Detailed digital data analyses were conducted of the metadata contained in files produced on four iOS apps and then re-encoded with four (4) common audio/media editing programs, producing a total of twenty (20) separate M4A files. The purpose of this research was to identify changes made to the M4A file structure and metadata content by the re-encoding processes as they related to forensic audio authenticity examinations. The research found that the re-encoding processes produced clearly discernible differences, compared to the original M4A files. The M4A metadata format structure, the procedures followed, the changes identified in the metadata of the re-encoded files, and a discussion of the authenticity implications are listed.
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