Format matrix: WebM fallback + transparent video (issue 06) - #9
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Probe encoder capabilities at export-dialog open (mediabunny canEncodeVideo,
cached per session); every decision over the probed plain data is a pure core
rule: MP4/H.264 default, honest WebM/VP9 fallback ("this browser can't encode
MP4", never silent), transparency forces WebM + alpha 'keep' and is offered
only when the alpha probe passes and the Stage background is transparent, and
resolution presets respect the probed encoder maximums (4K hidden when the
hardware encoder tops out lower).
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The transparent branch of selectVideoFormat gated only on "alpha encodable" while the ladder clamped against the opaque VP9 max — so a transparent choice could pair with an empty preset list, and an offered preset could exceed what alpha-preserving VP9 (a stricter encoder config) actually accepts. Replace the vp9Alpha boolean with a probed vp9AlphaMaxDimension ceiling and key both the format selection and the resolution clamp on it when the export is transparent.
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| ) : videoPresets.length === 0 ? ( | ||
| <p className="text-[11px] leading-snug text-muted"> | ||
| This browser can't encode video (no MP4 or WebM encoder). | ||
| </p> |
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Empty presets misreport encoder
Medium Severity
When capabilities are loaded and selectVideoFormat returns a valid choice but availableVideoHeightPresets filters out every height (e.g. a wide match-frame aspect with a modest encoder max), the resolution section still says the browser cannot encode MP4 or WebM, even though the format row may show MP4 or WebM as available.
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| let cancelled = false | ||
| void probeVideoEncoderCapabilities().then((probed) => { | ||
| if (!cancelled) setCapabilities(probed) | ||
| }) |
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Probe rejection stalls dialog
Medium Severity
The export panel only handles a fulfilled probeVideoEncoderCapabilities promise. If the probe rejects, capabilities never leave null, so video mode can show “Checking encoder support…” indefinitely and keep export disabled even after the probe has finished.
Additional Locations (1)
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Summary
scene/encoder-capabilities.ts, mediabunnycanEncodeVideo, cached per session) and reduces them to plain data; every decision derived from the probe is a pure, Vitest-covered core rule (16 new tests, TDD red-first).alpha: 'keep'and is only offered when the alpha probe passes AND the Stage background is transparent (mirroring the transparent-PNG rule), with the Safari/desktop-editors caveat surfaced.scene.backgroundre-assert for transparent captures (an animated stage colour would rebake it mid-encode), and per-frame encode-canvas clear so semi-transparent pixels don't accumulate prior frames.Test plan
selectVideoFormat,transparentVideoAvailable,availableVideoHeightPresets,resolveVideoEncodewebm/alpha,.webmfilename).scratch/animation-video-export/evidence/06/, system Chrome via Playwright): MP4 · H.264 default at dialog open; transparency check flips format to WebM · VP9 with caveat; exported transparent WebM decoded frame asserts corner alpha 0 / center 255 and composites correctly over an orange page background; opaque default downloads.mp4; transparency option absent for a gradient backgroundmp4Fallbackdialog state not exercisable live in Chrome (it encodes H.264) — rule and label covered by Vitest/typecheckNote
Medium Risk
Touches the multi-second video encode path and format/transparency gating; mistakes could cause failed encodes or silent wrong format, but logic is heavily unit-tested and avoids starting doomed exports.
Overview
Adds issue 06 video format matrix: MP4/H.264 stays default; browsers without H.264 get WebM/VP9 with an explicit “can't encode MP4” warning (
mp4Fallback). Transparent video forces WebM + VP9alpha: 'keep', only when the alpha encoder probe succeeds and the stage background is transparent (same idea as transparent PNG).Core gains probed
VideoEncoderCapabilities, pure helpers (selectVideoFormat,transparentVideoAvailable,encoderMaxDimension,availableVideoHeightPresets),transparentonVideoExportRequest, andresolveVideoEncode(format, transparent)with VP9 + alpha mode. Resolution presets are encoder-aware (e.g. 4K hidden when max dimension is too low; separate alpha VP9 ceiling).Scene: new
probeVideoEncoderCapabilities(mediabunnycanEncodeVideo, session cache); Exporter muxes MP4 or WebM, applies alpha-0 clear / per-framescene.backgroundnulling and encode-canvasclearRectfor transparent WebM.Export panel probes on open, disables video until probe completes, shows format/fallback/transparent UI, and builds the updated video request.
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