External tools & optional capabilities

ecmanim delegates a number of jobs to things outside the package — system programs, optional npm packages, network APIs, a WASM module, system fonts. The pattern is the same everywhere: probe lazily at the moment a feature needs the capability, fall back gracefully where a fallback exists. This page is the index of every instance. Run npx ecmanim checkhealth for an eager all-at-once report of what your machine has.

System programs (shelled out to; npm does not provide these)

tool	required?	used for	when missing
ffmpeg	for Node video	every Node render (PNG frames → MP4/WebM/GIF/MOV), partial-movie concat, audio muxing, watermark filters, silent TTS clips, PCM decode for getAudioData/FFT	no Node video output at all; browser rendering (canvas/WebM via MediaRecorder) is unaffected
ffprobe	with ffmpeg	duration/stream probing: video ingestion (VideoMobject), TTS clip timing	durations fall back to estimates or 0
say (macOS) / espeak-ng (Linux)	optional	the system voiceover TTS provider	provider reports unavailable; resolution falls through to silent (mute, correctly paced). See voiceover.md for install commands + better-sounding alternatives
latex (or pdflatex) + dvisvgm	optional	the publication-grade real-TeX math backend (MathTexDvisvgm)	falls back to MathJax — which is the default anyway
Chrome / Chromium (reached over CDP, not spawned)	optional	the opt-in GPU render path (renderGL) — drives WebGL in a headless Chrome at $MANIM_CDP_URL (default http://localhost:9222)	renderGL unavailable; the CPU renderer (including software 3D) is unaffected

Optional npm packages (optionalDependencies, lazy-imported)

package	used for	when missing
@napi-rs/canvas	all Node rasterization (render, renderStill, snapshots) + font registration	Node rendering unavailable (checkhealth flags it); pure-data features (plan IR, interchange, captions parsing…) still work
three	the browser WebGL backend (ecmanim/browser-three) and renderGL’s in-page renderer	WebGL backend unavailable; Canvas-2D browser backend and CPU 3D unaffected

(The regular dependencies — mathjax-full, opentype.js, gifenc, mp4-muxer, mp4box, polygon-clipping — are also lazy-imported for startup speed, but npm always installs them; they can only be “missing” under unusual bundler setups.)

Network services (opt-in via environment variables)

service	env var	used for	when unset
OpenAI TTS (api.openai.com)	OPENAI_API_KEY	the openai voiceover provider (gpt-4o-mini-tts)	provider reports unavailable; TTS resolution falls through (system → silent)
ElevenLabs TTS (api.elevenlabs.io)	ELEVENLABS_API_KEY	the elevenlabs voiceover provider	same fallthrough
—	MANIM_CDP_URL	override the Chrome DevTools endpoint for renderGL and the GPU e2e tests	defaults to http://localhost:9222; point it at an unreachable address to force-skip GPU paths

These are the only third-party services the library calls on its own. Separately, asset loaders accept http(s) URLs — remote video sources (VideoMobject / IIIF manifests), fonts, audio, Lottie files — but those only touch the network when you pass a URL instead of a local path. With local assets and no TTS keys, everything (including all built-in formats) runs fully offline.

Other outside-the-package capabilities

• WASM math core (packages/manim-wasm/manim_core.wasm): an opt-in accelerator loaded via loadWasm(); every accelerated function (bezierEvalWasm, earclipWasm, …) has a pure-JS implementation that is used when the module isn’t loaded. Also consumable from Python manim — see plugins.md.
• System fonts: discovered by walking the OS font directories and registered with the canvas at render time (checkhealth reports the count). With none found, text falls back to whatever the canvas default resolves to.

Bring-your-own backends (documented, not shipped)

Some features define a pluggable interface and document recommended external engines without bundling an adapter: planck.js / @dimforge/rapier2d for rigid-body physics (physics.md), ThorVG-WASM for full-fidelity Lottie import (interchange.md), ELK/dagre for large-graph diagram layout (animation-presentation.md), and Piper (or any TTS with word timings) via registerTTSProvider (voiceover.md).

Practical notes

• ffmpeg and @napi-rs/canvas are the two that matter for the core use case (Node video). Everything else is an enhancement with a fallback.
• Detection is lazy and per-feature. ecmanim probes at the moment a feature needs the capability (command -v, version calls, key presence, CDP probe, import() in try/catch) and picks the fallback silently where one exists. checkhealth is the eager version of those probes.

macOS notes

The project is developed primarily on Linux; two gaps show up on macOS.

• Vector-text glyph outlines (VText, MathTex, VectorDecimalNumber) need a concrete .ttf/.otf file for opentype.js to extract paths from — loadVectorFont() resolves one via fc-match sans-serif, then falls back to scanning common font directories (src/renderer/fonts-node.ts). On Linux, fc-match typically resolves straight to a .ttf (DejaVu Sans, Liberation Sans, …). On macOS, fc-match (from Homebrew’s fontconfig, if installed) commonly resolves sans-serif to a .ttc font collection (e.g. Hiragino), which is intentionally rejected — opentype.js doesn’t parse collections — and the old fallback scanner only checked Linux font directories, so resolution failed outright with “VText needs a font.” The scanner now also checks the standard macOS font directories (/System/Library/Fonts, /System/Library/Fonts/Supplemental, /Library/Fonts, ~/Library/Fonts) and finds Arial.ttf there. checkhealth’s font check was unaffected by this bug — @napi-rs/canvas discovers macOS system fonts fine for raster text; only the separate vector-outline path needed a real file path.
• The watermark filter (applyWatermark, drawtext) needs an ffmpeg build with libfreetype. Homebrew’s default ffmpeg formula does not compile that in (ffmpeg -filters | grep drawtext returns nothing); the separate ffmpeg-full formula does. This is an ffmpeg build limitation, not something ecmanim can detect-and-fall-back for beyond skipping — install ffmpeg-full (brew install ffmpeg-full) if you need text watermarks. Most Linux ffmpeg packages (including the standard apt/dnf builds) ship with libfreetype enabled by default, which is why this doesn’t surface there.