Apple files new patent: universal container for audio data
Posted by Dennis Sellers 
Jan 27, 2006 at 6:45am
On Jan. 26, the US Patent & Trademark Office revealed Apple’s patent titled “Universal container for audio data.” The original filing date is noted as July 2, 2004.
Apple’s abstract
Storing audio data encoded in any of a plurality of different audio encoding formats is enabled by parametrically defining the underlying format in which the audio data is encoded, in audio format and packet table chunks. A flag can be used to manage storage of the size of the audio data portion of the file, such that premature termination of an audio recording session does not result in an unreadable corrupted file. This capability can be enabled by initially setting the flag to a value that does not correspond to a valid audio data size and that indicates that the last chunk in the file contains the audio data. State information for the audio data, to effectively denote a version of the file, and a dependency indicator for dependent metadata, may be maintained, where the dependency indicator indicates the state of the audio data on which the metadata is dependent.
Apple’s background of the invention
Standard AIFF, AIFC and WAVE files, which consist of “chunks” of information, are limited to 4 gigabytes. High-resolution audio is now demanding that larger file sizes be possible. For example a 4 gigabyte file with 5.1 (i.e., 6 channels) at 96 KHz sample rate and 24 bits per sample has 41 minutes of play time, and a 4 gigabyte file with 5.1 at 192 KHz sample rate and 32 bit floating point per sample has 15 minutes of play time. With 8, 16, 32 or more channels, the play times become even shorter.
With AIFF and WAVE files, an audio application has two options when recording. The first option is to record the audio data and then update the audio data size field in the file at the end of the recording session. Applications rely on the size field to correctly parse the file. Thus, if an audio application were to terminate prematurely, or there was a power loss while recording, most applications would be unable to read the file because the size field would be incorrect. The second option is to update the size field repeatedly while audio data is written to the file. This process requires significant interactions with the hard disk on which the file is being stored, which significantly and negatively affects performance. Furthermore, if the recording application were to terminate in the midst of updating the size field, the file is also corrupt and unable to be read properly.
With the evolution and complexity of modern audio formats, a more generic and robust means needs to be developed to contain these formats. Based on the foregoing, there is a need for an audio file format that avoids the above-identified limitations of existing audio formats.
Apple’s universal containment overview
A universal and extensible container format for audio data (referred to as XAF: Extensible Audio Format) is described, which provides a mechanism for storing audio data encoded in any of a plurality of different audio encoding formats.
In one aspect of the invention, the underlying format in which the audio data is encoded is parametrically defined in an audio format chunk, encapsulating all the information for describing the basic format properties of a stream of audio data. Basic parameters define the properties of an audio stream sufficient to describe any constant bit rate audio format that has channels that are the same size. Additional parameters, defined in a packet table chunk, can be used to describe properties of an audio stream sufficient to describe any variable bit rate format. Based on the specified parameters, the audio data may be accessed and manipulated even when the actual encoding format is not known to the software performing such manipulation.
This may be the case, for example, when the audio data is encoded in a format that was developed after the software used to manipulate the audio data. Hence, the container is universal, and extensible, in that it can be used to store audio data in any encoded format, including those presently known as well as those not yet developed. Consequently, any parsers, readers, editors or players of XAF files do not require specific software code for each different audio encoding format that may be contained within an XAF file.
NOTICE
“Macsimum News” presents only a brief summary of patents with associated graphic(s) for journalistic news purposes as each such patent application and/or grant is revealed by the U.S. Patent & Trade Office. Readers are cautioned that the full text of any patent applications and/or grants should be read in its entirety for further details.
Today’s patent: “Universal container for audio data. Inventors: William G. Stewart, James E. McCartney, Douglas S. Wyatt.
Neo’s Notes
The following are only a sampling of the other topics covered in this audio patent:
Audio Data Block Size Overview, Dependency Tracking Overview, Overview of Audio Formats, Constant Bit Rate Formats, Variable Bit Rate Formats, Compressed Formats, Specific Types of XAF Chunks, General XAF File Layout, Format Description, Format Chunk Examples, Audio Data Chunk, Audio Data Size Parameter, Editing and Cross-Chunk Dependencies, Packet Table Chunk, Channel Descriptions Chunk, Optional Chunks, Hardware Overview, Extensions and Alternatives.
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Contributor
Dennis Sellers
Dennis has been a newspaper editor/reporter (seven years) and teacher (seven years). He has over 4,000 magazine, newspaper and online articles to his credit. He has also covered the Mac and tech industries for over a decade for such online publications as MacCentral, MacMinute and now MacsimumNews.
