# 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`](/documentation/quicktime-file-format/Sample_description_atom). 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 [`Sound sample description version 0`](/documentation/quicktime-file-format/Sound_sample_description_version_0) A sound sample description that supports only uncompressed audio in raw or twos-complement format. [`Sound sample description version 1`](/documentation/quicktime-file-format/Sound_sample_description_version_1) An extended sound sample description that supports compressed audio, and includes the ability to add atoms to the sound description. [`Sound sample description version 2`](/documentation/quicktime-file-format/Sound_sample_description_version_2) An updated sound sample description that adds high resolution audio. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)