Abstract: Methods and systems using photorealistic avatars to provide live interaction. Several groups of innovations are described. In one such group, trajectory information included with the avatar model makes the model 4D rather than 3D. In another group, a fallback representation is provided with deliberately-low quality. In another group, avatar fidelity is treated as a security requirement. In another group, avatar representation is driven by both video and audio inputs, and audio output depends on both video and audio input. In another group, avatar representation is updated while in use, to refine representation by a training process. In another group, avatar representation uses the best-quality input to drive avatar animation when more than one input is available, and swapping to a secondary input while the primary input is insufficient. In another such group, the avatar representation can be paused or put into a standby mode.