Parallel Clips

As you noticed in the last practice example, playback regions can define where media play, but not when. This is the default behavior for media when no timing tags are provided in the SMIL file. But what if you want to play more than one at a time? SMIL includes timing tags for this purpose.

The parallel tag indicates that one or more clips should be played at the same time (in parallel). It encloses the clips that form the "parallel" group. In the example below, all of the clips play/display simultaneously:

<par>

<audio src="rtsp://realserver.bu.edu:554/a/v/av/nis/training/smil/driving.rm"/>

<img region ="one" src="rtsp://realserver.bu.edu:554/a/v/av/nis/training/smil/one.gif"/>

<img region ="two" src="rtsp://realserver.bu.edu:554/a/v/av/nis/training/smil/two.gif"/>

<img region ="three" src="rtsp://realserver.bu.edu:554/a/v/av/nis/training/smil/three.gif"/>

</par>

You can end a group of clips at the same time by using the endsync attribute with the <par> tag.

Use the attribute endsync="first" to stop the <par> group when the clip with the shortest timeline finishes playing. All other clips in the group stop playing at that point, regardless of their playback status or any timing parameters specified for them.

The attribute endsync="last" causes the <par> group to conclude when all clips have finished playing. Because this is the default value, you can omit the endsync attribute from the <par> tag to achieve this effect.

The attribute endsync="id(clip ID)" causes the <par> group to conclude when a designated clip reaches its end. All other clips in the group stop playing at that point, regardless of their playback status or any timing parameters used with them. The designated clip must have a corresponding id value in its source tag.