Difference between Apple lossless encoding options

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Dcislander
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Difference between Apple lossless encoding options

Post by Dcislander » Fri May 04, 2007 1:52 pm

OK, so I did my forum search and I know to use MPEG4 Audio for Apple Lossless, but out of pure curiosity, what is Apple CAF File (Apple Lossless) and what is the diff between the CAF and the MP4?

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sbooth
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Post by sbooth » Fri May 04, 2007 8:04 pm

CAF is Apple's Core Audio Format. See http://developer.apple.com/documentatio ... ion_1.html for full info, but in brief (from the link):
Apple’s Core Audio Format is a flexible, state-of-the-art file format for storing and manipulating digital audio data. It is fully supported by Core Audio APIs on Mac OS X v10.4 and later and on Mac OS X v10.3 with QuickTime 7 or later. CAF provides high performance and flexibility, and is scalable to future ultra-high resolution audio recording, editing, and playback.

CAF files have several advantages over other standard audio file formats:

Unrestricted file size
Whereas AIFF, AIFF-C, and WAV files are limited in size to 4 gigabytes, which might represent as little as 15 minutes of audio, CAF files use 64-bit file offsets, eliminating practical limits. A standard CAF file can hold audio data with a playback duration of hundreds of years.

Safe and efficient recording
Applications writing AIFF and WAV files must either update the data header’s size field at the end of recording—which can result in an unusable file if recording is interrupted before the header is finalized—or they must update the size field after recording each packet of data, which is inefficient. With CAF files, in contrast, an application can append new audio data to the end of the file in a manner that allows it to determine the amount of data even if the size field in the header has not been finalized.

Support for many data formats
CAF files serve as wrappers for a wide variety of audio data formats. The flexibility of the CAF file structure and the many types of metadata that can be recorded enable CAF files to be used with practically any type of audio data. Furthermore, CAF files can store any number of audio channels.

Support for many types of auxiliary data
In addition to audio data, CAF files can store text annotations, markers, channel layouts, and many other types of information that can help in the interpretation, analysis, or editing of the audio.

Support for data dependencies
Certain metadata in CAF files is linked to the audio data by an edit count value. You can use this value to determine when metadata has a dependency on the audio data and, furthermore, when the audio data has changed since the metadata was written.

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