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title Rendering
description Render compositions to MP4, MOV, or WebM locally or in Docker.

Render your Hyperframes compositions to MP4, MOV, or WebM with the CLI. The rendering pipeline is frame-by-frame and seek-driven — see Deterministic Rendering for how this works under the hood.

Getting Started

Run the diagnostics command to check for required dependencies: 
```bash Terminal
npx hyperframes doctor
```

Expected output:

```
✓ Node.js    v22.x
✓ FFmpeg      7.x
✓ FFprobe     7.x
✓ Chrome      (bundled)
✓ Docker      available
```
Before rendering, preview your composition in the browser to verify it looks correct: 
```bash Terminal
npx hyperframes preview
```
Run the render command from your project directory: 
```bash Terminal
npx hyperframes render --output output.mp4
```

Expected output:

```
⠋ Rendering composition "root" (30fps, standard quality)
✓ Captured 240 frames in 8.2s
✓ Encoded to output.mp4 (8.0s, 1920x1080, 4.2MB)
```

Rendering Modes

### Local Mode (default) 
Uses Puppeteer (bundled Chromium) and your system's FFmpeg. Fast for iteration during development.

**Requires:** FFmpeg installed on your system. See [Troubleshooting](/guides/troubleshooting) if FFmpeg is not found.

```bash Terminal
npx hyperframes render --output output.mp4
```

**Pros:**
- Fast startup, no container overhead
- Can use your system GPU for Chrome/WebGL capture by default
- Can use your system GPU for hardware-accelerated encoding (with `--gpu`)
- Best for iterative development

**Cons:**
- Output may vary across platforms due to font and Chrome version differences
- Not suitable for CI/CD pipelines that require reproducibility
### Docker Mode 
[Deterministic](/concepts/determinism) output with an exact Chrome version and font set. Use this for production renders and CI pipelines.

**Requires:** Docker installed and running.

```bash Terminal
npx hyperframes render --docker --output output.mp4
```

**Pros:**
- Identical output on every platform — same Chrome, same fonts, same FFmpeg
- The same pipeline used in production
- Ideal for CI/CD and automated workflows

**Cons:**
- Slower startup due to container initialization
- Browser capture stays on the deterministic software-GL path
- GPU encoding requires Docker host GPU passthrough and is not cross-platform on Docker Desktop

<Note>
  Docker mode uses `chrome-headless-shell` with [BeginFrame](/concepts/determinism#how-it-works) control for frame-perfect, deterministic capture.
</Note>

When to Use Each Mode

Scenario Recommended Mode
Local development and iteration Local
CI/CD pipeline Docker
Sharing renders with a team Docker
Quick preview export Local
AI agent-driven rendering Docker
Benchmarking performance Local

Options

Flag Values Default Description
--output path renders/<name>.mp4 Output file path
--format mp4, mov, webm, png-sequence mp4 Output format (see Transparent Video below)
--fps 24, 30, 60 30 Frames per second
--quality draft, standard, high standard Encoding quality preset
--crf 0–51 — Override CRF (lower = higher quality). Cannot combine with --video-bitrate
--video-bitrate e.g. 10M, 5000k — Target bitrate encoding. Cannot combine with --crf
--video-frame-format auto, jpg, png auto Source video frame extraction format. Use png for UI recordings, screen captures, and color-sensitive source videos
--workers 1-8 or auto auto Parallel render workers (see Workers below)
--max-concurrent-renders 1-10 2 Max simultaneous renders via the producer server (see Concurrent Renders below)
--gpu — off GPU encoding (NVENC, VideoToolbox, AMF, VAAPI, QSV)
--browser-gpu / --no-browser-gpu — on locally, off in Docker Use or opt out of host GPU acceleration for local Chrome/WebGL capture
--hdr — off Force HDR output even if no HDR sources are detected (MP4 only). See HDR Rendering
--sdr — off Force SDR output even if HDR sources are detected
--docker — off Use Docker for deterministic rendering
--quiet — off Suppress verbose output

Quality and Encoding

The --quality flag selects a preset that controls the H.264 CRF (Constant Rate Factor) and encoder speed:

Preset CRF x264 Preset Best For
draft 28 ultrafast Quick previews, iteration
standard 18 medium General use — visually lossless at 1080p
high 15 slow Final delivery, near-lossless quality

For finer control, use --crf or --video-bitrate to override the preset:

# Near-lossless quality (CRF 15 = very high quality, large file)
npx hyperframes render --crf 15 --output pristine.mp4

# Target a specific bitrate (useful for size-constrained delivery)
npx hyperframes render --video-bitrate 10M --output controlled.mp4

Tip: The default standard preset (CRF 18) is visually lossless at 1080p — most people cannot distinguish it from the source. Use --quality draft for faster iteration, or --quality high / --crf 10 when file size is no concern.

For UI recordings, screen captures, or other source videos where saturated interface colors matter, pass --video-frame-format png to extract source video layers as PNG before browser capture. The default auto mode preserves the historical behavior: alpha-capable sources use PNG, opaque sources use JPG.

GPU Acceleration

Hyperframes has two separate GPU acceleration surfaces:

  • --gpu uses a hardware video encoder in FFmpeg when one is available. Supported backends include VideoToolbox on macOS, NVENC on NVIDIA systems, AMD AMF on Windows, VAAPI on Linux, and Intel QSV on supported Windows/Linux hosts.
  • Browser GPU uses the host GPU for local Chrome/WebGL capture. It is enabled automatically for local renders and disabled in Docker. Use --no-browser-gpu to opt out.
# Add hardware FFmpeg encoding to the default local browser-GPU render
npx hyperframes render --gpu --output encoded-fast.mp4

# Opt out of hardware Chrome/WebGL capture
npx hyperframes render --no-browser-gpu --output software-browser.mp4

# Use browser GPU plus hardware FFmpeg encoding
npx hyperframes render --gpu --output gpu.mp4

Browser GPU capture is local-mode only. It maps to platform-native Chrome GPU backends: Metal on macOS, D3D11 on Windows, and EGL on Linux. Use --no-browser-gpu or Docker mode when exact cross-machine reproducibility matters more than local render speed.

Workers

Each render worker launches a separate Chrome browser process to capture frames in parallel. More workers can speed up rendering, but each one consumes ~256 MB of RAM and significant CPU.

Default behavior

By default, Hyperframes uses half of your CPU cores, capped at 4:

Machine CPU cores Default workers
MacBook Air (M1) 8 4
MacBook Pro (M3) 12 4 (capped)
4-core laptop 4 2
2-core VM 2 1

This is intentionally conservative. Each worker spawns its own Chrome process, so the per-worker overhead is significant. Fewer workers avoids resource contention with FFmpeg encoding and your other applications.

Choosing a worker count

# Explicit worker count
npx hyperframes render --workers 1 --output output.mp4

# Let Hyperframes pick based on your CPU
npx hyperframes render --workers auto --output output.mp4

# Maximum parallelism (use with caution on laptops)
npx hyperframes render --workers 8 --output output.mp4
Start with the default. If renders feel slow and your system has headroom (check Activity Monitor / `htop`), try increasing `--workers`. If you see high memory pressure or fan noise, reduce it.

When to use 1 worker

  • Short compositions (under 2 seconds / 60 frames) — parallelism overhead exceeds the benefit
  • Low-memory machines (4 GB or less)
  • Running renders alongside other heavy processes (video editing, large builds)

When to increase workers

  • Long compositions (30+ seconds) on a machine with 8+ cores and 16+ GB RAM
  • Dedicated render machines or CI runners
  • Docker mode on a well-provisioned host

Concurrent Renders

When multiple render requests hit the producer server simultaneously (common with AI agents), each render spawns its own set of Chrome worker processes. Too many concurrent renders can exhaust CPU and cause failures.

The producer server uses a request-level semaphore to queue renders. Only maxConcurrentRenders renders execute at a time — additional requests wait in a FIFO queue until a slot opens.

Configuration

# CLI flag
npx hyperframes render --max-concurrent-renders 2 --output output.mp4

# Environment variable (for the producer server)
PRODUCER_MAX_CONCURRENT_RENDERS=2

The default is 2 concurrent renders, which works well on 8-core machines where each render uses 2-3 workers.

Queue status

The producer server exposes a GET /render/queue endpoint that returns the current state:

{
  "maxConcurrentRenders": 2,
  "activeRenders": 1,
  "queuedRenders": 3
}

AI agents can poll this endpoint to decide whether to submit a render or wait.

SSE queue events

When using the streaming endpoint (POST /render/stream), queued requests receive a queued event before rendering begins:

{"type": "queued", "requestId": "...", "position": 2}

This lets agents report "waiting in queue" to users rather than appearing stuck.

Choosing a concurrency limit

Machine CPU cores Recommended limit
4-core VM 4 1
8-core workstation 8 2
16-core server 16 3-4
32-core render box 32 5-6
When in doubt, use 1. Renders will queue up and execute sequentially, but each one gets full CPU and finishes as fast as possible. This is better than 3 renders fighting for CPU and all finishing slowly — or failing.

Transparent Video

Hyperframes supports rendering with a transparent background — useful for overlays, lower thirds, subscribe cards, and any element you want to composite over other footage in a video editor.

Recommended format: MOV (ProRes 4444)

npx hyperframes render --format mov --output overlay.mov

MOV with ProRes 4444 is the industry standard for transparent video. It works in all major video editors:

  • CapCut
  • Final Cut Pro
  • Adobe Premiere Pro
  • DaVinci Resolve
  • After Effects
ProRes MOV files are large (typically 5-40 MB for short clips) because ProRes is a high-quality intermediate codec optimized for editing, not delivery. This is expected — the same tradeoff Remotion and professional pipelines make.

Format comparison

Format Codec Transparency Video editors Browsers File size
MOV ProRes 4444 Yes CapCut, Final Cut, Premiere, DaVinci, After Effects No Large
WebM VP9 Yes None (shows black background) Chrome, Firefox Small
PNG sequence RGBA PNGs (no encoding) Yes (lossless) After Effects, Nuke, Fusion (image-sequence import) No Largest
MP4 H.264 No All All Small
**WebM VP9 alpha** is technically supported but all major video editors ignore the alpha channel and render transparent areas as black. Only Chromium-based browsers (Chrome, Arc, Brave, Edge) decode VP9 alpha correctly. Safari does not support it. Use MOV for editor workflows and WebM only for browser-based playback.

PNG sequence (no encoding)

npx hyperframes render --format png-sequence --output frames/

--format png-sequence skips the encoder entirely. The captured RGBA frames are copied to <output>/frame_NNNNNN.png (zero-padded) and, if the composition has audio, an audio.aac sidecar is written alongside. Use this when you want lossless frames — for compositing in After Effects / Nuke / Fusion, or as the input to a custom encode pipeline. --output is treated as a directory and is created if it doesn't exist.

How it works

When you render with --format mov, --format webm, or --format png-sequence, Hyperframes:

  1. Captures each frame as a PNG with alpha channel (instead of JPEG for MP4)
  2. Sets Chrome's page background to transparent via Emulation.setDefaultBackgroundColorOverride
  3. Encodes with an alpha-capable codec (ProRes 4444 for MOV, VP9 for WebM); png-sequence skips encoding and writes the captured frames directly

Your composition's HTML should not set a background on html or body — leave it unset so the transparent background comes through.

Authoring transparent compositions

<style>
  /* Do NOT set background on html/body — leave them transparent */
  * { margin: 0; padding: 0; box-sizing: border-box; }

  [data-composition-id="my-overlay"] {
    position: relative;
    width: 1920px;
    height: 1080px;
    overflow: hidden;
    /* No background here either */
  }
</style>

Only the visible elements (cards, text, images) will appear in the final video. Everything else will be transparent.

Verifying transparency

  • In a browser: Open the MOV file — it won't play (ProRes is not a browser codec). Instead, render a WebM copy and open it in Chrome on a checkerboard background page.
  • In a video editor: Import the MOV file and place it on a track above other footage. Transparent areas should show the footage below.
  • Online tool: Use rotato.app/tools/transparent-video to verify your MOV or WebM has working transparency.

Tips

Use `draft` quality during development for fast previews. Switch to `standard` or `high` for final output.
  • Use npx hyperframes benchmark to find optimal settings for your system
  • Docker mode is slower but guarantees identical output across platforms
  • For compositions with many frames, --gpu can significantly speed up local encoding

Next Steps

Understand the determinism guarantees Render HDR10 MP4 from HDR video and image sources Full list of CLI commands and flags Fix common rendering issues