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M4A content provenance

Content provenanceContent provenance: The record of where a piece of content came from and how it changed, carried with the content itself. for M4A files is a signed C2PA manifestC2PA manifest: The signed label itself: a small package inside a file that records who signed it, what they declared and how to check it. inside the file. Anyone can check who signed it and whether it changed, for free.

Start signing freeCheck a M4A file
A file holds a signed label in four layers: who signed it, what they declared including AI use, a fingerprint of the content, and a signature that seals them together.
The label sits inside the file. It names the signer, carries what they declared, fingerprints the content, and is sealed by a signature.
File
.m4a, MIME typeMIME type: The standard name for a file format, such as image/jpeg or audio/wav, that software uses to decide how to read a file. audio/mp4
Where the label sits
Inside the file, in its own box, one of the labelled parts the file is built from.
Standard
C2PAC2PA: The Coalition for Content Provenance and Authenticity: the group that publishes the open standard for content labels., the open standard for content labels.
Made for
Music stores, Podcast hosting, High-quality streaming

What Encypher supports for M4A

  • SignSupported

    Encypher signs M4A files under C2PA 2.2 and 2.4.

  • CheckSupported

    Free in the browser checker, with no account.

  • Formal conformanceSupported

    Covered by our C2PA 2.2 conformance record.

How to check a M4A file

  1. Open the free checker.

    It runs in your browser. No account needed.

    Open the checker

  2. Add your M4A file.

    Drop it in or pick it from your device.

  3. Read the result.

    It shows who signed and what they declared, such as AI use. It also shows if the file changed.

Where the label sits in a M4A file

The file is made of nested boxes, a layout called ISO BMFFBMFF: ISO Base Media File Format: the box structure behind MP4, MOV, HEIF and similar files.. The label gets a box of its own.

In an MP4, MOV, HEIC or AVIF file, the label sits in its own box beside the boxes that hold the picture and sound.
A M4A file keeps the label in its own box, one of the labelled parts the file is built from.

M4A is audio in an MP4 file, usually AAC sound. Apple Music, iTunes and many podcast hosts use it.

What keeps the label on a M4A file

You can add a hidden watermarkWatermark: A mark placed in the content itself, visible or hidden, so it can be found again after the file is copied. when you sign. If a copy loses its label, the watermark can lead back to the record.

Hard binding is a fingerprint of the exact file, so a re-encode breaks it. Soft binding is a watermark in the picture that still leads back to the label after a re-encode.
The fingerprint proves the file is unchanged. The watermark finds the label again when the file has changed or lost it.
  • Copying and moving the file keep the label.
  • Editing the sound after signing shows as a change.
  • Converting to another format writes a new file without the label, so sign the copy you publish.

For engineers

Show the technical detail
Embedding
JUMBF manifest store in a C2PA uuid box in the ISO BMFF structure
Accepted MIME types
audio/mp4, audio/x-m4a, audio/m4a
Signing versions
C2PA 2.2, 2.4
Verification
Any version. The checker reads any C2PA manifest it can parse, and the report names the version it checked against.
curl -X POST https://api.encypher.com/api/v1/sign/media \
  -H "Authorization: Bearer $ENCYPHER_API_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -F "file=@example.m4a" \
  -F "title=My M4A file" \
  -F "action=c2pa.created"

Support rows come from the live API capability matrix. Full reference: C2PA media types.

Keep reading

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