## Summary
- Fixes SaveWebM node showing "Error loading image" in Vue nodes mode
- Extracts `isAnimatedOutput`/`isVideoOutput` utility functions from
inline logic in `unsafeUpdatePreviews` so both the litegraph canvas
renderer and Vue nodes renderer can detect video output directly from
execution data
- Uses output-based detection in `imagePreviewStore.isImageOutputs` to
avoid applying image preview format conversion to video files
## Background
In Vue nodes mode, `nodeMedia` relied on `node.previewMediaType` to
determine if output is video. This property is only set via
`onDrawBackground` → `unsafeUpdatePreviews` in the litegraph canvas
path, which doesn't run in Vue nodes mode. This caused webm output to
render via `<img>` instead of `<video>`.
## Before
https://github.com/user-attachments/assets/36f8a033-0021-4351-8f82-d19e3faa80c2
## After
https://github.com/user-attachments/assets/6558d261-d70e-4968-9637-6c24532e23ac
## Test plan
- [x] `pnpm typecheck` passes
- [x] `pnpm lint` passes
- [x] `pnpm test:unit` passes (4500 tests)
┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8943-fix-detect-video-output-from-data-in-Vue-nodes-mode-30a6d73d365081e98e91d6d1dcc88785)
by [Unito](https://www.unito.io)
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Co-authored-by: github-actions <github-actions@github.com>
