1. the VideoPlaybackBehaviour.cs script that is referred to in this thread is located in the VideoPlayback sample project, which you can download from:
Another useful script to look at is the VideoPlayerHelper.cs, in the same sample project. Note that all the sample scripts can be found under the Assets directory.
2. the topic in this thread is about how to resize the plane on which the video rectangle texture is applied to; as you can imagine, this is related to a piece of sample application logic, and not a Vuforia API or Vuforia -specific feature; in fact, if you analyze the topic closely, the basic question here is essentially about "how to rescale a textured plane in Unity"; this is in fact a general Unity-programming and C# programming question, not a Vuforia-specific issue; in fact, the plane on top of which the videoplayback texture is applied is a standard Unity plane, and you control its scale and size with Unity API and with geenral C# programming, as shown in the example snippet below, for instance:
Vector3(-0.1f, 0.1f, 0.1f * aspect);
Also, the computation of the aspect ratio (the "aspect" variable) is also based on a width and height parameters of the loaded video file (again, this does not come from the Vuforia API or from a Vuforia feature, as you will realize by looking at the sample code that handles the video file width and height in the sample code, in particular, by looking at the VideoPlayerHelper.cs script).
See also Unity Transforms API reference: