Surface a clear error when a video format can't be decoded

[dxviie]

Picking a video the browser's decoder rejects — typically an HEVC (H.265) .mov straight off a phone in Firefox (AppleVTDecoder … NS_ERROR_DOM_MEDIA_DECODE_ERR) — used to fail silently: the hidden <video> element fired an error event nobody listened for, so no video UI ever appeared and the studio just sat empty.

What changed

Error handling (src/routes/studio/+page.svelte)

• An onerror handler on the hidden decoder element catches decode/format failures, closes the dead video, and surfaces a clear message: what failed, why (HEVC hint for .mov files), and how to fix it — try another browser, or convert to MP4 (H.264) / WebM via QuickTime, HandBrake or a copy-ready ffmpeg one-liner.
• The message renders two ways from one shared snippet: in the dropzone area when the stage is empty, and as a dismissible card floated over the render (same overlay treatment as the timeline) when the error arrives while something is still on stage — Firefox decodes the first frames of an HEVC .mov before giving up, so the failure often lands mid-scrub with a render still visible. A compact note also appears under the browse button.
• Files dropped on the render that are neither image nor video (they bypass the picker's accept filter) get the same treatment instead of being silently ignored.

Hang fixes

• seekVideo waited for a seeked event that never comes when the decoder dies mid-seek; it now also resolves on error / emptied.
• A decode failure cancels a running frame-sequence export cleanly (and bails before zipping a garbage frame) instead of spinning forever on a dead element.

Docs (src/routes/(site)/help/+page.svelte)

• New "supported formats" entry in the help page's video section documenting the same guidance.

Verification

Driven headlessly (vite dev + Playwright/Chromium): an undecodable .mov from an empty stage shows the dropzone error; a video that renders frames and then errors mid-scrub shows the overlay card with the last render kept underneath, timeline removed, and dismiss clearing everything; a .txt drop shows "can't read"; a valid webm afterwards clears the error and loads the pipeline as before. svelte-check, eslint, prettier and all 263 unit tests pass.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Ng25H1kphEz6dXXevJC8R5

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Generated by Claude Code

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