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Media communication standards

CP2022 - Lecture 9. Media communication standards. 1. Data types. Static and dynamic data Static data does not have a time element Usually a spatial relationship Text and Image Dynamic data has a time element Data is used in time sequence Audio and Video. 2. Text and image.

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Media communication standards

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  1. CP2022 - Lecture 9 Media communication standards 1

  2. Data types • Static and dynamic data • Static data does not have a time element • Usually a spatial relationship • Text and Image • Dynamic data has a time element • Data is used in time sequence • Audio and Video 2

  3. Text and image • Static formats - not time-related • No special communication needs • No particular communication standards • Used on the web as • ASCII (IA5) • GIF & JPEG 3

  4. Use of text • Text can be used in different ways on-line • Download - Browsing - Online reading • Depends on many factors • purpose, use, familiarity, application etc. 4

  5. Image • No real “standard” for communication • Image is usually data-intensive • Quality proportional to size (colour-depth) • Useful reductions gained by compression • Especially if • image detail is not critical • lossy compression is applicable 5

  6. Audio and Video • Dynamic communication -Time-related • Standards are related to telecoms (ITU) • Digital telephony and video telephony • Time relationship increases chances of compression (especially in video) • similar frames are redundant • similar waveforms are redundant 6

  7. Redundancy example • Audio consists of repetitive waves (sounds) • For example • Video consists of repetitive images 7

  8. Audio communication • Some “standards” are not standard • Most standards based on PCM or derivatives • Various efforts to improve compression • Good voice quality audio requires 64 kbps • 8 bit sample x 8000 Hz sample rate • Mobile telephones use compression to reduce this • Less data - lower quality 8

  9. Audio • MPEG compresses video and audio • uses filters and psycho-acoustic effects • MPEG audio has three layers of compression • MPEG Audio Layer 3 - MP3 • compresses CD quality sound at about 10:1 • gives near CD quality in 192 kbps • can be used at different compression rates and with different sample rates 9

  10. MPEG Audio Layers 10

  11. Audio communication • MP3 is widely used • on the Internet/WWW • on DCC (digital compact cassettes) • DAB (Digital audio broadcasting) 11

  12. Video Communication • MPEG is now common in video transmission (Digital TV) • but not on the Internet • H.261 is the International standard for video telephony • Based on 64 kbps channel size (ISDN) • H.261 compresses video • similar scheme to MPEG but • lower bit rates and lower quality 12

  13. H.261 13

  14. Brief details of H.261 • CIF and QCIF formats used • Macroblocks are “transformed” to reduce data • Colour sampling is at a lower rate than luminance (brightness) • Uses frame prediction similar to MPEG 14

  15. MHEG • MHEG is an “umbrella” standard for multimedia objects • The ISO standard for digital television • It provides a language for • control of delivery of multimedia objects • both local and distributed multimedia • uses other standards for components e.g. MPEG etc. 15

  16. Summary • Communication of any data requires standards • Multimedia objects require different standards depending on • static or dynamic data • amount of redundancy • quality issues • Standards are continually developing 16

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