Which SMIL Attributes Set Transition Duration and Direction?

Synchronized Multimedia Integration Language (SMIL) provides specialized transition effects to blend media elements smoothly over time. Controlling the timing, speed, and geometric movement of these visual effects relies on a core set of dedicated XML attributes. This article explains the primary attributes used to define how long a SMIL transition lasts and the specific direction or pattern across the screen it follows.

Controlling Duration with the dur Attribute

The length of time a transition takes to complete is primarily governed by the dur attribute. When applied to a <transition> element or directly to a media object using transition filters, dur defines the active clock duration of the visual change.

• Syntax and Values: The dur attribute accepts standard SMIL clock values, such as seconds (e.g., dur="2.5s") or minutes and seconds (e.g., dur="00:03").
• Behavior: If dur is omitted, the player defaults to the implementation-defined duration or inherits timing parameters from the parent timeline. Setting an explicit dur ensures precise synchronization with accompanying audio or concurrent visual tracks.

Defining Geometric Direction with subtype and direction

SMIL splits direction control into two main attributes: subtype for geometric orientation and direction for the temporal progression of the wipe.

The subtype Attribute

While the type attribute defines the broad family of the transition (such as barWipe, irisWipe, or slideWipe), the subtype attribute specifies the exact axis and vector of movement. Common values include:

• leftToRight and rightToLeft for horizontal wipes.
• topToBottom and bottomToTop for vertical wipes.
• clockwise and counterClockwise for radial transitions like clockWipe or pinWheelWipe.
• cornersIn, cornersOut, topRight, or bottomLeft for box and diagonal transitions.

The direction Attribute

The direction attribute modifies the forward or backward execution of the transition pattern. It accepts two primary values:

• forward: The transition reveals the new media according to the standard geometric path defined by the type and subtype. This is the default setting.
• reverse: The transition inverts the geometric progression, wiping the effect in the opposite direction without requiring a change to the underlying subtype.

Fine-Tuning Boundaries with startProgress and endProgress

To control partial transitions or alter where a directional movement begins and ends, SMIL uses startProgress and endProgress:

• startProgress: Takes a fractional value between 0.0 and 1.0 defining the starting state of the transition (default is 0.0).
• endProgress: Takes a fractional value between 0.0 and 1.0 defining the completion point (default is 1.0).

Using these attributes alongside dur, subtype, and direction allows developers to truncate the path of a directional wipe or create faster, specialized segment transitions across multimedia presentations.