### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### The Feature

Please add native support for OpenAI-compatible `video_url` message content when using Gemini models through LiteLLM (`vertex_ai/...` and `gemini/...` paths).

When a request contains:

```json { "type": "video_url", "video_url": { "url": "data:video/mp4;base64,..." } } ```

LiteLLM should convert it into a Gemini-compatible media part (for example via `file_data` + MIME type), similar to how other multimodal content is normalized.

Requested behavior:

1. Accept `video_url` in OpenAI chat content arrays for Gemini routes. 2. Support both `data:` URLs and regular public URLs. 3. Infer MIME type when possible and allow explicit override. 4. Preserve optional metadata (e.g. `video_metadata`) if provided. 5. Return a clear validation error if conversion is impossible (instead of silently ignoring media).

### Motivation, pitch

We rely on OpenAI-compatible payloads across multiple providers. For Gemini models in LiteLLM, `video_url` is currently not recognized in practice, so video input is effectively lost.

Observed result: - Model responds as …