ITIS 1210ITIS 1210Introduction to Web-Based Introduction to Web-Based

Information SystemsInformation Systems

Chapter 36Chapter 36

How Music and Audio Work on the InternetHow Music and Audio Work on the Internet

IntroductionIntroduction

Audio filesAudio files Digitized versions of soundDigitized versions of sound Variety of formats availableVariety of formats available

MP3MP3 WAVWAV AUAU

Download then playDownload then play Requires special softwareRequires special software Tend to be quite largeTend to be quite large

IntroductionIntroduction

New computers typically have the New computers typically have the appropriate software built inappropriate software built in Windows Media PlayerWindows Media Player RealPlayerRealPlayer MusicMatch JukeboxMusicMatch Jukebox iTunesiTunes

SoundSound

Sound is continuousSound is continuous

SoundSound

ProblemProblem Cannot express continuous data in a digital Cannot express continuous data in a digital

(discontinuous) medium(discontinuous) medium

Instead, take a sampleInstead, take a sample Take a reading every so oftenTake a reading every so often Record the reading at that pointRecord the reading at that point Ignore data between readings (samples)Ignore data between readings (samples)

SoundSound

SoundSound

Sample ratesSample rates Telephone: 8 kHzTelephone: 8 kHz CD: 44 kHzCD: 44 kHz

The data ends up being a long series of The data ends up being a long series of numbersnumbers

44,000 per second for a CD sound track44,000 per second for a CD sound track

SoundSound

Problem – Lots of numbers take lots of Problem – Lots of numbers take lots of timetime

1 CD track contains 25MB1 CD track contains 25MB 210,000,000 bits210,000,000 bits Over a 56K modem – about an hour!Over a 56K modem – about an hour!

VideoVideo

Frame rateFrame rate TV: 30 frames per second (fps)TV: 30 frames per second (fps) Web: 12-15 fpsWeb: 12-15 fps Connection controls – cable/DSL vs. dial-upConnection controls – cable/DSL vs. dial-up

CompressionCompression Frame of 320 x 240 pixels = 76,000 pixelsFrame of 320 x 240 pixels = 76,000 pixels 1,228,000 bits at 16 bits per pixel1,228,000 bits at 16 bits per pixel At 15 fps, one minute = 1,105,920,000 bits!At 15 fps, one minute = 1,105,920,000 bits!

SoundSound

Solution: compressSolution: compress Codec: compressor-decompressorCodec: compressor-decompressor Algorithm used to:Algorithm used to:

Compress files before they are sent to userCompress files before they are sent to user Decompress them before they are playedDecompress them before they are played

Streaming – alternative to downloadingStreaming – alternative to downloading Sound is transmitted to user continuously instead of Sound is transmitted to user continuously instead of

in a single filein a single file Requires special server and user plug-inRequires special server and user plug-in

SoundSound

Streaming choices:Streaming choices: RealAudioRealAudio QuickTimeQuickTime Windows MediaWindows Media

ProblemProblem Sound quality generally not as good as a CDSound quality generally not as good as a CD

RealPlayer StreamingRealPlayer Streaming

Browser link to RealPlayer fileBrowser link to RealPlayer file Does Does notnot go to the actual file go to the actual file Links to a RealPlayer Links to a RealPlayer metafilemetafile on a special on a special

serverserver Sent back to your PCSent back to your PC

Metafile containsMetafile contains Links to the actual sound file location (URL)Links to the actual sound file location (URL) Instructions to browser on how to play the fileInstructions to browser on how to play the file

RealPlayer StreamingRealPlayer Streaming

Metafile launches the RealPlayer softwareMetafile launches the RealPlayer software RealPlayerRealPlayer

Contacts the URL found in the metafileContacts the URL found in the metafile URL points to a RealPlayer serverURL points to a RealPlayer server

Not a regular Web serverNot a regular Web server Specifically designed to deliver RealPlayer dataSpecifically designed to deliver RealPlayer data

RealPlayer StreamingRealPlayer Streaming

RealPlayer software and serverRealPlayer software and server Communicate with each otherCommunicate with each other

User’s Internet connection speedUser’s Internet connection speed

If slowIf slow A small, lower quality file sent to userA small, lower quality file sent to user

If highIf high Larger, higher quality file sentLarger, higher quality file sent

RealPlayer StreamingRealPlayer Streaming

Sound files are generally too large to be Sound files are generally too large to be sent as issent as is

Instead, they are compressedInstead, they are compressed IP packet sent using UDPIP packet sent using UDP

User Datagram ProtocolUser Datagram Protocol

UDP does UDP does notnot replace packets lost in replace packets lost in transmissiontransmission Sound player at user end would have to wait for Sound player at user end would have to wait for

the missing packet thus interrupting the audiothe missing packet thus interrupting the audio

RealPlayer StreamingRealPlayer Streaming

Packets arrive at user and are stored in a Packets arrive at user and are stored in a bufferbuffer

When buffer is full the packets are sent to When buffer is full the packets are sent to the RealPlayer playerthe RealPlayer player

While data from the buffer is being played, While data from the buffer is being played, more data is being loaded from the more data is being loaded from the RealPlayer serverRealPlayer server

RealPlayer StreamingRealPlayer Streaming

User can jump ahead (or back) in the fileUser can jump ahead (or back) in the file RealPlayer may pause while re-loading RealPlayer may pause while re-loading

the bufferthe buffer Contacting RealPlayer site to get fresh set of Contacting RealPlayer site to get fresh set of

packetspackets

MP3MP3

Uses special compression algorithmUses special compression algorithm Shrinks file sizeShrinks file size Retains CD-like music qualityRetains CD-like music quality

Process begins by recording the musicProcess begins by recording the music Same as normal recordingSame as normal recording

Special MP3 software (Special MP3 software (ripperripper)) Converts to MP3 formatConverts to MP3 format File size typically <= 3MBFile size typically <= 3MB

MP3MP3

MP3 file posted on InternetMP3 file posted on Internet You visit the MP3 site and download the You visit the MP3 site and download the

filefile Played using a special playerPlayed using a special player

Portable (iPOD)Portable (iPOD) On regular PCOn regular PC

Can also be streamedCan also be streamed

MP3MP3

Major problem with copyright infringementMajor problem with copyright infringement Many MP3 files created without original artists Many MP3 files created without original artists

permissionpermission

Can be downloaded to an MP3 playerCan be downloaded to an MP3 player Internal memoryInternal memory Memory cardMemory card Erased and replacedErased and replaced iPod records to end of storage before reusing iPod records to end of storage before reusing

deleted space at beginningdeleted space at beginning

Internet Broadcast RadioInternet Broadcast Radio

Two main typesTwo main types Traditional radio stations that have an Internet Traditional radio stations that have an Internet

componentcomponent Internet-only stationsInternet-only stations

Content still virtually the sameContent still virtually the same MusicMusic NewsNews TalkTalk

Internet Broadcast RadioInternet Broadcast Radio

For InternetFor Internet Station’s content converted to a digital formatStation’s content converted to a digital format

RealPlayer (RealPlayer (www.realplayer.com) ) Windows Media Player (Windows Media Player (www.microsoft.com) )

Stored on a Web serverStored on a Web server www.musicmatch.com

To listen,To listen, Launch playerLaunch player Select station from online listSelect station from online list

Internet Broadcast RadioInternet Broadcast Radio

Player software contacts serverPlayer software contacts server Server sends data in a streamServer sends data in a stream Software plays streamed data as it is Software plays streamed data as it is

receivedreceived User controls like a radioUser controls like a radio High-speed connection usually means High-speed connection usually means

better qualitybetter quality