Alibaba Researchers Propose I2VGen-xl: A Cascaded Video Synthesis AI Model which is Capable of Generating High-Quality Videos from a Single Static Image

Researchers from Alibaba, Zhejiang University, and Huazhong University of Science and Technology have come together and introduced a groundbreaking video synthesis model, I2VGen-XL, addressing key challenges in semantic accuracy, clarity, and spatio-temporal continuity. Video generation is often hindered by the scarcity of well-aligned text-video data and the complex structure of videos. To overcome these obstacles, the researchers propose a cascaded approach with two stages, known as I2VGen-XL.

The I2VGen-XL overcomes the obstacle in two stages:

The base stage focuses on ensuring coherent semantics and preserving content by utilizing two hierarchical encoders. A fixed CLIP encoder extracts high-level semantics, while a learnable content encoder captures low-level details. These features are then integrated into a video diffusion model to generate videos with semantic accuracy at a lower resolution. 

The refinement stage enhances video details and resolution to 1280×720 by incorporating additional brief text guidance. The refinement model employs a distinct video diffusion model and a simple text input for high-quality video generation.

One of the main challenges in text-to-video synthesis currently is the collection of high-quality video-text pairs. To enrich the diversity and robustness of I2VGen-XL, the researchers collect a vast dataset comprising around 35 million single-shot text-video pairs and 6 billion text-image pairs, covering a wide range of daily life categories. Through extensive experiments, the researchers compare I2VGen-XL with existing top methods, demonstrating its effectiveness in enhancing semantic accuracy, continuity of details, and clarity in generated videos.

The proposed model leverages Latent Diffusion Models (LDM), a generative model class that learns a diffusion process to generate target probability distributions. In the case of video synthesis, LDM gradually recovers the target latent from Gaussian noise, preserving the visual manifold and reconstructing high-fidelity videos. I2VGen-XL adopts a 3D UNet architecture for LDM, referred to as VLDM, to achieve effective and efficient video synthesis.

The refinement stage is pivotal in enhancing spatial details, refining facial and bodily features, and reducing noise within local details. The researchers analyze the working mechanism of the refinement model in the frequency domain, highlighting its effectiveness in preserving low-frequency data and improving the continuity of high-definition videos.

In experimental comparisons with top methods like Gen-2 and Pika, I2VGen-XL showcases richer and more diverse motions, emphasizing its effectiveness in video generation. The researchers also conduct qualitative analyses on a diverse range of images, including human faces, 3D cartoons, anime, Chinese paintings, and small animals, demonstrating the model’s generalization ability.

In conclusion, I2VGen-XL represents a significant advancement in video synthesis, addressing key challenges in semantic accuracy and spatio-temporal continuity. The cascaded approach, coupled with extensive data collection and utilization of Latent Diffusion Models, positions I2VGen-XL as a promising model for high-quality video generation from static images. The model has also identified limitations, including challenges in generating natural and free human body movements, limitations in generating long videos, and the need for improved user intent understanding.

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