Detailed digital data analyses were conducted of the metadata contained in a lossy and a lossless file produced on the iPhone Voice Memos app in iOS 12.1.2. The lossy file was re-encoded with four (4) common audio/media editing programs, producing a total of five (5) separate M4A files. The lossless file was exported to a new lossless file using one (1) of the editing programs, and converted to a new lossless file with iTunes, using an intermediate PCM WAV file. The purpose of this research was to identify changes made to the basic M4A file structure and metadata content by the re-encoding processes as they relate 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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