Apple Lossless Audio Codec is now open source (Apache license) Options

[adamgibbo]

The Apple Lossless Audio Codec (ALAC) is an audio codec developed by Apple and supported on iPhone, iPad, most iPods, Mac and iTunes. ALAC is a data compression method which reduces the size of audio files with no loss of information. A decoded ALAC stream is bit-for-bit identical to the original uncompressed audio file.



The Apple Lossless Audio Codec project contains the sources for the ALAC encoder and decoder. Also included is an example command line utility, called alacconvert, to read and write audio data to/from Core Audio Format (CAF) and WAVE files. A description of a 'magic cookie' for use with files based on the ISO base media file format (e.g. MP4 and M4A) is included as well.



The Apple Lossless Audio Codec sources are available under the Apache license. Details can be found here http://www.apache.org/licenses/LICENSE-2.0.

http://alac.macosforge.org/

[googlebot]

The Apple Lossless Format
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4
5 Apple Lossless supports the following features. Not all of these are implemented in alacconvert, though they are in the codec code provided.
6
7 1. Bit depths 16, 20, 24 and 32 bits.
8 2. Any arbitrary integer sample rate from 1 to 384,000 Hz. In theory rates up to 4,294,967,295 (2^32 - 1) Hz could be supported.
9 3. From one to eight channels are supported. Channel orders for the supported formats are described as:
10 Num Chan Order
11 1 mono
12 2 stereo (Left, Right)
13 3 MPEG 3.0 B (Center, Left, Right)
14 4 MPEG 4.0 B (Center, Left, Right, Center Surround)
15 5 MPEG 5.0 D (Center, Left, Right, Left Surround, Right Surround)
16 6 MPEG 5.1 D (Center, Left, Right, Left Surround, Right Surround, Low Frequency Effects)
17 7 Apple AAC 6.1 (Center, Left, Right, Left Surround, Right Surround, Center Surround, Low Frequency Effects)
18 8 MPEG 7.1 B (Center, Left Center, Right Center, Left, Right, Left Surround, Right Surround, Low Frequency Effects)
19 4. Packet size defaults to 4096 sample frames of audio per packet. Other packet sizes are certainly possible. However, non-default packet sizes are not guaranteed to work properly on all hardware devices that support Apple Lossless. Packets above 16,384 sample frames are not supported.

Within the audio domain, there are many possible subdomains. For example: low bitrate speech, high-bitrate multi-channel music, etc. FLAC itself does not target a specific subdomain but many of the default parameters of the reference encoder are tuned to CD-quality music data (i.e. 44.1kHz, 2 channel, 16 bits per sample). The effect of the encoding parameters on different kinds of audio data will be examined later. (Official FLAC FAQ)

Which one looks better?

The FLAC and Ogg FLAC formats themselves, and their specifications, are fully open to the public to be used for any purpose (the FLAC project reserves the right to set the FLAC specification and certify compliance).

FLAC is no industry standard. There is no committee, where interested parties could participate according to an open, defined protocol. It's just a bunch of guys who created a (good) format, gave it into the public domain, and now reserve the right to certify and shape the future of the standard.

Why should Apple accept the sovereignty of outside community developers to decide whether Apple products are FLAC compliant or not? Why should they let them decide how and when they want to support multichannel and additional bitrates and whether this breaks existing Apple compatibility. What about Apple users trying to use embedded cue-sheets with meta data, there is no unambiguous definition available.

Apple wants this to just work, without users having to think about the details. And I don't see them doing a bad job concerning ALAC.

This post has been edited by googlebot: Oct 28 2011, 20:09