VideoMerge: Towards Training-free Long Video Generation

Long video generation remains a challenging and compelling topic in computer vision. Diffusion based models, among the various approaches to video generation, have achieved state of the art quality with their iterative denoising procedures. However, the intrinsic complexity of the video domain renders the training of such diffusion models exceedingly expensive in terms of both data curation and computational resources. Moreover, these models typically operate on a fixed noise tensor that represents the video, resulting in predetermined spatial and temporal dimensions. Although several high quality open-source pretrained video diffusion models, jointly trained on images and videos of varying lengths and resolutions, are available, it is generally not recommended to specify a video length at inference that was not included in the training set. Consequently, these models are not readily adaptable to the direct generation of longer videos by merely increasing the specified video length. In addition to feasibility challenges, long-video generation also encounters quality issues. The domain of long videos is inherently more complex than that of short videos: extended durations introduce greater variability and necessitate long-range temporal consistency, thereby increasing the overall difficulty of the task. We propose VideoMerge, a training-free method that can be seamlessly adapted to merge short videos generated by pretrained text-to-video diffusion model. Our approach preserves the model's original expressiveness and consistency while allowing for extended duration and dynamic variation as specified by the user. By leveraging the strengths of pretrained models, our method addresses challenges related to smoothness, consistency, and dynamic content through orthogonal strategies that operate collaboratively to achieve superior quality.

Towards Chunk-Wise Generation for Long Videos

Generating long-duration videos has always been a significant challenge due to the inherent complexity of spatio-temporal domain and the substantial GPU memory demands required to calculate huge size tensors. While diffusion based generative models achieve state-of-the-art performance in video generation task, they are typically trained with predefined video resolutions and lengths. During inference, a noise tensor with specific resolution and length should be specified at first, and the model will perform denoising on the entire video tensor simultaneously, all the frames together. Such approach will easily raise an out-of-memory (OOM) problem when the specified resolution and/or length exceed a certain limit. One of the solutions to this problem is to generate many short video chunks autoregressively with strong inter-chunk spatio-temporal relation and then concatenate them together to form a long video. In this approach, a long video generation task is divided into multiple short video generation subtasks, and the cost of each subtask is reduced to a feasible level. In this paper, we conduct a detailed survey on long video generation with the autoregressive chunk-by-chunk strategy. We address common problems caused by applying short image-to-video models to long video tasks and design an efficient $k$-step search solution to mitigate these problems.