MPEG-2

Key takeaways

MPEG-2 belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect MPEG-2 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of MPEG-2 from memory before moving on to harder problems.

Reference excerpt

MPEG-2 (a.k.a. H.222/H.262 as was defined by the ITU) is a standard for "the generic coding of moving pictures and associated audio information". 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/AVC and H.265/HEVC, backwards compatibility with existing hardware and software means it is still widely used, for example in over-the-air digital television broadcasting and in the DVD-Video standard.

Main characteristics 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, titled Information technology — Generic coding of moving pictures and associated audio information). 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

MPEG-2 Part 1 (ISO/IEC 13818-1 and ITU-T Rec. H.222.0), titled Systems, 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 with less overhead than transport stream. Program stream is designed for random access storage mediums such as hard disk drives, optical discs and flash memory. Transport stream file formats include M2TS, which is used on Blu-ray discs, AVCHD on re-writable DVDs and HDV on compact flash cards. Program stream files include VOB on DVDs and Enhanced VOB on the short lived HD DVD. The standard MPEG-2 transport stream contains packets of 188 bytes. M2TS prepends each packet with 4 bytes containing a 2-bit copy permission indicator and 30-bit timestamp. 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.

Video

MPEG-2 Part 2 (ISO/IEC 13818-2 and ITU-T Rec. H.262), titled Video, is similar to the previous MPEG-1 Part 2 standard, but adds 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 (CPB) limits. With some enhancements, MPEG-2 Video and Systems are also used in some HDTV transmission systems, and is the standard format for over-the-air ATSC digital television.

Audio MPEG-2 introduces new audio encoding methods compared to MPEG-1:

MPEG-2 Part 3

MPEG-2 Part 3 (ISO/IEC 13818-3), titled Audio, 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 with MPEG-1, allowing MPEG-1 audio decoders to decode the two main stereo components of the presentation. This extension is called MPEG Multichannel or MPEG-2 BC (backwards-compatible). MPEG-2 Part 3 also defines additional bit rates and sampling rates for MPEG-1 Audio Layers I, II, and III. This extension is known as MPEG-2 LSF (low sampling frequencies), since the new sampling rates are one-half multiples (16, 22.05 and 24 kHz) of the sampling rates defined in MPEG-1 (32, 44.1 and 48 kHz).

MPEG-2 Part 7

MPEG-2 Part 7 (ISO/IEC 13818-7), titled Advanced Audio Coding (AAC) specifies a rather different, non-backwards-compatible audio format. This format is most commonly called Advanced Audio Coding (AAC), but was originally called MPEG-2 NBC (non-backwards-compatible). AAC is more efficient than the previous MPEG audio standards, and is in some ways less complicated than its predecessor, MPEG-1 Part 3 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. AAC is also defined in MPEG-4 Part 3.

MPEG-2 Parts MPEG-2 standards are published as "Parts". Each part covers a certain aspect of the whole specification.

History MPEG-2 evolved out of the shortcomings of MPEG-1. MPEG-1's known weaknesses:

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Illustrations

Worked examples

Example 1 — a first encounter with MPEG-2

Start with the simplest possible case. Write down what MPEG-2 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to MPEG-2 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about MPEG-2 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of MPEG-2

In research: MPEG-2 appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses MPEG-2 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: MPEG-2 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Audio codecs, ISO/IEC standards, Interactive television, so understanding it makes those chapters shorter.
In everyday life: Look for MPEG-2 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study MPEG-2 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what MPEG-2 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain MPEG-2 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is MPEG-2 in simple terms?

MPEG-2 (a.k.a. H.222/H.262 as was defined by the ITU) is a standard for "the generic coding of moving pictures and associated audio information".

Why does MPEG-2 matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study MPEG-2?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on MPEG-2.