Some filters can not be applied to a track or the entire timeline. It is only a very few that are prevented, but Crop is one of them. That is because this crop filter is like a “source edge cropping.” There are other kinds of cropping people would like such as one that leaves the original pixels in their place and pads with transparent black. This Crop filter is one that understands the source clip’s maximum resolution and will let you remove from edges while taking advantage of a clip or picture resolution that is larger than your project - 1920 x 1080, for example. Think about it in terms of a digital photo that is usually several megapixels higher resolution than a video. You would not want to scale it to fit within the video frame, remove edges, and then scale it up to fill as much of the frame as possible. You would not be taking advantage of all the possible resolution of the source clip/photo. So, Crop is designed to work with the source resolution to be optimize this situation. However, it is currently incompatible with the more abstract sources of “track” and “timeline”. This may change in the future, but we shall see.