As a user, I want to validate M4A/AAC encoded audio as observational data

[jordanpadams]

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🧑‍🔬 User Persona(s)

Archive Manager

💪 Motivation

...so that I can confirm M4A/AAC encoded audio products are structurally valid and meet the standards expected by PDS4.

📖 Additional Details

M4A/AAC is one of only two valid values for Encoded_Audio/encoding_standard_id in PDS4 (the other being WAV, which is already fully validated via #662).

An interim fix was implemented in #1635 that recognizes M4A/AAC as a known encoding type and suppresses the false internal error, but actual content validation is not yet performed — instead a warning is emitted advising users to consult PDS4 experts.

This issue tracks implementing full content validation for M4A/AAC audio files, analogous to the WAV validation implemented in #662.

Acceptance Criteria

Given a properly labeled and valid M4A/AAC encoded audio product
When I perform validation of that data content
Then I expect validate to complete successfully with no errors or warnings about the audio content

Given a properly labeled but invalid M4A/AAC encoded audio product (e.g. file is not a valid M4A container)
When I perform validation of that data content
Then I expect validate to fail with an ERROR

⚙️ Engineering Details

• See interim fix: Throws an error processing M4A/AAC files #1635
• Reference implementation for WAV: As a user, I want to validate WAV encoded audio as observational data #662
• The AudioVideo.checkMetadata(true, false) call already exists in FileReferenceValidationRule for M4A/AAC but is currently bypassed pending this work — consult PDS4 experts to determine the appropriate validation checks for M4A/AAC container structure

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