The standards situation for multimedia is quite complex. On one hand it is a fast moving area, where some standards have been promoted but not accepted. Some standards are in preliminary phases, and after heavy investment, the might not end up with full acceptance.

On the other hand, because multimedia involves a lot of fields, standards for the different fields might be relevant. For example, the following incomplete list of multimedia standards, can give an idea of how many standards might be interesting for multimedia:

CCITT/ISO (now ITU – T) standards for multimedia include F.700, G.711, G.721, G.722, G.725, H.221, H.242, H.261, H.320, HyTime, IIF, JBIG, JPEG, MHEG, MPEG, ODA, T.80, X.400, G.723, G.726, G.727, G.728, G.764, G.765, H.200, H.241, H.243, T.120

Internet standards include IP Multicast, MIME, RTP, ST-2, RFC 741, Xv and mvex

W3C standards are also very relevant .

Proprietary standards are Bento, GIF, QuickTime, RIFF, DVI, MIDI.

Official standards follow a lengthy process, and thus usually standards are associated to a status which indicates the current situation in the process. Fon instance, phases of this process are: calls for contributions, committee draft (CD), draft of international standard (DIS), international standard (IS), etc. Internet (IETF) and W3C "standards" also follow their own process, with other terminology.

Unprocessed image and video in digital form occupy a huge amount of space, at least when compared to text. A character is usually one byte and a page will be several hundreds of them. A colour image of the size of a small standard VGA screen occupies, in principle, 640x480x3 bytes, i.e., the number of pixels multiplied by the number of bytes per pixel (one for each of the R, G, and B channels).

It is extremely important to reduce this size for storage and transmission purposes. This is achieved through coding the image in a compressed way at one end, and decoding it to an uncompressed form at the other side. For this process to be useful it is important its standardization.

Thus, image and video compression standards quickly appeared for transmission. For example, H.261 and H.263 are image standards for videotelephony. Both of them work at 64 Mbits/sec (the speed of transmission is a very important parameter), while H.261 can also work at 2 Mbauds, offering the possibility of better quality videotelephony. The H.* have associated with them some G.* standards for the audio component of the video.

JPEG

JPEG stands for Joint Photographic Experts Group, the original name of the committee that wrote the standard. Now the body is officially called ITU – T JTC1/SC2/WG10.

JPEG is a lossy compression scheme, meaning that the decompressed image is usually worse than the original: some losses exist in the proces. Nevertheless, JPEG exploits known characteristics of the human eye to achieve a very high degree of compression, without much apparent visual degradation.

The compression parameters can be adjusted by the user, trading off file size against output image quality. The basic ideas behind the compression scheme are explained later.

A new version called JPEG2000 has recently become an official standard. It is based on wavelet transforms, and the applications are more ambitious than for the original JPEG.

MPEG 1, 2, 3

MPEG stands for Moving Pictures Expert Group, which is the popular name of the ISO/IEC committee working on digital colour video and audio compression, ITU – T JTC1/SC2/WG11, established in 1988.

According to MPEG home page, the group is "in charge of the development of standards for coded representation of digital audio and video". MPEG has produced:

MPEG-1, a standard for storage and retrieval of moving pictures and audio on storage media (approved November 1992); products such as Video CD and MP3 are based on it MPEG-2, a standard for digital television (approved November 1994); Digital Television set top boxes and DVD are based on it MPEG-4 version 1 and 2, a standard for multimedia applications (approved October 1998 and December 1999, respectively), for the fixed and mobile web MPEG-7 a content representation standard for multimedia information search, filtering, management and processing

MPEG-1

The specific target of MPEG-1 is CD-ROM and DAT platforms for multimedia applications with a bandwidth of 1.5 Mbit/sec. The three parts of the standard are video encoding, with a binary stream taking almost the 1.15 Mbit/s bandwidth, audio encoding, and systems (which includes information for synchronization and information about the coding). The target quality of MPEG-1 is that of a VHS video.

Although MPEG-1 can cater for other possibilities, the basic parameters for video use a non-interlaced format, 352 x 240 pixels x 30 frames/s in the US; 352 x 288 x 25 frames/s in Europe (CIF). The RGB pixel information is converted into Y (luminance), and UV (chrominance); the chrominance is sub sampled. The compression scheme is based on the Discrete Cosine Transform (DCT), which is a variant of the Fourier Transform, performed on 8x8 blocks of the image.

Quantization and Huffman coding are also used following this step. The compression also uses the redundancy in time by means of motion vectors. The coding scheme distinguishes three types of frames: I (intra) frames, which are coded as still images; P (predicted) frames, which are deltas from the most recent past I or P frame; and B (bidirectional) frames, which are interpolations between I and P frames. I frames are sent once every 10 or 12 frames.

The scheme is asymmetric: a lot of computing power is required to encode, while decoding is less demanding. The 1986 version of JPEG is also DCT based, very similar to the coding we have described for MPEG-1.

MPEG-2 (and 3)

MPEG-2 is designed to offer higher quality than MPEG-1, at a higher bandwidth (between 4 and 10 Mbit/s). The scheme is very similar to MPEG-1, and scalable.

MPEG-3 was targetted for HDTV, but was never developed, as it was realised that one of the versions of MPEG-2 (the level High 1440) could be used for High Definition Television. But as this was realised later, the next forthcoming standard at the time was named MPEG-4.

By the way, it is worth remarking that the very popular MP3 is the audio part of the MPEG-2 standard.