mpeg4-audio-const

Definitions of types and constants for values defined by ISO/IEC 14496-3 (MPEG-4 Audio).

Overview

This crate provides newtype wrappers for the fields found in AudioSpecificConfig and ADTS headers:

• AudioObjectType - AAC profile - Main, LC, SSR, LTP, and others defined by the spec
• SamplingFrequencyIndex - Sampling rate index - 12 standard rates (96 kHz down to 8 kHz)
• ChannelConfiguration - Channel layout - mono through 7.1 surround and beyond

Usage

use mpeg4_audio_const::{AudioObjectType, ChannelConfiguration, SamplingFrequencyIndex};
use std::convert::TryFrom;

let profile  = AudioObjectType::try_from(2).unwrap();
assert_eq!(profile, AudioObjectType::AAC_LC);

let freq     = SamplingFrequencyIndex::new(0x3);  // 48 kHz
let channels = ChannelConfiguration::new(0x2); // stereo

assert_eq!(freq.freq(), Some(48000));
assert_eq!(channels, ChannelConfiguration::STEREO);

AudioObjectType implements TryFrom<u8>, rejecting the escape value (31) and values above 95. SamplingFrequencyIndex::new() is a const fn that rejects the escape value (0xf). SamplingFrequencyIndex::freq() returns the rate in Hz as Option<u32> (None for reserved indices). ChannelConfiguration::new() is a const fn that rejects values above 0xf.

Field widths by context

ADTS frame headers allow a limited subset of these header values; MP$/M4A allows for a wider field and can therefore accept a wider range of values