ITIS 1210 Introduction to Web-Based Information Systems Chapter 36 How Music and Audio Work on the Internet

Introduction  Audio files  Digitized versions of sound  Variety of formats available  MP3  WAV  AU  Download then play  Requires special software  Tend to be quite large

Introduction  New computers typically have the appropriate software built in  Windows Media Player  RealPlayer  MusicMatch Jukebox  iTunes

Sound  Sound is continuous

Sound  Problem  Cannot express continuous data in a digital (discontinuous) medium  Instead, take a sample  Take a reading every so often  Record the reading at that point  Ignore data between readings (samples)

Sound

Sound  Sample rates  Telephone: 8 kHz  CD: 44 kHz  The data ends up being a long series of numbers  44,000 per second for a CD sound track

Sound  Problem – Lots of numbers take lots of time  1 CD track contains 25MB  210,000,000 bits  Over a 56K modem – about an hour!

Video  Frame rate  TV: 30 frames per second (fps)  Web: fps  Connection controls – cable/DSL vs. dial-up  Compression  Frame of 320 x 240 pixels = 76,000 pixels  1,228,000 bits at 16 bits per pixel  At 15 fps, one minute = 1,105,920,000 bits!

Sound  Solution: compress  Codec: compressor-decompressor  Algorithm used to:  Compress files before they are sent to user  Decompress them before they are played  Streaming – alternative to downloading  Sound is transmitted to user continuously instead of in a single file  Requires special server and user plug-in

Sound  Streaming choices:  RealAudio  QuickTime  Windows Media  Problem  Sound quality generally not as good as a CD

RealPlayer Streaming  Browser link to RealPlayer file  Does not go to the actual file  Links to a RealPlayer metafile on a special server  Sent back to your PC  Metafile contains  Links to the actual sound file location (URL)  Instructions to browser on how to play the file

RealPlayer Streaming  Metafile launches the RealPlayer software  RealPlayer  Contacts the URL found in the metafile  URL points to a RealPlayer server  Not a regular Web server  Specifically designed to deliver RealPlayer data

RealPlayer Streaming  RealPlayer software and server  Communicate with each other  User’s Internet connection speed  If slow  A small, lower quality file sent to user  If high  Larger, higher quality file sent

RealPlayer Streaming  Sound files are generally too large to be sent as is  Instead, they are compressed  IP packet sent using UDP  User Datagram Protocol  UDP does not replace packets lost in transmission  Sound player at user end would have to wait for the missing packet thus interrupting the audio

RealPlayer Streaming  Packets arrive at user and are stored in a buffer  When buffer is full the packets are sent to the RealPlayer player  While data from the buffer is being played, more data is being loaded from the RealPlayer server

RealPlayer Streaming  User can jump ahead (or back) in the file  RealPlayer may pause while re-loading the buffer  Contacting RealPlayer site to get fresh set of packets

MP3  Uses special compression algorithm  Shrinks file size  Retains CD-like music quality  Process begins by recording the music  Same as normal recording  Special MP3 software (ripper)  Converts to MP3 format  File size typically <= 3MB

MP3  MP3 file posted on Internet  You visit the MP3 site and download the file  Played using a special player  Portable (iPOD)  On regular PC  Can also be streamed

MP3  Major problem with copyright infringement  Many MP3 files created without original artists permission  Can be downloaded to an MP3 player  Internal memory  Memory card  Erased and replaced  iPod records to end of storage before reusing deleted space at beginning

Internet Broadcast Radio  Two main types  Traditional radio stations that have an Internet component  Internet-only stations  Content still virtually the same  Music  News  Talk

Internet Broadcast Radio  For Internet  Station’s content converted to a digital format  RealPlayer (  Windows Media Player (  Stored on a Web server   To listen,  Launch player  Select station from online list

Internet Broadcast Radio  Player software contacts server  Server sends data in a stream  Software plays streamed data as it is received  User controls like a radio  High-speed connection usually means better quality