1. A computer-implemented method for interpolating user-defined format conversion constraints based on key frames, the method comprising: receiving a selection of a first frame of an input sequence of images and a selection of a second frame of the input sequence of images, wherein each of the first frame and the second frame is designated as a key frame, wherein the input sequence of images includes an intervening frame disposed between the first frame and the second frame; receiving a first user-defined format conversion constraint defining a first feature in the first frame and a second user-defined format conversion constraint defining the first feature in the second frame, wherein a characteristic of the first feature in the second frame is different than a corresponding characteristic of the first feature in the first frame, wherein the first feature in the first frame and the first feature in the second frame are transformed based on a first transformation factor; interpolating the characteristic of the first feature in the intervening frame disposed between the first frame and the second frame in the sequence of images based on the characteristic of the first feature in the first frame and the characteristic of the first feature in the second frame and by operation of one or more processors, thereby interpolating the first and second user-defined format conversion constraints, wherein the interpolated characteristic is not user-specified; transforming the first feature in the intervening frame based on the first transformation factor and the interpolated characteristic of the first feature in the intervening frame; and transforming at least one non-feature region in the intervening frame using a non-linear warp function generated by optimizing an energy equation, wherein the energy equation is generated based on the interpolated characteristic, wherein the first feature in the intervening frame is not transformed based on the non-linear warp function, wherein the non-linear warp function is configured to, when applied to the input sequence of images, map from the input sequence of images to an output sequence of images.