Rendering

bun /root/code/render-video-modal.ts \
  --entry-file src/index.ts \
  --composition <CompositionId> \
  --output output/video.mp4 \
  --props '{"key": "value"}'

The script automatically:

1. Bundles the Remotion project locally

2. Uploads the bundle to R2

3. Submits to Modal GPU for rendering

4. Polls until complete, then copies the result back

5. Reuse the existing project — don't re-scaffold The Remotion project lives at /root/code/src/ with node_modules already installed. For new videos, write new compositions there directly. Never run npm install or bun install unless dependencies are actually missing.

6. Edit in-place for style changes When a user asks for a color/style tweak (like gold instead of purple), only edit the composition .tsx file and re-render. Do not recreate the project or modify index.ts unless the composition ID or structure changes.

7. Use the GPU render command directly

bun /root/code/render-video-modal.ts
--entry-file src/index.ts
--composition <CompositionId>
--output output/video.mp4 Always offload to Modal GPU — never attempt local rendering first.

4. Output path discipline: Render directly to the session directory output path. Call yield_output with changeType: "new" on first render and changeType: "updated" on revisions — not "new" each time.

5. Confirm render complete before reporting done: Don't report the video as finished until the render script has exited successfully. Check the output file exists before calling yield_output.

6. Keep compositions short and self-contained: For simple animations (text, transitions), keep everything in one .tsx file. Avoid splitting into multiple components unless the user requests complexity.

Captions

When dealing with captions or subtitles, load the ./rules/subtitles.md file for more information.

Using FFmpeg

For some video operations, such as trimming videos or detecting silence, FFmpeg should be used. Load the ./rules/ffmpeg.md file for more information.

Audio visualization

When needing to visualize audio (spectrum bars, waveforms, bass-reactive effects), load the ./rules/audio-visualization.md file for more information.

Sound effects

When needing to use sound effects, load the ./rules/sound-effects.md file for more information.

How to use

Read individual rule files for detailed explanations and code examples:

• rules/3d.md - 3D content in Remotion using Three.js and React Three Fiber
• rules/animations.md - Fundamental animation skills for Remotion
• rules/assets.md - Importing images, videos, audio, and fonts into Remotion
• rules/audio.md - Using audio and sound in Remotion - importing, trimming, volume, speed, pitch
• rules/calculate-metadata.md - Dynamically set composition duration, dimensions, and props
• rules/can-decode.md - Check if a video can be decoded by the browser using Mediabunny
• rules/charts.md - Chart and data visualization patterns for Remotion (bar, pie, line, stock charts)
• rules/compositions.md - Defining compositions, stills, folders, default props and dynamic metadata
• rules/extract-frames.md - Extract frames from videos at specific timestamps using Mediabunny
• rules/fonts.md - Loading Google Fonts and local fonts in Remotion
• rules/get-audio-duration.md - Getting the duration of an audio file in seconds with Mediabunny
• rules/get-video-dimensions.md - Getting the width and height of a video file with Mediabunny
• rules/get-video-duration.md - Getting the duration of a video file in seconds with Mediabunny
• rules/gifs.md - Displaying GIFs synchronized with Remotion's timeline
• rules/images.md - Embedding images in Remotion using the Img component
• rules/light-leaks.md - Light leak overlay effects using @remotion/light-leaks
• rules/lottie.md - Embedding Lottie animations in Remotion
• rules/measuring-dom-nodes.md - Measuring DOM element dimensions in Remotion
• rules/measuring-text.md - Measuring text dimensions, fitting text to containers, and checking overflow
• rules/sequencing.md - Sequencing patterns for Remotion - delay, trim, limit duration of items
• rules/tailwind.md - Using TailwindCSS in Remotion
• rules/text-animations.md - Typography and text animation patterns for Remotion
• rules/timing.md - Interpolation curves in Remotion - linear, easing, spring animations
• rules/transitions.md - Scene transition patterns for Remotion
• rules/transparent-videos.md - Rendering out a video with transparency
• rules/trimming.md - Trimming patterns for Remotion - cut the beginning or end of animations
• rules/videos.md - Embedding videos in Remotion - trimming, volume, speed, looping, pitch
• rules/parameters.md - Make a video parametrizable by adding a Zod schema
• rules/maps.md - Add a map using Mapbox and animate it
• rules/voiceover.md - Adding AI-generated voiceover to Remotion compositions using ElevenLabs TTS