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+
+Audio and Apache HTTPD
+ApacheCon 2001
+Santa Clara, US
+
+April 6th, 2001
+
+Sander van Zoest <sander@vanZoest.com>
+Covalent Technologies, Inc. 
+<http://www.covalent.net/>
+
+Latest version can be found at:
+ <http://www.vanZoest.com/sander/apachecon/2001/>
+
+Introduction:
+
+About this paper:
+
+Contents:
+
+ 1. Why serve Audio on the Net?
+
+ This is almost like asking, why are you reading this? it might be
+ because of the excitement caused by the new media that has recently
+ crazed upon the internet. People are looking to bring their lifes onto
+ the net, one of the things that brings that closer to a reality is the
+ ability to hear live broadcasts of the worlds news, favorite sport; 
+ hear music and to teleconference with others. Sometimes it is simply
+ to enhance the mood to a web site or to provide audio feedback of
+ actions performed by the visitor of the web site.
+
+ 2. What makes delivering audio so different?
+
+ The biggest reason to what makes audio different then traditional
+ web media such as graphics, text and HTML is the fact that timing
+ is very important. This caused by the significant increase in size
+ of the media and the different quality levels that exist.
+
+ There really are two kinds of goals behind audio streams.
+ In one case there is a need for immediate response the moment
+ playback is requested and this can sacrifice quality. While
+ in the other case quality and a non-interrupted stream are much
+ more important.
+
+ This sort of timing is not really required of any other media,
+ with the exception of video. In the case of HTML and images the
+ files sizes are usually a lot smaller which causes the objects
+ to load much quicker and usually are not very useful without
+ having the entire file. In audio the middle of a stream can have
+ useful information and still set a particular mood.
+ 
+ 3. Different ways of delivery Audio on the Net.
+ Embedding audio in your Web Page
+
+ This used to be a lot more common in the past. Just like embedding
+ an image in a web page, it is possible to add a sound clip or score
+ to the web page.
+
+ The linked in audio files are usually short and of low quality to 
+ avoid a long delay for downloading the rest of the web page and the
+ audio format needs to be supported by the browser natively or with
+ a browser plug-in to avoid annoying the visitor.
+
+ This can be accomplished using the HTML 4.0 [HTML4] object element which
+ works similar to how to specify an applet with the object element.
+ In the past this could also be accomplished using the embed and bgsound
+ browser specific additions to HTML.
+
+ example:
+   <object type="audio/x-midi" data="../media/sound.mid" width="200" height="26">
+     <param name="src" value="../media/sound.mid">
+     <param name="autostart" value="true">
+     <param name="controls" value="ControlPanel">
+   </object> 
+
+ Each param element is specific to each browser. Please check with each
+ browser for specific information in regards to what param elements are
+ available.
+
+ In this method of delivering audio the audio file is served up via the
+ web server. When using an Apache HTTPD server make sure that the appropriate
+ mime type is configured for the audio file and that the audio file is
+ named and referenced by the appropriate extension.
+
+ Although the current HTML 4.01 [HTML4] says to use the object element
+ many browsers out on the market today still look for the embed element.
+ Below find a little snipbit that will work work in many browsers.
+
+  <object type="audio/x-midi" data="../media/sound.mid" width="200" height="26">
+    <param name="src" value="../media/sound.mid">
+    <param name="autostart" value="true">
+    <param name="controls" value="ControlPanel">
+
+    <embed type="audio/x-midi" src="../media/sound.mid"
+     width="200" height="26" autoplay="true" controls="ControlPanel">
+    <noembed>Your browser does not support embedded WAV files.</noembed>
+  </object> 
+
+ With the increasing installation base of the Flash browser plug-in by
+ Macromedia most developers that are looking to provide this kind of
+ functionality to a web page are creating flash elements that have their
+ own way of adding audio that is discussed in Flash specific documents.
+
+ Downloading via HTTP
+
+ Using this method the visitor to the website will have to download the
+ entire audio file and save it to the hard drive before it can be
+ listened to. (1) This is very popular with people that want to listen 
+ to high quality streams of audio and have a below ISDN connection to
+ the internet. In some cases where the demand for a stream is high or
+ the internet is congested downloading the content even for high bandwidth
+ users can be affective and useful.
+
+ One of the advantages of downloading audio to the local computer hard
+ drive is that it can be played back (once downloaded) any time as long
+ as the audio file is accessable from the computer.
+
+ There are a lot of sites on the internet that provide this functionality
+ for music and other audio files. It is also one of the easiest ways to
+ delivery high quality audio to visitors.
+ 
+ (1) Microsoft Windows Media Player in conjunction with the Microsoft
+     Internet Explorer Browser will automaticly start playing the 
+     audio stream after a sufficient amount of the file has been 
+     downloaded. This can be accomplished because of the tight 
+     integration of the Browser and Media Player. With most audio players
+     you can listen to a file being downloaded, but you will have to
+     envoke the action manually.
+ 
+ . On-Demand streaming via HTTP
+
+ The real difference between downloading and on-demand streaming is
+ that in on-demand streaming the audio starts playing before the entire
+ audio file has been downloaded. This is accomplished by a hand of off
+ the browser to the audio player via an intermediate file format that
+ has been configured by the browser to be handled by the audio player.
+
+ Look in a further section entitled "Linking to Audio via Apache HTTPD"
+ below for more information about the different intermediate file formats.
+
+ This type of streaming is very popular among the open source crowd and
+ is the most widely implemented using the MP3 file format. Apache,
+ Shoutcast [SHOUTCAST] and Icecast [ICECAST] are the most common 
+ software components used to provide on-demand streaming via HTTP. Both
+ Icecast and Shoutcast are not fully HTTP compliant, but Icecast is 
+ becoming closer. For more information about the Shoutcast and Icecast 
+ differences see the section below.
+
+ Sites like Live365.com and MP3.com are huge sites that rely on this
+ method of delivery of audio.
+
+ . On-Demand Streaming via RTSP/RTP
+
+ RTSP/RTP is a new set of streaming protocols that is getting more 
+ backing and becoming more popular by the second. The specification
+ was developed by the Internet Engineering Task Force Working Groups
+ AVT [IETFAVT] and MMUSIC [IETFMMUSIC]. RTP the Realtime Transfer
+ Protocol has been around longer then RTSP and originally came out
+ of the work towards a better teleconferencing, mbone, type system.
+ RTSP is the Real-Time Streaming Protocol that is used as a control
+ protocol and acts similarily to HTTP except that it maintains state
+ and is bi-directional.
+
+ Currently the latest Real Networks Streaming Servers support RTSP
+ and RTP and Real Networks own proprietary transfer protocol RDT.
+ Apple's Darwin Streaming server is also RTSP/RTP compliant.
+
+ The RTSP/RTP protocol suite is very powerful and flexable in regards
+ to your streaming needs. It has the ability to suport "server-push"
+ style stream redirects and has the ability to throttle streams to
+ ensure the stream can sustain the limited bandwidth over the network.
+
+  For On-Demand streams the RTP protocol would usually stream over
+ TCP and have a second TCP connection open for RTSP. Because of the
+ rich features provided by the protocol suite, it is not very well
+ suited to allow people to download the stream and therefore the
+ download via HTTP method might still be preferred by some.
+
+ . Live Broadcast Streaming via RTSP/RTP
+
+ In the case of a live broadcast streaming RTSP/RTP shines. RTP allowing
+ for UDP datagrams to be transmitted to clients allows for fast immediate
+ delivery of content with the sacrifice of reliability. The RTP stream
+ can be send over IP Multicast to minimize bandwidth on the network.
+
+ Many Content Delivery Networks (CDNs) are starting to provide support for
+ RTSP/RTP proxies that should provide a better quality streaming environment
+ on the internet. 
+
+ Much work is also being done in the RTP space to provide transfers over 
+ telecommunication networks such as cellular phones. Although not directly
+ related, per se, it does provide a positive feeling knowing that all the
+ audio related transfer groups seem to be working towards a common standard
+ such as RTP.
+
+ . On-Demand or Live Broadcast streaming via MMS.
+
+ This is the Microsoft Windows Media Technologies Streaming protocol. It
+ is only supported by Microsoft Windows Media Player and currently only
+ works on Microsoft Windows.
+
+ 5. Configuring Mime Types
+
+ One of the most hardest things in serving audio has been the wide variety
+ of audio codecs and mime types available. The battle of mime types on the
+ audio player side of things isn't over, but it seems to be a little more
+ controlled.
+
+ On the server side of things provide the appropriate mime type for the 
+ particular audio streams and/or files that are being served to the audio 
+ players. Although some clients and operating systems handle files fully 
+ based on the file extension. The mime type [RFC2045] is more specific 
+ and more defined.
+
+ The registered mime types are maintained by IANA [IANA]. On their site
+ they have a list of all the registered mime types and their name space.
+
+ If you are planning on using a mime type that isn't registered by IANA
+ then signal this in the name space by adding a "x-" before the subtype. 
+ Because this was not done very often in the audio space, there was a 
+ lot of confusion to what the real mime type should be.
+
+ For example the MPEG 1.0 Layer 3 Audio (MP3) [ORAMP3BOOK] mime type 
+ was not specified for the longest time. Because of this the mime type 
+ was audio/x-mpeg. Although none of the audio players understood 
+ audio/x-mpeg, but understood audio/mpeg it was not a technically 
+ correct mime type. Later audio players recognized this and started 
+ using the audio/x-mpeg mime type. Which in the end caused a lot 
+ of hassles with clients needing to be configured differently depending
+ on the website and client that was used. Last november we thanked
+ Martin Nilsson of the ID3 tagging project for registering audo/mpeg
+ with IANA. [RFC3003]
+
+ Correct configuration of Mime Types is very important. Apache HTTPD
+ ships with a fairly up to date copy of the mime.types file, so most
+ of the default ones (including audio/mpeg) are there.
+
+ But in case you run into some that are not defined use the mod_mime 
+ directives such as AddType to fix this.
+
+ Examples:
+	AddType audio/x-mpegurl .m3u
+        AddType audio/x-scpls   .pls
+        AddType application/x-ogg .ogg
+
+
+ 6. Common Audio File Formats
+
+ There are many audio formats and metadata formats that exist. Many of
+ them do not have registered mime types and are hardly documented.
+ This section is an attempt at providing the most accurate mime type
+ information for each format with a rough description of what the files
+ are used for.
+
+ . Real Audio
+ 
+   Real Networks Proprietary audio format and meta formats. This is one
+   of the more common streaming audio formats today. It comes in several
+   sub flavors such as Real 5.0, Real G2 and Real 8.0 etc. The file size
+   varies depending on the bitrates and what combination of bitrates are
+   contained within the single file.
+   The following mime types are used
+      audio/x-pn-realaudio .ra, .ram, .rm
+      audio/x-pn-realaudio-plugin .rpm
+      application/x-pn-realmedia
+
+ . MPEG 1.0 Layer 3 Audio (MP3)
+   
+   This is currently one of the most popular downloaded audio formats
+   that was originally developed by the Motion Pictures Experts Group
+   and has patents by the Fraunhofer IIS Institute and Thompson 
+   Multimedia. [ORAMP3BOOK] The file is a lossy compression that at
+   a bitrate of 128kbps reduces the file size to roughly a MB/minute.
+   The mime type is audio/mpeg with the extension of .mp3 [RFC3003]
+
+ . Windows Media Audio
+   
+   Originally known as MS Audio was developed by Microsoft as the MP3
+   killer. Still relatively a new format but heavily marketed by
+   Microsoft and becoming more popular by the minute. It is a successor
+   to the Microsoft Audio Streaming Format (ASF).
+
+ . WAV
+
+   Windows Audio Format is a pretty semi-complicated encapsulating 
+   format that in the most common case is PCM with a WAV header up front.
+   It has the mime type audio/x-wav with the extension .wav.
+
+ . Vorbis
+
+   Ogg Vorbis [VORBIS] is still a relatively new format brought to 
+   life by CD Paranoia author Christopher Montgomery; known to the 
+   world as Monty. It is an open source audio format free of patents 
+   and gotchas. It is a codec/file format that is roughly as good as
+   the MP3 format, if not much better. The mime type for Ogg Vorbis is
+   application/x-ogg with the extension of .ogg.
+
+ . MIDI
+
+   The MIDI standard and file format [MIDISPEC] have been used by 
+   Musicians for a long time. It is a great format to add music to
+   a website without the long download times and needing special players
+   or plug-ins. The mime type is audio/x-midi and the extension is .mid
+
+ . Shockwave Flash (ADPCM/MP3) [FLASH4AUDIO]
+
+   Macromedia Flash [FLASH4AUDIO] uses its own internal audio format
+   that is often used on Flash websites. It is based on Adaptive 
+   Differential Pulse Code Modulation (ADPCM) and the MP3 file format.
+   Because it is usually used from within Flash it usually isn't served
+   up seperatedly but it's extension is .swf
+
+ There are many many many more audio codecs and file formats that exist.
+ I have listed a few that won't be discussed but should be kept in mind.
+ Formats such as PCM/Raw Audio (audio/basic), MOD, MIDI (audio/x-midi),
+ QDesign (used by Quicktime), Beatnik, Sun's AU, Apple/SGI's AIFF, AAC
+ by the MPEG Group, Liquid Audio and AT&T's a2b (AAC derivatives),
+ Dolby AC-3, Yamaha's TwinVQ (originally by Nippon Telephone and Telegraph)
+ and MPEG-4 audio.
+
+ 7. Linking to Audio via Apache HTTPD
+
+ There are many different ways to link to audio from the Apache HTTPD
+ web server. It seems as if every codec has their own metafile format.
+ The metafile format is provided to allow the browser to hand off the
+ job of requesting the audio file to the audio player, because it is
+ more familiar with the file format and how to handle streaming or how
+ to actually connect to the audio server then the web browser is.
+
+ This section will discuss the more common methods to provide streaming
+ links to provide that gateway from the web to the audio world.
+
+ Probably the one that is the most recognized file is the RAM file.
+
+ . RAM
+
+ Real Audio Metafile. It is a pretty straight forward way that Real
+ Networks allowed their Real Player to take more control over their
+ proprietary audio streams. The file format is simply a URL on each
+ line that will be streamed in order by the client. The mime type
+ is the same as other RealAudio files audio/x-pn-realaudio where
+ the pn stands for Progressive Networks the old name of the company.
+
+ . M3U
+ 
+ This next one is the MPEG Layer 3 URL Metafile that has been around
+ for a very long time as a playlist format for MP3 players. It supported
+ URLs pretty early on by some players and got the mime type 
+ audio/x-mpegurl and is now used by Icecast and many destination sites
+ such as MP3.com. The format is exactly the same as that of the RAM
+ file, just a list of urls that are separated by line feeds.
+
+ . PLS
+ 
+ This is the playlist files used by Nullsoft's Winamp MP3 Player. Later
+ on it got more widely used by Nullsoft's Shoutcast and has the mime
+ type of audio/x-scpls with the extension .pls. Before shoutcast the
+ mimetype was simply audio/x-pls. As you can see in the example below
+ it looks very much like a standard windows INI file format.
+
+ Example:
+	[playlist]
+	numberofentries=2
+	File1=<uri>
+	Title1=<title>
+	Length1=<length or -1>
+	File2=<uri>
+	Title2=<title>
+	Length2=<length or -1>
+
+ . SDP 
+ 
+ This is the Session Description Protocol [RFC2327] which is heavily
+ used within RTSP and is a standard way of describing how to subscribe
+ to a particular RTP stream. The mime type is application/sdp with the
+ extension .sdp . 
+
+ Sometimes you might see RTSL (Real-Time Streaming Language) floating 
+ around. This was an old Real Networks format that has been succeeded 
+ by SDP. It's mimetype was application/x-rtsl with the extension of .rtsl
+ 
+ . ASX
+ 
+ Is a Windows Media Metafile format [MSASX] that is based on early XML
+ standards. It can be found with many extensions such as .wvx, .wax 
+ and .asx. I am not aware of a mime type for this format.
+ 
+ . SMIL
+
+ Is the Synchronized Multimedia Integration Language [SMIL20] that
+ is now a W3C Recommendation [W3SYMM]. It was originally developed
+ by Real Networks to provide an HTML-like language to their Real Player
+ that was more focused on multimedia. The mime type is application/smil
+ with the extensions of either .smil or .smi
+
+ . MHEG
+
+ Is a hypertext language developed by the ISO group. [MHEG1] [MHEG5] 
+ and [MHEG5COR]. It has been adopted by the Digital Audio Visual
+ Council [DAVIC]. It is more used for teleconferencing, broadcasting
+ and television, but close enough related that it receives a mention
+ here. The mime type is application/x-mheg with the extension of
+ .mheg
+
+ 8. Configuring Apache HTTPD specificly to serve large Audio Files
+
+ Some of the most common things that you will need to adjust to be
+ able to serve many large audio files via the Apache HTTPD Server.
+ Because of the difference in size between HTML files and Audio files,
+ the MaxClients will need to be adjusted appropriatedly depending on
+ the amount of time listeners end up tieing up a process. If you are
+ serving high quality MP3 files at 128kbps for example you should
+ expect more then 5 minute download times for most people.
+
+ This will significantly impact your webserver since this means that
+ that process is occupied for the entire time. Because of this you
+ will also want to in crease the TimeOut Directive to a higher 
+ number. This is to ensure that connections do not get disconnected
+ half way through a transfer and having that person hit "reload"
+ and connect again.
+
+ Because of the amount of time the downloads tie up the processes
+ of the server, the smallest footprint of the server in memory would
+ be recommended because that would mean you could run more processes
+ on the machine.
+
+ After that normal performance tweaks such as max file descriptor
+ changes and longer tcp listen queues apply.
+
+ 9. Icecast/Shoutcast Protocol.
+
+ Both protocols are very tightly based on HTTP/1.0. The main difference
+ is a group of new headers such as the icy headers by Shoutcast and the
+ new x-audiocast headers provided by Icecast.
+
+ A typical shoutcast request from the client.
+
+ GET / HTTP/1.0
+
+ ICY 200 OK
+ icy-notice1:<BR>This stream requires <a href="http://www.winamp.com/">
+             Winamp</a><BR>
+ icy-notice2:SHOUTcast Distributed Network Audio Server/posix v1.0b<BR>
+ icy-name: Great Songs
+ icy-genre: Jazz
+ icy-url: http://shout.serv.dom/
+ icy-pub: 1
+ icy-br: 24
+  
+ <data><songtitle><data>
+
+ The icy headers display the song title and other formation including if
+ this stream is public and what the bitrate is.
+
+ A typical icecast request from the client.
+
+ GET / HTTP/1.0
+ Host: icecast.serv.dom
+ x-audiocast-udpport: 6000
+ Icy-MetaData: 0
+ Accept: */*
+
+ HTTP/1.0 200 OK
+ Server: Icecast/VERSION
+ Content-Type: audio/mpeg
+ x-audiocast-name: Great Songs
+ x-audiocast-genre: Jazz
+ x-audiocast-url: http://icecast.serv.dom/
+ x-audiocast-streamid:
+ x-audiocast-public: 0
+ x-audiocast-bitrate: 24
+ x-audiocast-description: served by Icecast 
+
+ <data>
+
+ NOTE: I am mixing the headers of the controlling client with those form
+       a listening client. This might be better explained at a latter
+       date.
+ 
+ The CPAN Perl Package Apache::MP3 by Lincoln Stein implements a little of
+ each which works because MP3 players tend to support both.
+
+ One of the big differences in implementations between the listening clients 
+ is that Icecast uses an out of band UDP channel to update metadata
+ while the Shoutcast server gets it meta data from the client embedded within
+ the MP3 stream. The general meta data for the stream is set up via the
+ icy and x-audiocast HTTP headers.
+
+ Although the MP3 standard documents were written for interrupted communication
+ it is not very specific on that. So although it doesn't state that there is
+ anything wrong with embedding garbage between MPEG frames the players that
+ do not understand it might make a noisy bleep and chirps because of it.
+
+References and Further Reading:
+
+[DAVIC]
+       Digital Audio Visual Council 
+       <http://www.davic.org/>
+
+[FLASH4AUDIO]
+       L. J. Lotus, "Flash 4: Audio Options", ZD, Inc. 2000.
+       <http://www.zdnet.com/devhead/stories/articles/0,4413,2580376,00.html>
+
+[HTML4]
+       D. Ragget, A. Le Hors, I. Jacobs, "HTML 4.01 Specification", W3C
+       Recommendation, December, 1999.
+       <http://www.w3.org/TR/html401/>
+
+[IANA]
+        Internet Assigned Numbers Authority.
+        <http:/www.iana.org/>
+
+[ICECAST]
+        Icecast Open Source Streaming Audio System.
+        <http://www.icecast.org/>
+
+[IETFAVT]
+        Audio/Video Transport WG, Internet Engineering Task Force.
+        <http://www.ietf.org/html.charters/avt-charter.html>
+
+[IETFMMUSIC]
+       Multiparty Multimedia Session Control WG, Internet Engineering Task
+       Force. <http://www.ietf.org/html.charters/mmusic-charter.html>
+
+[IETFSIP]
+       Session Initiation Protocol WG, Internet Engineering Task Force.
+       <http://www.ietf.org/html.charters/sip-charter.html>
+
+[IPMULTICAST]
+       Transmit information to a group of recipients via a single transmission
+       by the source, in contrast to unicast.
+       IP Multicast Initiative
+       <http://www.ipmulticast.com/>
+
+[MIDISPEC]
+       The International MIDI Association,"MIDI File Format Spec 1.1",
+       <http://www.vanZoest.com/sander/apachecon/2001/midispec.html>
+
+[MHEG1]
+       ISO/IEC, "Information Technology - Coding of Multimedia and Hypermedia
+       Information - Part 1: MHEG Object Representation, Base Notation (ASN.1)"; 
+       Draft International Standard ISO 13522-1;1997;
+       <http://www.ansi.org/>
+       <http://www.iso.ch/cate/d22153.html>
+
+[MHEG5]
+       ISO/IEC, "Information Technology - Coding of Multimedia and Hypermedia
+       Information  - Part 5: Support for Base-Level Interactive Applications";
+       Draft International Standard ISO 13522-5:1997;
+       <http://www.ansi.org/>
+       <http://www.iso.ch/cate/d26876.html>
+
+[MHEG5COR]
+       Information Technology - Coding of Multimedia and Hypermedia Information
+       - Part 5: Support for base-level interactive applications -
+       - Technical Corrigendum 1; ISO/IEC 13552-5:1997/Cor.1:1999(E)
+       <http://www.ansi.org/>
+       <http://www.iso.ch/cate/d31582.html>
+
+[MSASX]
+        Microsoft Corp. "All About Windows Media Metafiles". October 2000.
+        <http://msdn.microsoft.com/workshop/imedia/windowsmedia/
+         crcontent/asx.asp>
+
+[ORAMP3]
+	S. Hacker; MP3: The Definitive Guide; O'Reilly and Associates, Inc.
+        March, 2000.
+        <http://www.oreilly.com/catalog/mp3/>
+[RFC2045]
+        N. Freed and N. Borenstein, "Multipurpose Internet Mail 
+        Extensions (MIME) Part One: Format of Internet Message Bodies",
+        RFC 2045, November 1996. <http://www.ietf.org/rfc/2045.txt>
+
+[RFC2327]
+	M. Handley and V. Jacobson, "SDP: Session Description Protocol",
+        RFC 2327, April 1998. <http://www.ietf.org/rfc/rfc2327.txt>
+
+[RFC3003] 
+        M. Nilsson, "The audio/mpeg Media Type", RFC 3003, November 2000.
+        <http://www.ietf.org/rfc/rfc3003.txt>
+
+[SHOUTCAST]
+	Nullsoft Shoutcast MP3 Streaming Technology.
+        <http://www.shoutcast.com/>
+
+[SMIL20]
+        L. Rutledge, J. van Ossenbruggen, L. Hardman, D. Bulterman,
+        "Anticipating SMIL 2.0: The Developing Cooperative Infrastructure 
+        for Multimedia on the Web"; 8th International WWW Conference, 
+        Proc. May, 1999.
+        <http://www8.org/w8-papers/3c-hypermedia-video/anticipating/
+         anticipating.html>
+
+[W39CIR]  
+        V. Krishnan and S. G. Chang, "Customized Internet Radio"; 9th
+        International WWW Conference Proc. May 2000.
+        <http://www9.org/w9cdrom/353/353.html>
+
+[VORBIS]
+	Ogg Vorbis - Open Source Audio Codec
+        <http://www.xiph.org/ogg/vorbis/>
+
+[W3SYMM] 
+        W3C Synchronized Multimedia Activity (SYMM Working Group);
+        <http://www.w3.org/AudioVideo/>