Title: Learning Implicit Scale Conditioned Memory Compensation for Talking Head Generation. Abstract: Talking head video generation aims to animate the pose and expression of a person in a target driving video using motion information contained in the video, while maintaining a person's identity in a given still source image. Highly dynamic and complex motions in the driving video cause ambiguous generation from the source image, because the still source image cannot provide sufficient appearance information for occluded regions or delicate expressions, which severely produces artifacts and significantly degrades the generation quality. However, existing works mainly focus on learning more accurate motion estimation and representation in 2D and 3D, and they ignore the facial structural prior in addressing the facial ambiguities. Therefore, effective handling of the ambiguities in the dramatic appearance changes of the source to largely improve facial details and completeness in generation still remains barely explored. To this end, we propose a novel implicit scale conditioned memory compensation network (MCNet) for high-fidelity talking head generation. Specifically, considering human faces are symmetric and structured, we aim to automatically learn a representative global facial memory bank from all training data as a prior to compensate for the facial generation features. Each face in the source image contains a scale that can be reflected in detected facial keypoints. To better query the learned global memory, we further propose to learn implicit scale representations from the discrete keypoints, which can be used to condition on the query of the global memory, to obtain scale-aware memory for the feature compensation. Extensive experiments from quantitative and qualitative perspectives demonstrate that MCNet can learn representative and complementary facial memory, and can clearly outperform previous state-of-the-art methods on VoxCeleb1 and CelebV datasets. 