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Treasured's Movie Repair Guide -- Apple Lossless audio (ALAC)

Apple Lossless audio, or ALAC, is a modern audio encoding format. As its name indicates, it is lossless: encoding doesn't degrade quality.

ALAC can be found in audio files, usually in QuickTime and MP4 containers with the following extensions: .m4a .mp4a .mov
ALAC is rarely used to encode audio in video files.
iPhone application Voice Memos records .mp4a files containing ALAC audio.

Detection

Treasured can detect ALAC in damaged audio files, but it doesn't "preview" it.

How to repair a damaged ALAC file?

The easiest way is certainly to ask your Movie Repair Service to help you recover the unplayable audio file.

But for those who can program, here you have a few tips:

Pattern matching: Simple bitstream properties allow to accurately find ALAC frames.

A simple 60 bits pattern/mask checking 54 bits identifies the beginning of a frame:

00x0 0000 0000 0000 0000 0000 0000 0x00 0000 0xx0 0001 0011 000x x000 0000 xxxx
where x is a bit whose value can be 0 or 1

Then we create a QuickTime audio file by reindexing those ALAC frames.


Free Preview of corrupt ALAC recordings with:

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Version 3.4.1 • Sep '16 • 12 MB • Mac OS X