Extrapolate and Hold
When you use standard keyframes, you always have a starting keyframe and an ending keyframe that are fixed at the start of the effect and the end of the effect. You cannot move or delete the starting keyframe and the ending keyframe. With advanced keyframes, you do not need to set a starting keyframe or an ending keyframe, and you can move or delete them if you want to.
 | |
To keep the Avid editing application from creating starting and ending
keyframes when you promote an effect, deselect Automatic Start and End
Keyframes in the Effect Editor entry in the Settings scroll list.
|
In a keyframe graph, the first keyframe and the last keyframe are the bracketing keyframes for the parameter. The Avid editing application determines parameter values beyond the bracketing keyframes using either Extrapolate or Hold.
With Extrapolate enabled, the Avid editing application extrapolates — that is, estimates more values for — the parameter values at the start and end of an effect using the values at the bracketing keyframes. Parameter values continue to change over time. The application calculates new values using the interpolation option in effect for that parameter.
For example, if the parameter value between the last two keyframes increases as the end of the effect approaches, the parameter value continues to increase until the end of the effect. Similarly, if the first keyframe is not at the very beginning of the clip, the Avid editing application extrapolates the parameter value from the start of the effect up to the first keyframe.
With Hold enabled, the application uses only the parameter values at the bracketing keyframes to set values at the start and end of the effect. The parameter values hold steady — that is, are the same — from the start of the effect to the first keyframe, and again from the last keyframe to the end of the effect.
Extrapolate and Hold are useful any time you slip keyframes or align keyframes in such a way that a bracketing keyframe falls within the effect, or if you are using fixed keyframes for a parameter and you trim in or trim out the effect so that a bracketing keyframe falls within the effect.
| |
The Extrapolate or Hold setting remains in effect if you trim in or trim out
the effect.
|
In either case, you do not have an explicitly defined value outside the bracketing keyframes. Extrapolate and Hold can save you the trouble of individually setting new values for each parameter whenever you make changes to the position of keyframes or the length of the effect.
When you select Extrapolate, the application estimates more values for the parameter before and after the bracketing keyframes using the values at the bracketing keyframes. Parameter values continue to change over time. The application calculates new values using the interpolation option in effect for that parameter.
When you select Hold, the application uses only the parameter values at the bracketing keyframes to set values before and after the bracketing keyframes. The parameter values are the same from the start of the effect to the first keyframe, and again from the last keyframe to the end of the effect.
| |
As a result of slipping the keyframes in the previous examples, the last
keyframe indicator has moved out of the keyframe graph view but is still
present and is still the bracketing keyframe. The keyframe indicator visible
at the right edge of the keyframe graph (the third keyframe indicator) is not
a bracketing keyframe. Therefore, the parameter values in effect from the
third keyframe to the end of the effect are calculated along the curve
between the third keyframe and the last (bracketing) keyframe.
|
| |
You set Extrapolate and Hold independently for each parameter in an
effect. The default condition is Hold.
|
To set Extrapolate or Hold for a parameter:
|
|
Right-click (Windows) or Ctrl+Shift+click (Macintosh) the keyframe
track, and select Extrapolate or Hold.
|
The display changes to reflect the new setting.
