1 CP Lecture 9 Media communication standards

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

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

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.

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

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

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

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

9 Audio MPEG compresses video and audio uses filters and psycho-acoustic effects MPEG audio has three layers of compression MP3 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

10 MPEG Audio Layers

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

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

13 H.261

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

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.

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