Anything landing inside a running value curve is refused unless the parameter is cancelled first, and two paths were not cancelling: the chain observer wrote each knob straight onto its AudioParam before rescheduling, and a bent segment read as straight because only the curve exponent was checked, never the via point the timeline actually writes. The first threw NotSupportedError into the console and abandoned the rest of the envelope; the second played a dragged bend as a ramp. Measured against Chrome, in a live context and in an offline one suspended mid-curve: any cancel frees the span, and only a missing cancel is refused. clearParamLane takes the strongest form on purpose, because curve-over-curve refusals were reported with a cancel at the new schedule time already in place and have never reproduced; emit keeps a ramp fallback as the backstop for whatever that mechanism turns out to be. Dynamic carve is what exercises all of it, so it lands here too: - a `gain` primitive, so a carve can match levels as well as carve bands - carve settings collapse to one `strength`, with carveProfile deriving the six numbers that always moved together anyway - analyseCarveDynamics / analyseCarveDuck turn the analysis into envelopes, with a slow release so the bed does not snap back the instant a word ends - worklets are awaited inside attach, so adding a compressor to a carved bed no longer kills its envelopes and freezes every later edit - per-track failure detail in the render's audio stage, which was being discarded Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
@hyperframes/producer
Full HTML-to-video rendering pipeline: capture frames with Chrome's BeginFrame API, encode with FFmpeg, mix audio — all in one call.
Install
npm install @hyperframes/producer
Requirements: Node.js >= 22, Chrome/Chromium (auto-downloaded), FFmpeg
Usage
Render a video
import { createRenderJob, executeRenderJob } from "@hyperframes/producer";
const job = createRenderJob({
inputPath: "./my-composition.html",
outputPath: "./output.mp4",
width: 1920,
height: 1080,
fps: 30,
});
const result = await executeRenderJob(job, (progress) => {
console.log(`${Math.round(progress.percent * 100)}%`);
});
console.log(result.outputPath); // ./output.mp4
Run as an HTTP server
The producer can also run as a render server, accepting render requests over HTTP:
import { startServer } from "@hyperframes/producer";
await startServer({ port: 8080 });
// POST /render with a RenderConfig body
Configuration
RenderConfig controls the render pipeline:
| Option | Default | Description |
|---|---|---|
inputPath |
— | Path to the HTML composition |
outputPath |
— | Output video file path (or directory, for format: "png-sequence") |
width |
1920 | Frame width in pixels |
height |
1080 | Frame height in pixels |
fps |
30 | Frames per second (24, 30, or 60) |
quality |
"standard" |
Encoder preset ("draft", "standard", "high") |
format |
"mp4" |
Output container — "mp4", "webm", "mov", or "png-sequence". See Transparent Video Output below. |
videoFrameFormat |
"auto" |
Source video frame extraction format — "auto", "jpg", or "png". Use "png" for UI recordings, screen captures, and color-sensitive source videos. |
Transparent Video Output
The producer can render HTML compositions to formats that carry a true alpha channel — not chroma key. The same composition that renders an opaque MP4 renders a layerable overlay when you set format.
format |
Codec / pixel format | Alpha | Audio | Use case |
|---|---|---|---|---|
"mp4" (default) |
H.264 (yuv420p) or H.265 + HDR10 | No | AAC | Streaming, social, default deliverable |
"webm" |
VP9 + yuva420p | True alpha | Opus | Web playback as overlay (<video> over background); supported in Chrome, Edge, Firefox |
"mov" |
ProRes 4444 + yuva444p10le | True alpha + 10-bit | AAC | Editor ingest (Premiere, Final Cut Pro, DaVinci Resolve) |
"png-sequence" |
Numbered RGBA PNGs in a directory | Lossless alpha | Sidecar audio.aac |
After Effects / Nuke / Fusion, or pipelines that post-process frames before encoding |
Example
import { createRenderJob, executeRenderJob } from "@hyperframes/producer";
const job = createRenderJob({
inputPath: "./my-composition.html",
outputPath: "./output.webm", // or a directory for "png-sequence"
width: 1080,
height: 1920,
fps: 30,
format: "webm", // "mp4" | "webm" | "mov" | "png-sequence"
});
await executeRenderJob(job);
What "transparent background" means here
The producer captures Chrome screenshots with the page background forced transparent (html, body, [data-composition-id] { background: transparent !important }) and the CDP default background override set to RGBA 0,0,0,0. The captured PNGs carry a real alpha channel and that channel is preserved end-to-end:
- VP9 (
webm) is encoded with-pix_fmt yuva420p,-auto-alt-ref 0,-cpu-used 4by default, andalpha_mode=1metadata. Tune the speed/quality tradeoff withPRODUCER_VP9_CPU_USED(-8to8) or local CLI--vp9-cpu-used. - ProRes 4444 (
mov) is encoded with-pix_fmt yuva444p10le. - PNG sequences are written without re-encoding (zero-padded
frame_NNNNNN.png).
This is not chroma keying. There is no green/blue background to remove and no "key" tolerance to tune — pixels that were transparent in the browser are transparent in the output.
Caveats
- Linux + alpha forces screenshot capture. Chrome's BeginFrame compositor (the default deterministic capture path on Linux headless-shell) does not preserve alpha; the orchestrator falls back to
Page.captureScreenshot, which is slower per frame. macOS and Windows already use screenshot mode by default, so they are unaffected. - HDR + alpha is not supported. Setting
hdr: truetogether with an alpha-capable format logs a warning and falls back to SDR. Useformat: "mp4"for HDR10 output. png-sequencedoes not produce a single muxed file. When the composition contains audio elements, anaudio.aacsidecar is written alongside the PNGs inoutputPath.- Safari + WebM alpha is incomplete. For broad browser playback of an alpha video, ship
format: "mov"to your editor and re-encode for the codec your distribution target supports.
Authoring transparent compositions
Don't paint a fullscreen background in your HTML. The default body background is overridden to transparent automatically — any body { background: ... }, #root { background: ... }, or [data-composition-id] { background: ... } rule is force-overridden during alpha rendering. Backgrounds on inner elements (cards, scenes, components) are kept.
Distributed rendering
For renders too large for a single machine, the producer ships a public set of distributed-render primitives. They are pure functions over local file paths — networking and orchestration live in adapter packages (Temporal, AWS Lambda + Step Functions, Cloud Run Jobs, K8s Jobs).
Plan v2 is recommended for new integrations. It publishes an immutable manifest plus content-addressed artifacts and materializes only each worker's declared dependencies:
import { planV2, renderChunkV2, assembleV2 } from "@hyperframes/producer/distributed";
// Controller-side: produce a v2 manifest + local content-addressed store.
const planResult = await planV2(
projectDir,
{ fps: 30, width: 1920, height: 1080, format: "mp4" },
"/tmp/plan-v2",
);
const chunk = await renderChunkV2("/tmp/plan-v2", 0, "/tmp/chunks/0.mp4");
// Controller-side: stitch chunks into the final deliverable.
await assembleV2("/tmp/plan-v2", ["/tmp/chunks/0.mp4", "/tmp/chunks/1.mp4"], "/tmp/output.mp4");
Cloud adapters should use planV2WithPublisher() so artifacts publish
directly to object storage. The legacy plan() / renderChunk() /
assemble() v1 layout remains supported, and cloud SDKs still interpret an
omitted protocol as v1 for backwards compatibility.
The activity functions plus their result types are also re-exported from @hyperframes/producer so callers that pin the main package don't need a separate subpath import. Supported formats: mp4 SDR, mov ProRes 4444, and png-sequence. webm and HDR mp4 trip a typed FormatNotSupportedInDistributedError — use the in-process renderer (executeRenderJob) for those.
How it works
- Serve — spins up a local file server for the HTML composition
- Capture — opens the page in headless Chrome, seeks frame-by-frame via
HeadlessExperimental.beginFrame(orPage.captureScreenshotfor transparent / non-Linux renders), captures screenshots - Encode — pipes frames through FFmpeg (with GPU encoder detection and chunked concat). Skipped for
format: "png-sequence". - Mix — extracts
<audio>elements and mixes them into the final video. Forpng-sequence, audio is written as anaudio.aacsidecar. - Finalize — applies faststart for streaming-friendly MP4 (no-op for WebM, MOV, and
png-sequence)
Documentation
Full documentation: hyperframes.heygen.com/packages/producer
Related packages
@hyperframes/core— types, parsers, frame adapters@hyperframes/engine— lower-level capture and encode primitiveshyperframes— CLI