Practical designed to transmit video and images over

Practical Activity 1 : Compression Methods – MPEGThe Moving Picture Experts Group ( MPEG ) is a group ofexperts that was formed by the International Organisation for Standardisation (ISO) and the International Electro technical Commission ( IEC) in 1988 andgiven the task to set the standards for audio and video compression. MPEGSofficial designation within these standards is ISO/IEC JTC 1/SC29/WG11 which isthe coding of audio, picture, multimedia and hypermedia information. MPEGusually hold four meeting per year in which approx 400 experts from variouscountries attend who are accredited by an appropriate National Standard body.These are mainly experts who have a stake in the digital audio, video andmultimedia industry. The convevor of the MPEG group is Leonardo Chiariglonealso kown as the father of MPEG started the group with about 15 experts oncompression technology.Below are the main MPEG standards currently in usetoday:MPEG-1: MPEG-1 Provides  a video resolution of 352-by-240 at 30 frames per second .This produces video quality slightly below the quality of a VCR.

MPEG-2: Offers resolutions of 720×480 and 1280×720 at 60 fps. This frame rate is sufficient for all the major TV standards including  high definition TV. MPEG-2 is used by DVD-ROMs. MPEG-2 can compress a 2 hour video into a few gigabytes. MPEG-3: Initially designed for HDTV MPEG-3 was abandoned in place of using MPEG-2 for HDTV.MPEG-4: A graphics and video compression algorithm standard that is based on MPEG-1 and MPEG-2 and Apple QuickTime technology. MPEG-4 files are designed to transmit video and images over a narrower bandwidth and can mix video with text, graphics and 2-D and 3-D animation layers. MPEG-4 was standardized by the ISO/IEC in October 1998.

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MPEG-7:  MPEG-7 provides a tool set for completely describing multimedia content. MPEG-7 is designed to be generic and not targeted to a specific application.MPEG-21: MPEG-21 describes a standard that defines the description of content and also processes for accessing, searching, storing and protecting the copyrights of content. MPEG-21 is geared toward resources that are offered, modified, sold, consumed, delivered, regulated or facilitated, including audio, video and images.MPEGis designed for video and audio files and its purpose is to compress thesefiles primarily for two reasons1.

       To save storage space ( a compressed audio or videofile can be drastically smaller than its original size therefore saving a greatdeal of storage space on a device)2.       To save on bandwidth in communication which savestime when sending data ( the smaller the size of a frame or packet this saveson transmission time)MPEG has gained a wide audience across the globerapidly. It has been adopted by leading multimedia technology firms likePhilips, Samsung, Intel, and Sony for their products.

The National Academy of Television Arts andSciences (NATAS) awarded its 1995-1996 Engineering Emmy for OutstandingAchievement in Technological Development to ISO/IEC for the development of theMPEG and JPEG standards. It was a recognition of the MPEG compressiontechnology as a cost-effective means of delivering high quality audio and videoprogramming to consumers by reducing the bandwidth necessary to carry thesignal to homes and businesses across the globe. As below wecan see the relevance and domination of the MPEG format today:Today’s computer systems are already supporting MPEG-1 audio and video. MPEG encoded files are available from a growing number of platforms, including CD-ROM and the Internet.MPEG-2 is the video standard for DVD players.

For DVD multichannel audio, MPEG-2 is the standard audio format for PAL/SECAM countries, and an option for NTSC countries.An increasing number of broadcasting applications are based on MPEG technology, e.g. DSS (Digital Satellite System), DAB (Digital Audio Broadcast), DVB (Digital Video Broadcast), ADR (Astra Digital Radio), Satellite feeds to cable networks, etc.MPEG is used over wan connections to provide very high quality video conferencing and general streaming for websites such as you tube and social media platforms.MPEG formatsand purposes :MPEG-1: Designed to producereasonable quality images and sound at low bit rates. MPEG-1 was designed tofit the bandwidth of CD-ROM and Video-CD and to run at at 352×240 pixels NTSC at 1.

5 megabits(Mbits) per second, a quality level about on par with VHS. MPEG-1 can also beencoded at bit rates as high as 4-5Mbits/sec. MPEG-1 is also used to transmit video over telephone networks such asAsymmetrical Digital Subscriber Lines ( DSL) for video conferencing . MPEG-2: Designed to produce higher quality images at higherbit rates between 3-10Mbits/sec, MPEG-2 at the full CCIR-601 resolution of720x486 pixels.

Its purpose is to provide true broadcast quality video and hasovercome MPEG-3 to be the standard for HDTV and DVD. The primary users ofMPEG-2 are broadcast and cable companies who demand broadcast quality digitalvideo and utilize satellite transponders and cable networks for delivery ofcable television and direct broadcast satellite. MPEG-3: Initially intended to be the standard for HDTVhowever MPEG-2 is now the preferred standard so MPEG-3 has been dropped. MPEG-4: Initially specified for very low bit rates but now itsupports up to 4Mbps. MPEG-4 is a big progression from MPEG-1 and MPEG-2providing additional services such as support for 2D and 3D and Coding at verylow rates (2 Kbit/s for speech, 5 Kbit/s for video) to very high ones (5 Mbit/sfor transparent quality Video, 64 Kbit/s per channel for CD quality Audio). Avery attractive addition however is the support it provides for the managementand protection of intellectual property and its ability to stream real timecontent. MPEG-7: This version is more associated with the contentitself, to allow a user friendly interface  Advantages of using MPEG: https://bytescout.

com/blog/2014/09/mp4-file-format.htmlSuitable for video streaming over the internet.Less loss of quality with higher degree of compression.Can store data types other than video and audio, such as objectdescriptors, scene descriptors and other object oriented file structures andMPEG features.Separate hint track is used to encode streaming information.MP4 files can be run virtually onall the major media players and sound card drivers Disadvantagesof using MPEG: https://www.

online-sciences.com/technology/video-container-formats-mpeg-mov-features-uses-cons-and-pros/ One drawback of this type of file is the softwarerequired to run, It is very proprietary, Each vendor has a different set ofbugs, As MPEGS are so compressed,they are not recommended for editing or archiving.MPEG does not feature some of theflexibilities of the other formats, making it a poor format for editing video, It is not editable, afinished file would have to be pre-edited and then re-encoded. How MPEG video compression works: https://bitdepth.thomasrutter.com/2010/02/02/how-jpeg-and-mpeg-picture-compression-algorithms-work/ All types of MPEG videos, work in a very similar way using block basedDCT image compression.

  This involves chopping up the picture into blocks,8 pixels by 8 pixels, and compressing each block separately, and using amathematical algorithm called a Discrete Cosine Transformation (DCT). Colour space conversionand resamplingIf necessary, theimage is first converted into the correct colour space and resolution. This involves separating the colour image into 3 separate images or ‘channels’:a luma channel which carries the brightness information (like a black and whiteimage), and two chroma channels which carry the colour information. Furthermore, the luma channel is usually given double or quadruple theresolution of the colour channels; this saves some storage space already, andworks because humans are much better at seeing intricate changes in lightnessthan colourSeparate into 8×8blocks and perform Discrete Cosine TransformEach channel of theimage is then divided into blocks of 8 pixels by 8 pixels (64 pixels perblock).  To each block, a mathematical formula called a Discrete CosineTransform (DCT) is performed.QuantisationQuantisation is theprocess of reducing the precision of a number so that it is less accurate, buttakes fewer bits to write to a device.

It works by dividing a number by acertain value, and throwing away the remainder. When multiplying by that valueagain in an attempt to get the original number, chances are that the number isclose to, but slightly different to, the number you started with.  Themore you divide the number by, the greater the strength of the quantisation andhence the greater the likely loss in precision once you multiple the numberagain.

The JPEG and MPEG compression can also apply different amounts ofquantisation to the different frequency coefficients within a single block, ordifferent amounts per block in an image.  When this is done, it is all inan attempt to get the best looking picture, as perceived by human eyes, for agiven amount of quantisation.MPEG video encoding can also involve motion estimation, wherea block can be optimised by only encoding the difference between it and anearby area of some other frame.

  Encoding is still done per-block, andthe blocks still undergo DCT and quantisation. Decoding the imageDecoding is areverse of the above process: the stream is decoded to find the coefficientsfor each block, and these coefficients are multiplied by the same number theywere previously divided by, in order to reverse the quantisation.

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