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The licensing model

Media tooling licensing is where most projects get vague. ffmpeg-wasi keeps three licences deliberately distinct, so you always know exactly what you're holding.

Not legal advice

This explains the project's intent and structure. It is not legal advice; a formal licence review precedes any tagged release.

Three licences, kept apart

1. This repository's source — MIT

The build tooling (build/) and the engine (src/driver.c) are MIT. Two facts keep it that way:

  • It vendors no FFmpeg source. FFmpeg (and any GPL dependency such as x264) is cloned at build time, never committed here.
  • It links nothing. The tooling orchestrates a build — clone, configure, compile, package. It is not a derivative work of anything GPL, so it stays MIT, and it is yours to reuse.

That MIT pipeline — the reference "FFmpeg → WASI, libav-direct" build — is the valuable, reusable part we own.

2. The released artifacts — LGPL or GPL (your choice)

FFmpeg's libraries are LGPL-2.1-or-later by default. The artifact's licence is set entirely by what we enable:

Variant Built with Artifact licence
LGPL (default) stock libav*, no --enable-gpl, + openh264 (BSD) for H.264 encode LGPL-2.1-or-later
GPL (opt-in) --enable-gpl + libx264 GPL-2.0-or-later

openh264's BSD-2-Clause source is LGPL-compatible and needs no --enable-gpl, so it does not move the LGPL floor — but it does carry an AVC patent caveat, covered below.

LGPL is the floor. We cannot relicense libav* below it — it's the FFmpeg project's code, not ours. But LGPL is proprietary-compatible (you may use it in closed software, subject to its relink provision), which is what matters for adoption.

3. Your code that consumes the artifact — unaffected

afmpeg, or whatever loads the module, just downloads a .wasm. The LGPL/GPL obligation attaches to that artifact and whoever distributes it — never to the consuming source. afmpeg stays permissive throughout.

H.264 encode and the AVC patent pool

Both variants can encode H.264 — the LGPL variant via openh264 (BSD-2-Clause source), the GPL variant via libx264. Those are the copyright licences. The patent position is identical for both, and it is worth stating plainly.

Self-compiled openh264 is outside Cisco's patent grant

H.264/AVC is covered by a patent pool administered by Via LA (formerly MPEG LA). Cisco's well-known royalty-free grant for openh264 covers only the binary modules Cisco itself builds and distributes — it does not travel with the source. ffmpeg-wasi compiles openh264 from source, so our .wasm is not under Cisco's umbrella. The GPL variant's libx264 is no different: GPL is a copyright licence and never conveys patent rights.

We ship H.264 encode regardless, on a deliberate and bounded basis:

  • Volume. The AVC licence is royalty-free beneath the pool's annual unit threshold (the first 100,000 units/year). Our expected distribution sits well within it — and that headroom is the only reason shipping a self-compiled AVC encoder is tenable here.
  • Comply on demand. If Via LA or any AVC rights-holder asks us to stop distributing the encoder, we will pull it — promptly, from both variants — rather than contest it.
  • Sunset. The obligation is winding down. The last U.S. AVC essential patent in the pool (US 7,826,532) expires 2027-11-29; after that the standard is royalty-free in the U.S. and this caveat lapses. Other jurisdictions track a similar horizon.

This states the project's intent; it is not legal advice, and a formal review precedes any tagged release. For the authoritative, maintained patent roster see Via LA's AVC/H.264 patent list (the "Attachment 1" PDF, updated periodically) rather than any copy we could let go stale here.

HEVC & AV1 encode — the full native profile only

The heavy next-generation encoders ship only in the native driver's full profile (spec 0023); they are absent from every .wasm and from the lean/intermediate profiles. Their licence posture differs sharply from each other.

  • HEVC/H.265 via libx265 — GPL-2.0-or-later, so it enters the gpl variant only (behind --enable-gpl, exactly like libx264), never the LGPL default. And its patent exposure is harder than AVC's, not softer.

    HEVC patents are active and pooled — with no sunset

    H.265/HEVC is covered by multiple, fragmented patent pools (Via LA, Access Advance, plus unaffiliated holders) with no expiry on the horizon — unlike the AVC pool that sunsets 2027-11-29. We compile libx265 from source, so — as with x264 — GPL conveys no patent rights and our binary sits under no pool's grant. We mirror the AVC posture (self-compiled, low volume, comply-on-demand — we pull HEVC encode promptly from the gpl full driver if any HEVC rights-holder asks), but because the pools are active with no sunset, HEVC encode is the most patent-exposed thing we ship and is offered only on deliberate, bounded demand. Decode is unaffected (the native hevc decoder needs no pool licence to play HEVC).

  • AV1 via SVT-AV1 — BSD-3-Clause-Clear + the Alliance for Open Media patent grant. It is LGPL-clean, so it rides both variants of the full profile, and AV1 is royalty-free by design (AOMedia's patent commitment) — no patent caveat applies. This is the decisive advantage that makes AV1 the comfortable heavy codec to ship.

Why shipping both variants is clean

Every release publishes both ffmpeg-wasi-lgpl.wasm and ffmpeg-wasi-gpl.wasm, so you pick the licence that fits and never have to build. Distributing two separate, independent artifacts together is mere aggregation (GPLv3 §5): the GPL artifact does not "infect" the LGPL artifact, the MIT tooling, or your code. They simply coexist.

Obligations we meet

  • Per-asset labelling — each artifact states its licence; the provenance manifest records variant + licence.
  • Corresponding source — for every released binary, the source is the pinned upstream FFmpeg/x264/openh264 plus this public repository (our scripts + engine). Anyone can rebuild.
  • LGPL relink — because the build is public and the FFmpeg version pinned, a user can relink the LGPL artifact against a modified libav*.

In one sentence

MIT is what we own; LGPL is the floor for the artifact; GPL is opt-in for libx264; and your code stays yours.