Virtual Character Definition and Animation within the MPEG-4 Standard - 3D Modeling and Animation: Synthesis and Analysis Techniques for the Human Body - page 54

consistency of the data over different decoder implementation, the interpolation
schemes were also standardized.
For real-time purposes, a linear interpolation is used for the translation and scale
components and a spherical linear quaternion interpolation is used for the rotation
and scaleOrientation components.

Animation frame

In an SMS textual or binary format, for each key frame, two types of information
are defined: a vector corresponding to the animation mask, called
animationMaskVector, which indicates the components of the geometrical
transformation to be updated in the current frame; and a vector corresponding
to the animation values called animationValueVector which specifies the new
values of the components to be updated.
Let us describe the content of each of these vectors. For the exact syntax, one
can refer to the ISOIEC (2003).

• animationMaskVector

In the animation mask of a key-frame, a positive integer KeyFrameIndex
indicates to the decoder the number of frames which have to be obtained
by temporal interpolation. If this number is zero, the decoder sends the
frame directly to the animation engine. Otherwise, the decoder computes
n intermediate frames (n= KeyFrameIndex ) and sends them to the anima-
tion engine, together with the content of the received key-frame.
Some bones or muscles of the SMS virtual character may not be animated
in all frames. The boneIDs and muscleIDs of the updated bones and
muscles, respectively, are parts of the animationMaskVector . In addition,
animationMaskVector contains the animation mask of each bone,
boneAnimationMaskVector , and the animation mask of each muscle,
muscleAnimationMaskVector . These vectors are detailed below.

•

animationValueVector
The animationValueVector contains the new values of each bone and
muscle geometric transformation that have to be transmitted and it is
obtained by concatenation of all the boneAnimationValueVector and
muscleAnimationValueVector fields.
For compression efficiency, SMS stream specifications limit the maximum
number of bones and muscle nodes to 1,024 each. These bone and muscle