Media Access Events

This specification defined a set of DOM 3 Events [DOM3EV] compatible events and DOM APIs related to media access. The defined events and APIs enables detailed monitoring of media stream buffering and initialization. They were designed to be easily combined with the SVG Tiny 1.2 [SVGT12] uDOM but could equally well be combined with other, larger DOM APIs.

Status of this Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.

This is a Working Group Note of "Media Access Events".

This specification was released in 2006 for public feedback regarding the overall design and functionality; in particular, whether it meet the needs of OMA, ISO SC 29, SVG, and SMIL for event-driven access to streaming media. This Note is being published as work on this specification has been stopped due to lack of implementer interest. It should not be implemented.

This document was developed by the SVG Working Group.

Please send comments to www-svg@w3.org, the public email list for issues related to SVG. Archives of the list are available.

Publication as a Working Group Note does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the W3C Patent Policy.

This document is governed by the 1 February 2018 W3C Process Document.

1. Introduction

This section is informative.

Streamable media, such as audio and video, is streamed over the network and is processed on the client as it arrives. This leads to different behaviour compared to downloaded media. The client normally holds a buffer where it stores part of the media prior to processing it. The state of this buffer affects the client. For example, if the buffer fills too slowly in relation to client processing the client will have to stall processing while it waits for the buffer to fill. It is often of interest to monitor the state of the buffer and client, and the purpose of correlating media access events introduced in this specification is to facilitate such monitoring. Initialising a session containing one or several media streams often takes a considerable amount of time. The author may wish to give the user some feedback that this setup is in progress and, when setup is done, present information of the available media streams.

2. Definitions

The Media Access Events namespace is http://www.w3.org/ns/media-access-event# .

The examples in this specification use a namespace prefix of me to denote the Media Access Events namespace .

A session is a set of synchronized streams rendered by a single media element.

3. State chart

This section is informative.

The following state chart illustrates the flow of events generated when streaming a media resource. Even if multiple streams are rendered by a single media element within one session , only one event is fired at each stage.

This chart can be explained as follows:

• The UA goes into the Setting Session state, firing a 'BeginSessionSetup' event. If a connection request needs to be sent to the server, it is sent during this phase.
• The UA goes into the Session Setup state, firing a 'EndSessionSetup' event, upon completion of the session set up on the terminal. If the session setup cannot be completed, the UA goes into the Stopped state and fires a 'Error' event. If a connection to a server was attempted, it was successful.
• The UA goes into the Reception state, firing a 'DataRequest' event, while sending a request for data to the server. If the data request cannot be sent, the UA goes into the Stopped state and fires a 'Error' event. While in this state, the UA may fire 'DataReceptionProgress' events.
• The UA goes into the Reception and Playing state, firing a 'Playable' event, when enough data has been received to start playing. If the operation is unsuccessful, the UA goes into the Stopped state and fires a 'Error' event. While in this state, the UA may fire 'DataReceptionProgress' events.
• From the Reception and Playing state, the UA may either go into the Playing state, firing a 'EndOfDataReception' event, when the end of the data has arrived, or back into the Reception state, firing a 'NotPlayable' event if there is not enough data available to continue playing. If the operation is unsuccessful, the UA goes into the Stopped state and fires a 'Error' event.
• From the Playing state, the UA goes into the Stopped state, firing a 'Stop' event, at the end of the playing of available data. If the operation is unsuccessful, the UA goes into the Stopped state and fires a 'Error' event.

4. The MediaAccessEvent interface

The Media Access Event module contains basic event types associated with media access. This interface inherits from the Event interface in the SVG uDOM [SVGT12].

interface MediaAccessEvent : events::Event {

  // MediaAccessEvent
  const unsigned short      STATUS_OK                           = 0;
  const unsigned short      STATUS_ERROR_ON_SETUP               = 1;
  const unsigned short      STATUS_ERROR_UNSUPPORTED_MEDIA      = 2;
  const unsigned short      STATUS_ERROR_CORRUPT_STREAM         = 3;

  readonly attribute boolean         bufferLevelValid;
  readonly attribute unsigned long   bufferLevel;
  readonly attribute float           bufferRemainingTime;
  readonly attribute unsigned short  status;
  DOMString           getSessionName();
  MediaStreamInfoList getMediaStreams();
};

The Media Access event types are listed below.

Even if a state is not relevant to a particular delivery protocol or implementation, the corresponding events MUST be fired. For example, if there is no session setup phase, then events 'BeginSessionSetup' , 'EndSessionSetup' and 'DataRequest' MUST be fired together in that order.

There MUST be at most one event of each of the following types sent within one session : 'BeginSessionSetup' , 'EndSessionSetup' , 'DataRequest' , 'EndOfDataReception' , 'Stop' , 'Error'

There MAY be more than one event of each of the following types sent within one session : 'DataReceptionProgress' , 'Playable' , 'NotPlayable'

5. The MediaStreamInfo interface

The MediaStreamInfo interface stores information about a media stream.

interface MediaStreamInfo {
  readonly attribute DOMString  mediaType;
  readonly attribute DOMString  transport;
  readonly attribute DOMString  format;
};

6. The MediaStreamInfoList interface

Returns the index th item in the collection. If index is greater than or equal to the number of MediaStreamInfo s in the list, this returns null .

interface MediaStreamInfoList {
  readonly attribute unsigned long  length;
  MediaStreamInfo    item(in unsigned long index);
};

7. Conformance

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

Unless otherwise specified immediately following the header, all sections in this document - to the exclusion of examples which are all informative - are normative.

8. Examples of usage

This section is informative.

Three examples to illustrate the usage of streaming events.

<svg xmlns="http://www.w3.org/2000/svg" version="1.2" baseProfile="tiny"
xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ev="http://www.w3.org/2001/xml-events"
xmlns:se="http://www.w3.org/ns/media-access-event#" width="100%" height="100%"
viewBox="0 0 400 300">
    <video id="exampleMovie" type="video/h264" xlink:href="rtsp://example.org/movies/exampleMovie.sdp"
           x="0" y="0" width="400" height="300"/>
    <text display="none" id="information" fill="white" x="50" y="50" font-size="30">
         <set attributeName="display" to="inline" begin="exampleMovie.NotPlayable" fill="freeze"/>
         <set attributeName="display" to="none" begin="exampleMovie.Playable" fill="freeze"/>
        Buffering
    </text>
</svg>

<svg xmlns="http://www.w3.org/2000/svg" version="1.2" baseProfile="tiny"
xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ev="http://www.w3.org/2001/xml-events"
xmlns:se="http://www.w3.org/ns/media-access-event#">
    <script type="application/ecmascript"><![CDATA[
        function initSetup (evt) {
            var setupAnimation = document.getElementById('setupAnimation');
            setupAnimation.setAttributeNS("http://www.w3.org/2000/svg", "visibility", "visible");
            setupAnimation.beginElement();
        }

        function exitSetup (evt) {
            var setupAnimation = document.getElementById('setupAnimation');
            setupAnimation.setAttributeNS("http://www.w3.org/2000/svg", "visibility", "hidden");
            setupAnimation.endElement();
        }

        function bufferStart (evt) {
            var progressBar = document.getElementById('progressBar');
            progressBar.setAttributeNS("http://www.w3.org/2000/svg", "width", "0");
            progressBar.setAttributeNS("http://www.w3.org/2000/svg", "visibility", "visible");
            var bufferAnimation = document.getElementById('bufferAnimation');
            bufferAnimation.setAttributeNS("http://www.w3.org/2000/svg", "visibility", "visible");
            bufferAnimation.beginElement();
        }

        function bufferProgress (evt) {
            var progressBar = document.getElementById('progressBar');
            progressBar.setAttributeNS("http://www.w3.org/2000/svg", "width", 100*(evt.bufferFillLevel));
        }

        function bufferComplete (evt) {
            var progressBar = document.getElementById('progressBar');
            progressBar.setAttributeNS("http://www.w3.org/2000/svg", "visibility", "hidden");
            var bufferAnimation = document.getElementById('bufferAnimation');
            bufferAnimation.setAttributeNS("http://www.w3.org/2000/svg", "visibility", "hidden");
            bufferAnimation.endElement();
        }
    ]]></script>

    <video id="exampleMovie" type="video/h264" xlink:href="rtsp://example.org/movies/exampleMovie.sdp"
           x="0" y="0" width="400" height="300">
        <handler type="application/ecmascript" ev:event="me:BeginSessionSetup">
            initSetup(evt);
        </handler>

        <handler type="application/ecmascript" ev:event="me:EndSessionSetup">
            exitSetup(evt);
        </handler>

        <handler type="application/ecmascript" ev:event="me:NotPlayable">
            bufferStart(evt);
        </handler>

        <handler type="application/ecmascript" ev:event="me:DataRequest">
            bufferStart(evt);
        </handler>

        <handler type="application/ecmascript" ev:event="me:DataReceptionProgress">
            bufferProgress(evt);
        </handler>

        <handler type="application/ecmascript" ev:event="me:Playable">
            bufferComplete(evt);
        </handler>
    </video>

    <g> ...
        <animate id="bufferAnimation" ... />
    </g>

    <g> ...
        <animate id="setupAnimation" ... />
    </g>

    <rect id="progressBar" ... />
</svg>

8.3. Stream info box

This example shows streaming of video within svg. An svg-button is available and when clicked it displays a box with information about the video stream. As with the example above this one isn't runnable as is since the svg markup isn't complete. The image to the right shows a possible rendering of the info box in this example.

Example: Using MediaAccessEvents in SVG to display a stream info box

<svg xmlns="http://www.w3.org/2000/svg" version="1.2" baseProfile="tiny"
xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ev="http://www.w3.org/2001/xml-events"
xmlns:se="http://www.w3.org/ns/media-access-event#">
    <script type="application/ecmascript"><![CDATA[
        function sessionSetupComplete (evt) {
            var sessionName, sessionProtocol;
            var streamFormat, mediaType;
            sessionName = evt.sessionName;
            if (sessionName == 0) sessionName = "No session name available";
            var streamList = evt.getMediaStreams();
            var stream = streamList.item(0);
            if (stream == 0){
                sessionProtocol = "N/A";
                streamFormat = "N/A";
                mediaType = "N/A";
            }
            else{
                sessionProtocol = stream.transport;
                streamFormat = stream.format;
                mediaType = stream.mediaType;
            }
            document.getElementById('sessionNameText').textContent = "Session name: " + sessionName;
            document.getElementById('sessionProtocolText').textContent = "Streaming protocol: " + sessionProtocol;
            document.getElementById('sessionTypeText').textContent = "Streaming media: " + mediaType;
            document.getElementById('sessionFormatText').textContent = "Format/codec: " + streamFormat;
        }

        function showInfo (evt) {
            var infoBox = document.getElementById('infoBox');
            setupAnimation.setAttributeNS("http://www.w3.org/2000/svg", "visibility", "visible");
        }

        function hideInfo (evt) {
            var infoBox = document.getElementById('infoBox');
            setupAnimation.setAttributeNS("http://www.w3.org/2000/svg", "visibility", "hidden");
        }
    ]]></script>

    <video id="exampleMovie" type="video/h264" xlink:href="rtsp://example.org/movies/exampleMovie.sdp"
           x="0" y="0" width="400" height="300">
        <handler type="application/ecmascript" ev:event="me:EndSessionSetup">
            sessionSetupComplete(evt);
        </handler>
    </video>

    <g id="infoButton"> ...
        <handler type="application/ecmascript" ev:event="ev:DOMActivate">
            showInfo(evt);
        </handler>
    </g>

    <g id="infoBox"> ...
        <text id="sessionNameText" ...></text>
        <text id="sessionProtocolText" ...></text>
        <text id="sessionTypeText" ...></text>
        <text id="sessionFormatText" ...></text>

        <g id="okButton"> ...
            <handler type="application/ecmascript" ev:event="ev:DOMActivate">
                hideInfo(evt);
            </handler>
        </g>
    </g>
</svg>

9. Acknowledgements

This section is informative.

The authors would like to thank Cyril Concolato for his thorough review and excellent contribution. We would also like to thank Robin Berjon for ReSpec, the editorial framework upon which this specification is written.

A. References

DOM3EV

Document Object Model (DOM) Level 3 Events Specification, Philippe Le Hégaret (W3C), and Tom Pixley (Netscape Communications Corporation).

MIME-Media-Types

IANA MIME Media Types,

RFC2119

Key words for use in RFCs to Indicate Requirement Levels, S. Bradner.

SVGT12

Scalable Vector Graphics (SVG) Tiny 1.2 Specification, Ola Andersson <ola.andersson@ikivo.com>, Robin Berjon <robin.berjon@expway.fr>, Jon Ferraiolo <jon.ferraiolo@adobe.com>, Vincent Hardy <vincent.hardy@sun.com>, Scott Hayman, Dean Jackson <dean@w3.org>, Craig Northway <craign@cisra.canon.com.au>, and Antoine Quint <aq@fuchsia-design.com>.