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Miguel Ángel
95d2a949b7
Animated media volume (GSAP/JS fades) dropped the audio track entirely for dense fades. The 60 Hz timeline probe emits 100-300 keyframes for a multi-second fade, which were folded into an FFmpeg `volume` expression nesting one `if(lt(t,...))` per keyframe. Past ~95 nested levels (build-dependent, lower on some Linux ffmpeg builds) the expression overflows FFmpeg's evaluator, fails filter-graph init, fails the whole mix, and the muxer omits audio — so a `data-volume="0"` fade-in rendered with no audio at all (follow-up to #1066; this is why #1064's own scenario regressed once the fade was dense enough). Apply volume automation as sample-accurate gain, layered so audio is never lost: 1. Primary: bake the envelope into the prepared PCM samples in-process (audioVolumeEnvelope.ts). The track WAV is always pcm_s16le/48k/stereo; multiply its samples by the interpolated envelope and atomically rename the result into place, then mix at unity. No expression, no keyframe ceiling, exact at every sample, and the downstream ffmpeg amix/AAC encode is untouched so golden baselines only change where a fade is applied. The RIFF parser scans chunks order-independently and accepts only 16-bit PCM, falling back otherwise. The output is written to a random-named sibling and renamed, so a crash can't leave a truncated WAV and there's no predictable-path write. 2. Fallback: RDP-bounded ffmpeg `volume` expression (0.5% tolerance, capped at 32 segments) for the rare case a WAV is not 16-bit PCM. 0.5% keeps the rendered envelope within ~0.2 dB of the source curve. 3. Backstop: if an automated mix still fails, retry once at base volume and surface the degradation rather than dropping the track. This mirrors how OSS NLEs render automation (sample-level gain): MoviePy, Kdenlive/Shotcut (MLT), Remotion. Verified end-to-end: a 297-keyframe fade that rendered with no audio now bakes all 297 keyframes sample-accurately. Adds unit tests for sample-accurate gain, track-start offset, base/tail holds, thousands of keyframes, order-independent chunk parsing, and format rejection, plus mixer regression tests for bounded nesting and the base-volume backstop.
@hyperframes/engine
Seekable web-page-to-video rendering engine built on Puppeteer and FFmpeg.
Framework-agnostic: works with GSAP, Lottie, Three.js, CSS animations, or any web content that implements the window.__hf seek protocol.
Install
npm install @hyperframes/engine
Requirements: Node.js >= 22, Chrome/Chromium (auto-downloaded by Puppeteer), FFmpeg
What it does
The engine opens your HTML composition in a headless Chrome instance, seeks frame-by-frame using Chrome's HeadlessExperimental.beginFrame API, captures screenshots, and encodes them into video with FFmpeg.
Key services
| Service | Description |
|---|---|
| browserManager | Launches and pools headless Chrome instances (chrome-headless-shell) |
| frameCapture | Manages capture sessions — seek, screenshot, buffer lifecycle |
| screenshotService | BeginFrame-based capture with CDP (Chrome DevTools Protocol) |
| chunkEncoder | FFmpeg encoding with chunked concat, GPU detection, faststart |
| streamingEncoder | Pipe frames to FFmpeg in real time (no intermediate PNGs on disk) |
| audioMixer | Parse <audio> elements and mix audio tracks via FFmpeg |
| videoFrameExtractor | Extract frames from <video> elements for compositing |
| parallelCoordinator | Split frame ranges across worker processes |
| fileServer | Serve local HTML files to the browser via Hono |
Usage
import {
acquireBrowser,
releaseBrowser,
createCaptureSession,
initializeSession,
captureFrame,
closeCaptureSession,
} from "@hyperframes/engine";
// 1. Launch browser
const browser = await acquireBrowser({ captureMode: "beginFrame" });
// 2. Open a capture session
const session = createCaptureSession({
browser: browser.browser,
url: "http://localhost:3000/my-composition.html",
width: 1920,
height: 1080,
fps: 30,
});
await initializeSession(session);
// 3. Capture frames
for (let i = 0; i < totalFrames; i++) {
await captureFrame(session, i, `/tmp/frames/frame-${i}.png`);
}
// 4. Clean up
await closeCaptureSession(session);
await releaseBrowser(browser);
Most users should use @hyperframes/producer or the hyperframes CLI instead of calling the engine directly.
Documentation
Full documentation: hyperframes.heygen.com/packages/engine
Related packages
@hyperframes/core— types, parsers, frame adapters@hyperframes/producer— high-level render pipeline built on this enginehyperframes— CLI