OpenJOC

OpenJOC is an independent, clean-room E-AC-3 JOC decoder and spatial renderer written in Rust. It decodes supported E-AC-3/JOC input, reconstructs carrier-local object signals, and renders speaker or binaural output through one platform-neutral engine.

Download the latest release. OpenJOC is not affiliated with, endorsed by, or sponsored by Dolby Laboratories.

Documentation

Read the OpenJOC documentation site · 阅读简体中文文档

What it supports

• E-AC-3 JOC decoding with bounded reconstruction;
• supported speaker presets from 2.0 through 22.2 and custom geometry up to 64 output channels;
• two-channel virtual-speaker binaural rendering with the bundled SADIE II D1 HRTF or a supported local SOFA file;
• reconstructed ADM BWF interoperability output with decoded JOC/OAMD binding within a documented profile;
• Rust and versioned C ABI embedding surfaces;
• project-provided FFmpeg, GStreamer, mpv, and Windows DirectShow/LAV integrations.

Read the capability matrix for the evidence boundary behind each claim.

Quick start

Build or download OpenJOC, then render a JOC programme:

openjoc render-joc input.m4a --layout 7.1.4 --output output.wav
openjoc render-joc input.m4a --binaural --output headphones.wav
openjoc export-adm input.m4a --output reconstructed.wav
openjoc validate-adm reconstructed.wav

Use openjoc inspect input.ec3 to inspect a carrier before rendering. The quick-start guide covers the first render and points to the detailed output contracts.

For custom geometry, use --layout-file LAYOUT.json; the documented limit is 64 output channels.

Windows playback

The optional Windows package provides an isolated OpenJOC-enabled LAV Audio Decoder. It installs beside stock LAV and does not change PotPlayer automatically:

1. Extract the package from the OpenJOC releases page.
2. Run install.bat, then require verify.bat to report PASS.
3. In PotPlayer, add LAV Audio Decoder (OpenJOC) in Filter Control → Filter Priority (Overall) and set it to Prefer.

The Windows LAV / PotPlayer guide documents the seven fixed PCM policies, passthrough behavior, rollback, and hardware boundary.

Important boundaries

Reconstructed ADM is an interoperability-oriented representation of the decoded JOC object scene. It is not recovery of the original authored Atmos master. OpenJOC does not recover original authoring identity, source-stem PCM, unquantized automation, Dolby authoring provenance, or a lossless JOC-to-ADM round trip.

The decoded Objects vs authored Objects page explains the identity boundary. The renderer-equivalence limitation explains why a generic ADM renderer is not guaranteed to localize exactly like native JOC playback.

API and integrations

• Rust API — serial OpenJocSession lifecycle and owned interleaved f32 output.
• C ABI — opaque handles, bounded stream decoding, custom geometry, and panic containment.
• Integration overview — current FFmpeg, GStreamer, mpv, player-bundle, and Windows contracts.

Build from source

Use the Rust toolchain declared in Cargo.toml:

cargo build -p openjoc-cli --release --locked
./target/release/openjoc --version

Contributors should follow CONTRIBUTING.md and run the workspace quality gates before committing.

Help wanted

OpenJOC is usable today, but several research and validation problems remain open. Contributions are especially welcome around native-renderer equivalence, reconstructed-PCM headroom, and physical multichannel hardware validation.

See Open Problems & Contribution Opportunities before starting work on codec or renderer semantics. For difficult research, starting a Discussion first is recommended so work does not repeat an already investigated path.

License and notices

OpenJOC core code is licensed under Apache-2.0. Integration bundles may include components under additional terms; see THIRD_PARTY_NOTICES.md and package-specific notices. Dolby, Dolby Atmos, SADIE, FFmpeg, GStreamer, mpv, LAV Filters, PotPlayer, Windows, and related names are marks of their respective owners.