ITIS 1210 Introduction to WebBased Information Systems Chapter
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 § MP 3 § 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 § Real. Player § Music. Match Jukebox § i. Tunes
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 k. Hz § CD: 44 k. Hz § 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 25 MB § 210, 000 bits § Over a 56 K modem – about an hour!
Video § Frame rate § TV: 30 frames per second (fps) § Web: 12 -15 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: § Real. Audio § Quick. Time § Windows Media § Problem § Sound quality generally not as good as a CD
Real. Player Streaming § Browser link to Real. Player file § Does not go to the actual file § Links to a Real. Player 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
Real. Player Streaming § Metafile launches the Real. Player software § Real. Player § Contacts the URL found in the metafile § URL points to a Real. Player server § Not a regular Web server § Specifically designed to deliver Real. Player data
Real. Player Streaming § Real. Player 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
Real. Player 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
Real. Player Streaming § Packets arrive at user and are stored in a buffer § When buffer is full the packets are sent to the Real. Player player § While data from the buffer is being played, more data is being loaded from the Real. Player server
Real. Player Streaming § User can jump ahead (or back) in the file § Real. Player may pause while re-loading the buffer § Contacting Real. Player site to get fresh set of packets
MP 3 § Uses special compression algorithm § Shrinks file size § Retains CD-like music quality § Process begins by recording the music § Same as normal recording § Special MP 3 software (ripper) § Converts to MP 3 format § File size typically <= 3 MB
MP 3 § MP 3 file posted on Internet § You visit the MP 3 site and download the file § Played using a special player § Portable (i. POD) § On regular PC § Can also be streamed
MP 3 § Major problem with copyright infringement § Many MP 3 files created without original artists permission § Can be downloaded to an MP 3 player § Internal memory § Memory card § Erased and replaced § i. Pod 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 § Real. Player (www. realplayer. com) § Windows Media Player (www. microsoft. com) § Stored on a Web server § www. musicmatch. com § 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
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