Zero4D: Training-Free 4D Video Generation From Single Video
Using Off-the-Shelf Video Diffusion

Reconstruction pipeline of Zero4D: (a) Key frame generation step: (a1) Given a fixed-viewpoint grayscale input video, we generate synchronized multi-view videos using the I2V diffusion model. (a2) We first synthesize key frames of the 4D grid through diffusion sampling, guided by warped views. (a3) Next, we generate the end-view video frames using a process similar to (a2), guided by warped views. (a4) Finally, we complete the rightmost column using diffusion-based interpolation sampling. (b) Spatio-temporal bidirectional interpolation step: Starting from the initial noise in (a4), we denoise the remaining frames through a camera-axis interpolation denoising step. At this stage, the noisy frame x_t[:, i] is updated based on edge frames along the camera axis. Then, the time-axis interpolation step follows, where perturbed frames are denoised through interpolation along the time axis of the 4D grid, conditioned on edge frames in the time axis. The spatio-temporal bidirectional sampling alternates between camera-axis interpolation and time-axis interpolation, progressively refining noisy latents into clean frames. Through this process, we obtain globally coherent spatio-temporal 4D grid videos.

For Novel view generation, we compare with Generative Camera Dolly, and Stable Video 4D which employs the same input frame as ours.