Timing and Synchronisation

7 Timing and Synchronisation At the Heart of SMIL

7.1 Role of Timing

Controlled using a standard set of attributes

Use of timing attributes is optional

Time behaviour inherent in groups provides basic timing behaviour

begin=“0”

May be sufficient for a simple SMIL presentation

SMIL is not really about time but structure!

Timing attributes used with group, media and other elements

<par> <seq> <audio> <set> <animate>

Provides very fine temporal control

Timing can be down to 1/1000 th of a second

begin=“15.75”

Timing can be defined as an event

begin=“audio1.end”

Timing can be offset from + or - from and event or other timed element or group

begin=“audio1.end-2.5”

Wall clock timing is supported in the standard

Implemented in XHTML+TIME (IEv6) but not RealONE (in progress)

Tuning in to a webcast or beginning an event in another time zone

Examples

Real ONE

Internet Explorer v6

7.2 Expressing Timing Values

Differs slightly according to client

Each client supports various expressions

RealONE

begin=“30” begin=“30s” begin=“30.0s” begin=“0.5min”

QuickTime

begin=“30” begin=“30sec” begin=“30.000”

begin=“30”

Just use the ss.ms format

begin=“30” end=“30” dur=“15.75”

7.3 Defining Timing for Clips

Some types of clip have inherent timing

audio, video have their own durations

Timing can be used to address inherent timing

Play only part of an audio or video clip

Examples: RealONE , Internet Explorer v6

Timing is applied to a clip using one or more timing attributes

Attributes begin end and dur are the most frequently used

Timing can be defined relative to other clips

Begin playing audio 5 seconds before video ends

Timing behaviour of clips depends on their group context

Examples

Images in a <par> group

Timing is relative to the start of the group

RealONE

Images in a <seq> group

Timing is relative to the previous element in the group

RealONE

7.4 Element Timing Within Groups

Elements always located within a least one group

Group may be the implicit default behaviour

Elements time is relative to the containing group element

<seq>

Timing defined is relative the preceding element in the group

<par> and <excl>

Timing defined is relative to the beginning of the group

Default for top-level group element is begin=“0”

Examples

Timing within a <seq> group

RealONE

Quicktime (not handled correctly)

Timing within a <par> group

RealONE

QuickTime (make .mov)

Timing within an <excl> group

RealONE

7.5 Timing in Nested Element Groups

Element groups can be nested within each other

Element takes timing from the enclosing element group

par or excl element inside seq element

Timing of each par or excl element group is relative to the end of the previous par or excl element group in the sequence

seq element inside a par or excl group

Timing of each seq element group is relative to the start of the enclosing par or exclusive group

Timing of elements within any of the groups still observes the timing rules

Elements in a <par> group

Elements in a <seq> group

Timing is relative to the preceding element in the group

7.5.1 Example of Nested Timing

Examples

RealONE

Alternative solutions

7.6 Timing Attributes    Time & Synch repeatCount    Time & Synch repeatDur     Time & Synch fill     Time & Synch endsync    Media clipBegin clipEnd      Time & Synch begin end dur QT IEv6 RealONE SMIL2 SMIL1 Module Attribute

7.7 begin end and dur attributes

Remember timing depends upon the containing group element

begin controls when clips start to play

End always starts from “0”

Better used when defined with a clip event

Duration of clip is end minus begin

20 -10 = 10 seconds

Simpler to use dur attribute to set a clips duration

Do not use both end and dur

Attribute giving the shortest playback time is used

Use dur to override media clips inherent duration

Examples

RealONE

QuickTime

7.7.1 dur attribute continued

Using the media clip’s inherent duration

Supported in RealONE

Ignored for elements that do not define media

par , seq and excl elements

Using an indefinite duration

Can be used with media and group elements

Maintain an element until an event is caught

Use in SMIL file that is a wrapper for a live event

Examples

7.8 clipBegin and clipEnd

Define a part of a media clip with inherent timing

Audio, video or animation

clipBegin defines start point

clipEnd defines the

Will not work with

Live webcasts as the timing is unknown

Content delivered over HTTP

Can be combined with begin and end attributes

Start or end a clip on an event

End a clip extract before clipEnd value is reached

Examples

RealONE

<video src=“video_file” … clipBegin=“10” clipEnd=“25” …/>

7.9 Ending groups with endsync

Default is for groups to end when elements in group finish

Modify this behaviour with the endsync attribute

Possible uses

End group when specific media clip completes

End group when user has selected and played a specific clip

Ignored if the group has a dur or end attribute set

Examples

excl group with endsync=“all”

RealONE

par group with endsync=“id”

7.9.1 endsync attribute values IEv6 only. Ends when the group ends ignoring the enclosed clips (elements) This is the same as the behaviour in RealONE when a group has a dur or end attribute value set which overrides the endsync value. none Ends the group when the clip (element) with this id has finished. Note in EIv6 this does not appear to work with time based media id This is the default. Ends the group once the last clip (element) has finished last Ends the group when the first clip (element) has finished first Ends a group once all clips (elements) have finished all

7.10 Using the fill attribute

Used primarily with visual elements: images, video and text

Does not apply to audio clips

Define state when clip ends but its group is still active

Values

freeze hold remove transition

Default fillDefault can be defined for a group element

Not implemented in IE v6

Examples

RealONE

7.11 repeatCount and repeatDur

repeatCount defines the number of times an element repeats

Integer [2, 45], decimal [3.5, 5.0] and indefinite values

repeatDur sets the length of time and element repeats for

Using any valid time value

Also supports indefinite

Examples

Real ONE repeatCount repeatDur

Internet Explorer v6 repeatCount repeatDur

7.12 Advanced Timing

Let the client handle the time calculations 

Define in relation to an event

elementID.begin|end+|-{time}

Beginning or end of an element or event

Type of events supported depends upon the client

RealNetworks Production Guide

MSDN Reference Documentation

Element must have an id attribute set

Used to refer timing to that element

Negative offset cannot be used by elements in a seq group

Multiple begin and end values can be applied to elements

May need to prefetch streamed content that uses advanced timing

Examples

RealONE

7.12.1 Timing and Events

Handling events

Mouse click or mouse over

Depends on the events supported by the client

IE v6 has extensive events via DHTML

Requires scripting

RealONE player has far fewer events available

Examples

RealONE activateEvent accesskey combined

Internet Explorer v6 onclick combined events

7.13 Review

Timing is optional

Group elements and clips have inherent time properties

Timing is defined using element attributes

Syntax time values for attributes varies across clients

Simplest solution is to use plain seconds

RealONE, QT and IE all understand this format

Time behaviour depends on enclosing group

<par> and <excl> groups

<seq> group

Timing is relative to the preceding element

Timing of nested groups obeys these rules too!

Elements can be synchronised and repeated

Timing can be defined in relation to elements and events

Timing and Synchronisation

0 comments

Notes on slide 1

Favorites, Groups & Events