Access Unit

A Rust library for handling audio codec frames, with support for AAC and FLAC formats. The library provides utilities for frame detection, parsing, and manipulation, with a focus on broadcast and streaming applications.

Features

Automatic audio codec detection (AAC, FLAC, MP3) including MP4 container audio detection
AAC ADTS frame handling and validation
FLAC frame parsing and manipulation
MP3 frame header parsing and detection
Support for FMP4 container format
Access Unit abstraction for media streaming

Audio Codec Support

AAC Support

ADTS header parsing and validation
Frame extraction and manipulation
Support for common profiles (AAC-LC, HE-AAC v1/v2)
Sample rate detection and validation
Channel configuration handling

FLAC Support

Frame header parsing
Block size handling
Sample rate and channel configuration
Bits per sample validation
UTF-8 coded sample/frame numbers
CRC validation

MP3 Support

Frame header validation (sync, version, layer, bitrate, sample rate)
Frame length calculation
Frame detection within arbitrary byte streams

Usage

Detecting Audio Type

use audio_codec_handler::detect_audio;

let data: &[u8] = // your audio data
let audio_type = detect_audio(data);

match audio_type {
    AudioType::AAC => println!("AAC audio detected"),
    AudioType::FLAC => println!("FLAC audio detected"),
    AudioType::MP3 => println!("MP3 audio detected"),
    AudioType::Unknown => println!("Unknown audio format"),
    _ => println!("Other format")
}

Detecting MP4 Container Audio

use audio_codec_handler::mp4;

let data: &[u8] = // MP4 data

if mp4::is_mp4(data) {
    if let Some(audio_type) = mp4::detect_audio_track(data) {
        println!("Audio track codec: {:?}", audio_type);
    }
}

Working with AAC Frames

use audio_codec_handler::aac;

// Check if data is valid AAC
if aac::is_aac(data) {
    // Extract AAC frame data
    let aac_data = aac::extract_aac_data(&bytes_data);

    // Ensure proper ADTS header
    let processed_data = aac::ensure_adts_header(
        bytes_data,
        channels,
        sample_rate
    );
}

FLAC Frame Handling

use audio_codec_handler::flac;

// Parse FLAC frame header
let frame_info = flac::decode_frame_header(data)?;

// Split FLAC stream into frames
let frames = flac::split_flac_frames(data);

// Extract single FLAC frame
let frame = flac::extract_flac_frame(data);

// Create STREAMINFO metadata block
let streaminfo = flac::create_streaminfo(&frame_info);

MP3 Frame Detection

use audio_codec_handler::mp3;

if let Some((offset, header)) = mp3::find_frame(data) {
    println!("Found MP3 frame at offset {} with length {}", offset, header.frame_length);
}

Access Unit Handling

use audio_codec_handler::AccessUnit;

let unit = AccessUnit {
    key: true,
    pts: 0,
    dts: 0,
    data: data_bytes,
    avc: false,
    id: 1234
};

Frame Header Formats

AAC ADTS Header

|--- Sync Word (12 bits) ---|
|--- ID (1 bit) ---|
|--- Layer (2 bits) ---|
|--- Protection Absent (1 bit) ---|
|--- Profile (2 bits) ---|
|--- Sampling Frequency Index (4 bits) ---|
|--- Private Bit (1 bit) ---|
|--- Channel Configuration (3 bits) ---|
|--- Original/Copy (1 bit) ---|
|--- Home (1 bit) ---|

FLAC Frame Header

|--- Sync Code (15 bits) ---|
|--- Reserved (1 bit) ---|
|--- Block Size (4 bits) ---|
|--- Sample Rate (4 bits) ---|
|--- Channel Assignment (4 bits) ---|
|--- Sample Size (3 bits) ---|
|--- Reserved (1 bit) ---|

License

MIT

access-unit 0.1.2