MPEG-4

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MPEG-4 is an MPEG standard ( ISO / IEC -14496) that describes methods for video and audio data compression , among other things . Originally, the goal of MPEG-4 was to support systems with low resources or narrow bandwidths (mobile phones, video telephones, ...) with relatively little loss of quality. Since H.263 , an ITU standard for video decoding and compression, had already met these requirements satisfactorily, it was integrated into MPEG-4 as part 2 without major changes .

By mid-2019, almost all patents in part 2 have expired, so that this can soon be used without a license. Three patents are still valid in Germany (until 2021).

In addition to video decoding, some audio standards, such as Advanced Audio Coding (AAC) , which is already standardized in MPEG-2, and support for digital rights management , which is known as Intellectual Property Management and Protection (IPMP), have also been included in the standard.

The official container format of MPEG-4 is MP4 .

MPEG-4 parts

MPEG-4 is composed of a plurality of standards, the parts ( English parts are) called, including the following:

  • Part 1 (ISO / IEC 14496-1): Systems
  • Part 2 (ISO / IEC 14496-2): Visual. These include the well-known MPEG-4 codecs DivX and Xvid. One of the many profiles in Part 2 is the Advanced Simple Profile (ASP).
  • Part 3 (ISO / IEC 14496-3): Audio. Contains the descriptions of Advanced Audio Coding (including HE-AAC ), Audio Lossless Coding , Scalable to Lossless , Direct Stream Transfer , CELP , HVXC and TwinVQ .
  • Part 4 (ISO / IEC 14496-4): Conformance
  • Part 5 (ISO / IEC 14496-5): Reference Software
  • Part 6 (ISO / IEC 14496-6): Delivery Multimedia Integration Framework (DMIF).
  • Part 7 (ISO / IEC 14496-7): Optimized Reference Software
  • Part 8 (ISO / IEC 14496-8): Carriage on IP networks
  • Part 9 (ISO / IEC 14496-9): Reference Hardware
  • Part 10 (ISO / IEC 14496-10): Advanced Video Coding (AVC). A codec for video signals that is technically identical to the ITU-T's H.264 standard .
  • Part 11 (ISO / IEC 14496-11): Scene description ( BIFS ) and Application engine ( MPEG-J )
  • Part 12 (ISO / IEC 14496-12): ISO Base Media File Format. Contains the description of the Quicktime container format .
  • Part 13 (ISO / IEC 14496-13): Intellectual Property Management and Protection (IPMP) Extensions
  • Part 14 (ISO / IEC 14496-14): MPEG-4 File Format ( MP4 ). Container format for MPEG-4 content, based on Part 12.
  • Part 15 (ISO / IEC 14496-15): AVC File Format. Container format for part 10 videos based on part 12
  • Part 16 (ISO / IEC 14496-16): Animation Framework eXtension (AFX)
  • Part 17 (ISO / IEC 14496-17): Timed Text subtitle format
  • Part 18 (ISO / IEC 14496-18): Font Compression and Streaming (for OpenType fonts)
  • Part 19 (ISO / IEC 14496-19): Synthesized Texture Stream
  • Part 20 (ISO / IEC 14496-20): Lightweight Scene Representation (LASeR)
  • Part 21 (ISO / IEC 14496-21): MPEG-J Graphical Framework eXtension (GFX)
  • Part 22 (ISO / IEC 14496-22): Open Font Format Specification (OFFS), based on OpenType
  • Part 23 (ISO / IEC 14496-23): Symbolic Music Representation (SMR)
  • Part 24 (ISO / IEC 14496-24): Audio and systems interaction
  • Part 25 (ISO / IEC 14496-25): 3D Graphics Compression Model
  • Part 26 (ISO / IEC 14496-26): Audio Conformance (not yet finished)
  • Part 27 (ISO / IEC 14496-27): 3D Graphics Conformance (not finished yet)
  • Part 28 (ISO / IEC 14496-28): Composite Font (not finished yet)
  • Part 29 (ISO / IEC 14496-29): Web Video Coding (not finished yet)
  • Part 30 (ISO / IEC 14496-30): Timed text (and Other Visual Overlays) and associated images in ISO Base Media File Format (not yet finished)
  • Part 31 (ISO / IEC 14496-31): Video Coding for Browsers (not finished yet)

(As of July 2014).

Profiles are also defined within the parts, so the implementation of a part is usually not an implementation of the whole part.

Video decoding

For the Advanced Simple Profile (ASP) , the decoder part for global motion compensation can simply be left out.

Block diagram of a decoder for MPEG-4 Advanced Simple Profile (ASP)

Variable length decoding

The variable length decoding (VLC) is based on the Huffman procedure for redundancy reduction . The code words are decoded with the help of tables, so-called “look-up tables”.

Inverse scanning

A one-dimensional data field QFS [ n ] with values ​​from 0 to 63 for n is obtained from the variable length decoding . This output is converted at this point into a two-dimensional data field with the identifier from the block diagram above PQF [ v ] [ u ], where v and u assume values ​​from 0 to 7. The following figure shows the three defined patterns for scanning.

a) "alternate-horizontal" - b) "alternate-vertical" - c) "zigzag" scanning

Inverse DC and AC prediction

This adaptive selection of DC and AC prediction directions is based on a comparison of the horizontal and vertical DC gradients around the block to be decoded.

Inverse quantization

The quantization process itself is reversible and therefore a redundancy-reducing method. However, a limited number of discrete values are available for the reconstruction of the DCT coefficients . Thus the inverse quantization is lossy. The two advantages of the quantization process are:

  1. Coefficients that are significant for the viewer, i.e. those that make a significant contribution to maintaining the quality of the image, are retained despite the slight deviation. Insignificant coefficients are deleted. Typically, this results in the majority of the 64 coefficients in the 8 × 8 matrix being zero after the inverse quantization.
  2. A sparse matrix with a limited number of discrete values ​​can be compressed efficiently.

Inverse Discrete Cosine Transformation

The Inverse Discrete Cosine Transformation (IDCT) is a method for irrelevance reduction .

Well-known codec implementations (MPEG-4 codecs)

Video
DivX
Xvid
HDX4
3ivx
FFmpeg contains a native MPEG-4 ASP video encoder and decoder as well as an H.264 decoder
x264 open source encoder for H.264
Nero Digital Video (ASP, H.264)
Apple QuickTime (MPEG-4 Video, H.263, H.264)
Audio
Psytel AAC, the predecessor of Nero AAC
FAAC, an AAC encoder and FAAD2, an open source decoder
FFmpeg supports the decoding and - experimentally - the encoding of AAC and contains an ALS decoder
Systems (BIFS)
GPAC Project on Advanced Content, BIFS player, encoder and authoring tools for interactive MPEG-4 content

transport

The transport is called “Delivery Multimedia Integration Framework” in MPEG-4. The function is to hide the actual source of the multimedia data streams so that the player on the terminal (possibly PC) is independent of the transport network. The following are standardized possible scenarios:

  • locally (e.g. on the local hard drive)
  • remote-interactive (client-server application, such as video on demand)
  • broadcast (unidirectional reception of data streams).

For the local case, the file format is standardized as “ISO Base Media File Format” in MPEG-4 Part 12. The Apple company made the first source code available in 1998. The MP4 file format in Part 14 of the standard was built and developed on this basis.

Reference software

  • Implementation Model 1 (IM1)
  • IM1 - 2D

See also

literature

  • Klaus Diepold, Sebastian Moeritz: Understanding MPEG-4. (Technology and Business Insights). Focal, Oxford 2005, ISBN 0-240-80594-1 .
  • Uwe Kühhirt, Marco Rittermann: Interactive audiovisual media (MPEG-4 multimedia systems. Audiovisual 2-D and 3-D scenes. Natural media objects. Synthetic media objects. Interactions. Digital media chain). Fachbuchverlag Leipzig in Carl Hanser Verlag, Munich 2007, ISBN 978-3-446-40300-0 .
  • Fernando Pereira, Touradj Ebrahimi (Ed.): The MPEG-4 Book. Prentice Hall, Upper Saddle River NJ 2002, ISBN 0-130-61621-4 .
  • Iain EG Richardson: H.264 and MPEG-4 Video Compression. Video Coding for Next-Generation Multimedia. Reprinted edition. Wiley, Chichester et al. 2008, ISBN 978-0-470-84837-1 .
  • Tilo Strutz: Image data compression. Basics, coding, wavelets, JPEG, MPEG, H.264 4th, revised and supplemented edition. Vieweg + Teubner, Wiesbaden 2009, ISBN 978-3-8348-0472-3 .
  • Aaron E. Walsh, Mikaël Bourges-Sévenier: MPEG-4 Jump-Start. Prentice Hall, Upper Saddle River NJ 2002, ISBN 0-130-60036-9 .
  • Wolfgang Wunderlich: Digital television HDTV, HDV, AVCHD for beginners and those switching. Auberge-TV-Verlag, La Vega DC 2007, ISBN 978-3-00-023484-2 .

Web links

Individual evidence

  1. ↑ MPEG-4 Visual Attachment 1 - as of April 2020, patents still valid in Germany:
    • DE: 501 03 996.1 (EP: 01 94 0135.5): “Method and device for storing and processing image information of images that follow one another in time”, Siemens AG
    • DE: 101 43 063.9 : "Procedure for reducing header information", Siemens AG
    • DE: 601 45 600.9 (EP: 01 90 7562.1): “Re-synchronization method for video decoding”, Koninklijke Philips NV