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Sound sample descriptions

A sound sample description contains information that defines how to interpret sound media data.

Overview

The sound sample description contains information that defines how to interpret sound media data. This sample description is based on the standard sample description, as described in Sample description atom ('stsd').

The data format field contains the format of the audio data. This may specify a compression format or one of several uncompressed audio formats. The following table shows a list of some supported sound formats.

Format

4-character code

Description

Not specified

0x00000000

This format descriptor should not be used, but may be found in some files. Samples are assumed to be stored in either 'raw ' or 'twos' format, depending on the sample size field in the sound description.

kSoundNotCompressed

'NONE'

This format descriptor should not be used, but may be found in some files. Samples are assumed to be stored in either 'raw ' or 'twos' format, depending on the sample size field in the sound description.

k8BitOffsetBinaryFormat

'raw '

Samples are stored uncompressed, in offset-binary format (values range from 0 to 255; 128 is silence). These are stored as 8-bit offset binaries.

k16BitBigEndianFormat

'twos'

Samples are stored uncompressed, in two’s-complement format (sample values range from -128 to 127 for 8-bit audio, and -32768 to 32767 for 1-bit audio; 0 is always silence). These samples are stored in 16-bit big-endian format.

k16BitLittleEndianFormat

'sowt'

16-bit little-endian, twos-complement

kMACE3Compression

'MAC3 '

Samples have been compressed using MACE 3:1. (Obsolete.)

kMACE6Compression

'MAC6 '

Samples have been compressed using MACE 6:1. (Obsolete.)

kIMACompression

'ima4'

Samples have been compressed using IMA 4:1.

kFloat32Format

'fl32'

32-bit floating point

kFloat64Format

'fl64'

64-bit floating point

k24BitFormat

'in24'

24-bit integer

k32BitFormat

'in32'

32-bit integer

kULawCompression

'ulaw'

uLaw 2:1

kALawCompression

'alaw'

uLaw 2:1

kMicrosoftADPCMFormat

0x6D730002

Microsoft ADPCM-ACM code 2

kDVIIntelIMAFormat

0x6D730011

DVI/Intel IMAADPCM-ACM code 17

kDVAudioFormat

'dvca'

DV Audio

kQDesignCompression

'QDMC'

QDesign music

kQDesign2Compression

'QDM2'

QDesign music version 2

kQUALCOMMCompression

'Qclp'

QUALCOMM PureVoice

kMPEGLayer3Format

0x6D730055

MPEG-1 layer 3, CBR only (pre-QT4.1)

kFullMPEGLay3Format

'.mp3'

MPEG-1 layer 3, CBR & VBR (QT4.1 and later)

kMPEG4AudioFormat

'mp4a'

MPEG-4, Advanced Audio Coding (AAC)

kAC3AudioFormat

'ac-3'

Digital Audio Compression Standard (AC-3, Enhanced AC-3)

Topics

Using sample descriptions

See Also

Storing audio data