---
title: "interpolateBetween(_:withWeight:)"
framework: Professional Video Applications
role: symbol
role_heading: Instance Method
platforms: [fxplug 4.0+]
path: "professional_video_applications/fxcustomparameterinterpolation_v2/interpolatebetween(_:withweight:)"
---

# interpolateBetween(_:withWeight:)

Returns a new parameter value which has been calculated by interpolating between                 two key values.

## Declaration

```swift
func interpolateBetween(_ rightValue: any NSCopying & NSSecureCoding & NSObjectProtocol, withWeight weight: Float) -> any NSCopying & NSSecureCoding & NSObjectProtocol
```

## Parameters

- `rightValue`: The value of the custom parameter at the keypoint to the right of the current time in the timeline.
- `weight`: A floating-point value between 0 and 1 representing the weight of the keyframe to the right of the current time vs the keyframe to the left of the current time. A weight of 0 means the same value as the keyframe to the left; a weight of 1 means the same value as the keyframe to the right.

## Return Value

Return Value A new custom parameter value.

## Discussion

Discussion This plug-in method is called by the host application when the user has added keyframes to a custom parameter, and the application needs to know the value of the parameter between keyframes. This may be when the application is rendering a frame between keyframes, or when the plugin requests the value of its parameter at a time between keyframes, or when the application displays UI.

## See Also

### Instance Methods

- [isEqual(_:)](professional_video_applications/fxcustomparameterinterpolation_v2/isequal(_:).md)