aac

Documentation

Overview

Package aac - parse and generate AAC meta data including ADTS headers.

Index

• Constants
• Variables
• type ADTSHeader
  • func DecodeADTSHeader(r io.Reader) (header *ADTSHeader, offset int, err error)
  • func NewADTSHeader(samplingFrequency int, channelConfig byte, objectType byte, plLen uint16) (*ADTSHeader, error)
  • func (a ADTSHeader) Encode() []byte
  • func (a ADTSHeader) Frequency() uint16
• type AudioSpecificConfig
  • func DecodeAudioSpecificConfig(r io.Reader) (*AudioSpecificConfig, error)
  • func (a *AudioSpecificConfig) Encode(w io.Writer) error

Constants

const (
	// AAClc - AAC-LC Low Complexity
	AAClc = 2
	// HEAACv1 - HE-AAC version 1 with SBR
	HEAACv1 = 5
	// HEAACv2 - HE-AAC version 2 with SBR and PS
	HEAACv2 = 29
)

Variables

var FrequencyTable = map[byte]int{
	0:  96000,
	1:  88200,
	2:  64000,
	3:  48000,
	4:  44100,
	5:  32000,
	6:  24000,
	7:  22050,
	8:  16000,
	9:  12000,
	10: 11025,
	11: 8000,
	12: 7350,
}

FrequencyTable maps frequency index to sample rate in Hz

var ReverseFrequencies = map[int]byte{
	96000: 0,
	88200: 1,
	64000: 2,
	48000: 3,
	44100: 4,
	32000: 5,
	24000: 6,
	22050: 7,
	16000: 8,
	12000: 9,
	11025: 10,
	8000:  11,
	7350:  12,
}

ReverseFrequencies converts sample frequency to index

Types

type ADTSHeader

type ADTSHeader struct {
	ID                     byte // 0 is MPEG-4, 1 is MPEG-2
	ObjectType             byte
	SamplingFrequencyIndex byte
	ChannelConfig          byte
	HeaderLength           byte // Should be 7 or 9
	PayloadLength          uint16
	BufferFullness         uint16
}

ADTSHeader - data for an unencrypted ADTS Header with one AAC frame. Not used in mp4 files, but in MPEG-2 TS. Defined in ISO/IEC 13818-7

func DecodeADTSHeader

func DecodeADTSHeader(r io.Reader) (header *ADTSHeader, offset int, err error)

DecodeADTSHeader by first looking for sync word

func NewADTSHeader

func NewADTSHeader(samplingFrequency int, channelConfig byte, objectType byte, plLen uint16) (*ADTSHeader, error)

NewADTSHeader - create a new ADTS header

func (ADTSHeader) Encode

func (a ADTSHeader) Encode() []byte

Encode - encode ADTSHeader into byte slice

func (ADTSHeader) Frequency

func (a ADTSHeader) Frequency() uint16

Frequency looks up the sampling frequency for index in ADTSHeader

type AudioSpecificConfig

type AudioSpecificConfig struct {
	ObjectType           byte
	ChannelConfiguration byte // Defined in Table 1.19
	SamplingFrequency    int
	ExtensionFrequency   int
	SBRPresentFlag       bool
	PSPresentFlag        bool
}

AudioSpecificConfig according to ISO/IEC 14496-3 Syntax specified in Table 1.15

func DecodeAudioSpecificConfig

func DecodeAudioSpecificConfig(r io.Reader) (*AudioSpecificConfig, error)

DecodeAudioSpecificConfig -

func (*AudioSpecificConfig) Encode

func (a *AudioSpecificConfig) Encode(w io.Writer) error

Encode - write AudioSpecificConfig to w for AAC-LC and HE-AAC