609760
  116. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7616687
  117. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7684490
  118. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7724821
  119. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7724822
  120. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7724823
  121. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7724824
  122. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7724828
  123. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7724829
  124. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7742522
  125. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7742527
  126. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7764735
  127. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7782956
  128. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7787538
  129. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5418782
  130. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5420866
  131. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5457701
  132. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4864393
  133. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=RE37222
  134. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5191436
  135. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5291486
  136. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5298991
  137. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5343248
  138. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5428396
  139. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5461420
  140. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5481553
  141. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5510840
  142. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5539466
  143. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5543847
  144. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5559557
  145. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5663763
  146. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5666461
  147. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5701164
  148. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5946042
  149. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5982437
  150. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=6040863
  151. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=6160849
  152. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7627041
  153. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4800432
  154. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4969055
  155. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5289276
  156. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5365272
  157. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5381181
  158. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5422676
  159. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5442400
  160. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5459789
  161. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5483287
  162. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5565923
  163. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5784110
  164. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7020204
  165. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=7334248
  166. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5317397
  167. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5424779
  168. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5467136
  169. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5742344
  170. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5986713
  171. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=RE34965
  172. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=RE35158
  173. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=RE36822
  174. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5103307
  175. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5175618
  176. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5341457
  177. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=RE39080
  178. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4972484
  179. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5214678
  180. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5323396
  181. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5539829
  182. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5606618
  183. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5530655
  184. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5777992
  185. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=6289308
  186. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5481643
  187. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5544247
  188. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5610985
  189. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5740317
  190. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5878080
  191. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5960037
  192. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5991715
  193. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=6023490
  194. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4821260
  195. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=4942607
  196. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5214742
  197. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5227990
  198. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5384811
  199. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5736943
  200. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5455833
  201. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5559834
  202. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5321729
  203. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5706309
  204. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5701346
  205. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5742735
  206. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5812672
  207. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5579430
  208. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=6185539
  209. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=6009399
  210. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5924060
  211. ^ http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5703999

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