When training i2v models without specifying image_column, automatically extract
and use first frames from training videos as conditioning images. This includes:
- Add load_images_from_videos() utility function to extract and cache first frames
- Update BaseI2VDataset to support auto-extraction when image_column is None
- Add validation and warning message in Args schema for i2v without image_column
The first frames are extracted once and cached to avoid repeated video loading.
- Add dataset implementations for text-to-video and image-to-video
- Include bucket sampler for efficient batch processing
- Add utility functions for data processing
- Create dataset package structure with proper initialization
