MPEG-1 is a standard for lossy compression of video and audio. It is designed to compress VHS-quality raw digital video and CD audio down to about 1.5 Mbit/s (26:1 and 6:1 compression ratios respectively) without excessive quality loss, making video CDs, digital cable/satellite TV and digital audio broadcasting (DAB) practical.
MPEG-1 has become a widely compatible lossy audio/video format, and is used in a large number of products and technologies. Perhaps the best-known part of the MPEG-1 standard is the first version of the MP3 audio format it introduced.
The MPEG-1 standard is published as ISO/IEC 11172, titled Information technology—Coding of moving pictures and associated audio for digital storage media at up to about 1.5 Mbit/s.
The standard consists of the following five Parts: Systems (defining a format for storage and synchronization of video, audio, and other data together in a single file—later dubbed the MPEG program stream to distinguish it from the MPEG transport stream format introduced as an alternative in MPEG-2). Video (compressed video content) Audio (compressed audio content), including MP3 and MP2 Conformance testing (testing the correctness of implementations of the standard) Reference software (example software showing how to encode and decode according to the standard)
History The predecessor of MPEG-1 for video coding was the H.261 standard produced by the CCITT (now known as the ITU-T). The basic architecture established in H.261 was the motion-compensated DCT hybrid video coding structure. It uses macroblocks of size 16×16 with block-based motion estimation in the encoder and motion compensation using encoder-selected motion vectors in the decoder, with residual difference coding using a discrete cosine transform (DCT) of size 8×8, scalar quantization, and variable-length codes (like Huffman codes) for entropy coding. H.261 was the first practical video coding standard, and all of its described design elements were also used in MPEG-1.
Modeled on the successful collaborative approach and the compression technologies developed by the Joint Photographic Experts Group and CCITT's Experts Group on Telephony (creators of the JPEG image compression standard and the H.261 standard for video conferencing respectively), the Moving Picture Experts Group (MPEG) working group was established in January 1988, by the initiative of Hiroshi Yasuda (Nippon Telegraph and Telephone) and Leonardo Chiariglione (CSELT). MPEG was formed to address the need for standard video and audio formats, and to build on H.261 to get better quality through the use of somewhat more complex encoding methods (e.g., supporting higher precision for motion vectors).
Development of the MPEG-1 standard began in May 1988. Fourteen video and fourteen 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 data rates of 1.5 Mbit/s. This specific bitrate was chosen for transmission over T-1/E-1 lines and as the approximate data rate of audio CDs. 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 in the process.
After 20 meetings of the full group in various cities around the world, and 4½ years of development and testing, the final standard (for parts 1–3) was approved in early November 1992 and published a few months later. The reported completion date of the MPEG-1 standard varies greatly: a largely complete draft standard was produced in September 1990, and from that point on, only minor changes were introduced. The draft standard was publicly available for purchase. The standard was finished with the 6 November 1992 meeting. The Berkeley Plateau Multimedia Research Group developed an MPEG-1 decoder in November 1992. A Continuous Media Player, Lawrence A. Rowe and Brian C. Smith, Proc. 3rd Int. Workshop on Network and OS Support for Digital Audio and Video, San Diego CA (November 1992) In July 1990, before the first draft of the MPEG-1 standard had even been written, work began on a second standard, MPEG-2, intended to extend MPEG-1 technology to provide full broadcast-quality video (as per CCIR 601) at high bitrates (3–15 Mbit/s) and support for interlaced video. Due in part to the similarity between the two codecs, the MPEG-2 standard includes full backwards compatibility with MPEG-1 video, so any MPEG-2 decoder can play MPEG-1 videos.
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 a reference implementation is provided in ISO/IEC-11172-5. 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. The first three parts (Systems, Video and Audio) of ISO/IEC 11172 were published in August 1993.
+MPEG-1 Parts Part Number First publicrelease date(first edition) latestcorrection Title Description Part 1 ISO/IEC 11172-1 1993 1999 Systems Part 2 ISO/IEC 11172-2 1993 2006 Video Part 3 ISO/IEC 11172-3 1993 1996 Audio Part 4 ISO/IEC 11172-4 1995 2007 Compliance testing Part 5 ISO/IEC TR 11172-5 1998 2007 Software simulation
Patents Due to its age, MPEG-1 is no longer covered by any essential patents and can thus be used without obtaining a licence or paying any fees. The ISO patent database lists one patent for ISO 11172, US 4,472,747, which expired in 2003. The near-complete draft of the MPEG-1 standard was publicly available as ISO CD 11172 by December 6, 1991. Reference 3 in the paper is to Committee Draft of Standard ISO/IEC 11172, December 6, 1991. Neither the July 2008 Kuro5hin article "Patent Status of MPEG-1, H.261 and MPEG-2", nor an August 2008 thread on the gstreamer-devel mailing list were able to list a single unexpired MPEG-1 Video and MPEG-1 Audio Layer I/II patent. A May 2009 discussion on the whatwg mailing list mentioned US 5,214,678 patent as possibly covering MPEG-1 Audio Layer II. Filed in 1990 and published in 1993, this patent is now expired.http://patft1.uspto.gov/netacgi/nph-Parser?patentnumber=5214678 "Digital transmission system using subband coding of a digital signal" Filed: May 31, 1990, Granted May 25, 1993, Expires May 31, 2010?
A full MPEG-1 decoder and encoder, with "Layer III audio", could not be implemented royalty free since there were companies that required patent fees for implementations of MPEG-1 Audio Layer III, as discussed in the MP3 article. All patents in the world connected to MP3 expired 30 December 2017, which makes this format totally free for use. On 23 April 2017, Fraunhofer IIS stopped charging for Technicolor's MP3 licensing program for certain MP3 related patents and software.
Former patent holders The following corporations filed declarations with ISO saying they held patents for the MPEG-1 Video (ISO/IEC-11172-2) format, although all such patents have since expired.
BBC Daimler Benz AG Fujitsu IBM Matsushita Electric Industrial Co., Ltd. Mitsubishi Electric NEC NHK Philips Pioneer Corporation Qualcomm Ricoh Sony Texas Instruments Thomson Multimedia Toppan Printing Toshiba Victor Company of Japan
Applications Most popular software for video playback includes MPEG-1 decoding, in addition to any other supported formats. The popularity of MP3 audio has established a massive installed base of hardware that can play back MPEG-1 Audio (all three layers). "Virtually all digital audio devices" can play back MPEG-1 Audio. Many millions have been sold to-date. Before MPEG-2 became widespread, many digital satellite/cable TV services used MPEG-1 exclusively. The widespread popularity of MPEG-2 with broadcasters means MPEG-1 is playable by most digital cable and satellite set-top boxes, and digital disc and tape players, due to backwards compatibility. MPEG-1 was used for full-screen video on Green Book CD-i, and on Video CD (VCD). The Super Video CD standard, based on VCD, uses MPEG-1 audio exclusively, as well as MPEG-2 video. The DVD-Video format uses MPEG-2 video primarily, but MPEG-1 support is explicitly defined in the standard. The DVD-Video standard originally required MPEG-1 Audio Layer II for PAL countries, but was changed to allow AC-3/Dolby Digital-only discs. MPEG-1 Audio Layer II is still allowed on DVDs, although newer extensions to the format, like MPEG Multichannel, are rarely supported. Most DVD players also support Video CD and MP3 CD playback, which use MPEG-1. The international Digital Video Broadcasting (DVB) standard primarily uses MPEG-1 Audio Layer II, and MPEG-2 video. The international Digital Audio Broadcasting (DAB) standard uses MPEG-1 Audio Layer II exclusively, due to its especially high quality, modest decoder performance requirements, and tolerance of errors. The Digital Compact Cassette uses PASC (Precision Adaptive Sub-band Coding) to encode its audio. PASC is an early version of MPEG-1 Audio Layer I with a fixed bit rate of 384 kilobits per second.
Part 1: Systems Part 1 of the MPEG-1 standard covers systems, and is defined in ISO/IEC-11172-1.
MPEG-1 Systems specifies the logical layout and methods used to store the encoded audio, video, and other data into a standard bitstream, and to maintain synchronization between the different contents. This file format is specifically designed for storage on media, and transmission over communication channels, that are considered relatively reliable. Only limited error protection is defined by the standard, and small errors in the bitstream may cause noticeable defects.
This structure was later named an MPEG program stream: "The MPEG-1 Systems design is essentially identical to the MPEG-2 Program Stream structure." This terminology is more popular, precise (differentiates it from an MPEG transport stream) and will be used here.
Elementary streams, packets, and clock references Elementary Streams (ES) are the raw bitstreams of MPEG-1 audio and video encoded data (output from an encoder). These files can be distributed on their own, such as is the case with MP3 files. Packetized Elementary Streams (PES) are elementary streams packetized into packets of variable lengths, i.e., divided ES into independent chunks where cyclic redundancy check (CRC) checksum was added to each packet for error detection. System Clock Reference (SCR) is a timing value stored in a 33-bit header of each PES, at a frequency/precision of 90 kHz, with an extra 9-bit extension that stores additional timing data with a precision of 27 MHz. These are inserted by the encoder, derived from the system time clock (STC). Simultaneously encoded audio and video streams will not have identical SCR values, however, due to buffering, encoding, jitter, and other delay.
Program streams
Program Streams (PS) are concerned with combining multiple packetized elementary streams (usually just one audio and video PES) into a single stream, ensuring simultaneous delivery, and maintaining synchronization. The PS structure is known as a multiplex, or a container format.
Presentation time stamps (PTS) exist in PS to correct the inevitable disparity between audio and video SCR values (time-base correction). 90 kHz PTS values in the PS header tell the decoder which video SCR values match which audio SCR values. PTS determines when to display a portion of an MPEG program, and is also used by the decoder to determine when data can be discarded from the buffer. Either video or audio will be delayed by the decoder until the corresponding segment of the other arrives and can be decoded.