According to a first aspect of this specification, there is described a computer-implemented method of tagging video frames. The method comprises generating, using a frame tagging model, a tag for each of a plurality of frames of an animation sequence. The frame tagging model comprises: a first neural network portion configured to process, for each frame of the plurality of frames, a plurality of features associated with the frame and generate an encoded representation for the frame. The frame tagging model further comprises a second neural network portion configured to receive input comprising the encoded representations of each frame and generate output indicative of a tag for each of the plurality of frames.