baka-ac4 provides a standalone AC-4 decoder and command-line tools for MP4, M4A and raw AC-4 streams. The codec runs entirely in Rust, without a C decoder dependency.

• Reusable decoder — compressed packets in, planar f32 PCM out.
• Playback integration — embed the core in your existing audio pipeline.
• Practical CLI — decode to WAV, inspect stream metadata and benchmark decoding.

Install the CLI with Rust and Cargo:

cargo install baka-ac4-cli --version 0.1.0 --locked

# Decode to 16-bit PCM WAV
baka-ac4 decode input.mp4 output.wav

# Preserve float32 PCM output
baka-ac4 decode --f32 input.ac4 output.wav

# Inspect frame metadata and coding tools as JSON
baka-ac4 toc input.m4a

# Benchmark decoding over 10 rounds
baka-ac4 bench input.mp4 10

MP4/M4A files must contain an AC-4 track. The CLI also accepts raw .ac4 streams. Full QMF processing is enabled by default; the optional decode --fast shortcut changes the output and is not the fidelity-preserving path.

Add the decoder library to your project:

[dependencies]
baka-ac4-core = "0.1"

Reuse channel buffers across packets:

use baka_ac4_core::{Ac4Decoder, Result};

pub fn decode_packets(packets: &[Vec<u8>]) -> Result<()> {
    let mut decoder = Ac4Decoder::new()?;
    let mut pcm = Vec::new();

    for packet in packets {
        if let Some(frame) = decoder.decode_frame_into(packet, &mut pcm)? {
            // pcm[channel][sample]: planar f32 samples.
            // Consume PCM here before decoding the next packet.
            println!("{} Hz, {} channels", frame.sample_rate, pcm.len());
        }
    }
    Ok(())
}

Packets may include the 0xAC40 / 0xAC41 sync header. The decoder returns Ok(None) while waiting for an iframe. Frame metadata includes the sample rate, channel mask, sample count and key-frame flag. decode_frame() is also available when an owned Frame is more convenient.

Not every AC-4 profile or channel layout has been validated. The CLI writes basic WAV headers; applications that need speaker-position metadata should use the core's channel mask.

Use baka-ac4-core as the codec layer and keep source access, demuxing, timestamps and audio output in your player. Prefer the system decoder when it supports the stream; use Rust decoding when it does not.

AC-4 decoding is stateful. Seek from a suitable iframe and discard pre-roll before the target. Recreate the decoder when complete history isolation is required: flush() marks the stream for resynchronization but does not clear every history array.

The core does not provide networking, DRM decryption or a playback device. The CLI reads the input file into memory and is intended for file conversion and inspection, not as a streaming playback layer.

cargo build --release --locked
cargo test --release --locked
cargo clippy --release --all-targets --locked -- -D warnings

Use release builds for decoding performance and mobile integration. Robustness tests include embedded fixtures; additional reference and stream-inspection tools are in tools/.

GPL-3.0-or-later. Third-party attribution is retained in NOTICE.