# Contributing to Concat

Thanks for being here. Concat is a video editor that runs entirely on the
user's machine, and it gets better mostly through people using it hard and
reporting what broke.

## The most valuable thing you can do

Grab a build from the [Releases](https://github.com/jub0t/Concat/releases) page
and edit a real video with it. Real footage finds what no reading of the
source does. A good bug report — what you did, what happened, your
OS, the media you used — is worth more than most patches.

Longer-form discussion lives in
[the contribution discussion](https://github.com/jub0t/Concat/discussions/3)
and on [Discord](https://discord.gg/DVuPfpXfqP).

## Before you write code

Open an issue or drop into Discord first for anything beyond a small fix. Large
areas of [`ROADMAP.MD`](ROADMAP.MD) are already in progress or intentionally
deferred, and it is genuinely no fun to review a big PR that has to be turned
down for reasons that were invisible from outside.

## Setting up

You will need Rust (see `rust-version` in `engine/Cargo.toml`), the FFmpeg
7+ development libraries (`brew install ffmpeg`; see `engine/README.md` for
Windows and Linux), cmake and a C++ compiler. Then:

```sh
cd engine && cargo run -p concat
```

That is the editor window. Everything - the engine, the host layer and the
Slint UI - is one Cargo workspace under `engine/`.

## Layout

| Path | What lives there |
|---|---|
| `engine/crates/` | The engine (core, media, render, export, project), the host layer (`concat-host`, `concat-speech`), the CLI, and `concat`, the Slint editor window |
| `test/` | Media and analysis fixtures |

[`ARCHITECTURE.md`](ARCHITECTURE.md) explains how these fit together and where
the sharp edges are. Read it before touching the engine.

## Checks

Run these before opening a PR:

```sh
cd engine && cargo fmt --check && cargo clippy --all-targets -- -D warnings && cargo test
```

If you added or changed text the interface shows, also run
`python3 scripts/locales.py` so the string inventory follows; CI checks it.
Translations live in one JSON file per language — see
[`TRANSLATING.md`](TRANSLATING.md).

New source files need a licence header — see below. Match the style of the code
around you; the engine avoids cleverness on purpose.

## Licensing your contribution

Concat is **AGPL-3.0-or-later** ([`LICENSE`](LICENSE)), with a plugin exception
so that Concat API plugins can carry their own licence
([`LICENSE-EXCEPTIONS.md`](LICENSE-EXCEPTIONS.md)).

Contributions are accepted under the CLA in [`CLA.md`](CLA.md). **You keep the
copyright in your work** — the CLA is a licence, not an assignment. It exists so
that copyright in Concat stays centralised, which is what makes the AGPL
enforceable against companies that take the code without honouring it.

Sign off your commits to indicate agreement:

```sh
git commit -s -m "your message"
```

Typo and documentation fixes do not need a sign-off.

### File headers

Every source file starts with:

```rust
// SPDX-License-Identifier: AGPL-3.0-or-later
// SPDX-FileCopyrightText: 2026 Jareer and Concat contributors
```

Keep your own copyright line if you want one — add it, don't replace what's
there.

### Third-party code

If your patch brings in code you did not write, say so in the PR: what it is,
where it came from, and its licence. Anything incompatible with
AGPL-3.0-or-later cannot be merged, and licence problems are much cheaper to
catch before a merge than after a release.

## Trademarks

The code is free to fork. The Concat name and logo are not covered by the AGPL
grant — see [`TRADEMARK.md`](TRADEMARK.md). Forks are welcome; please ship them
under your own name.

## Conduct

[`CODE_OF_CONDUCT.md`](CODE_OF_CONDUCT.md) applies to the repo, the Discussions
and Discord.