M4A Audio
| Format | M4A Audio |
|---|---|
| Short name | M4A |
| Category | media |
| Platforms | macOS, iOS |
| Crush support | Supported (MediaParser) |
| Status | Reviewed |
| Last reviewed | 2026-10-04 |
Forensic relevance
ISOBMFF audio-only container (ftyp brand 'M4A ') typically containing AAC (lossy) or ALAC (lossless) audio. Used for iTunes/Apple Music purchases and downloads, iOS Voice Memos, and GarageBand exports. Shares box structure with MP4 — same mvhd timestamps (QuickTime epoch, seconds since 1904-01-01 UTC). iOS Voice Memos store recordings as M4A with the writing application field set to 'com.apple.VoiceMemos' — absence or alteration of this field is a forgery indicator. The 'ilst' box contains iTunes-style metadata tags (title, artist, album, comment, encoded date). iTunes Store purchases with FairPlay DRM use .m4p extension and cannot be decoded without authorization. ALAC variant (Apple Music lossless) is bit-perfect — no lossy artefacts.
Signatures
| Offset | Hex | ASCII (non-printable as .) | Description |
|---|---|---|---|
| offset 4 (0x4) | 66 74 79 70 4D 34 41 20 | ftypM4A | ftyp box with Apple audio major brand 'M4A ' |
| offset 4 (0x4) | 66 74 79 70 4D 34 42 20 | ftypM4B | ftyp box with Apple audiobook major brand 'M4B ' |
| offset 4 (0x4) | 66 74 79 70 4D 34 50 20 | ftypM4P | ftyp box with Apple protected audio major brand 'M4P ' |
Known extensions
.m4a, .m4p, .m4b
References
- MPEG-4 Part 14 — MP4/M4A file format (Wikipedia) https://en.wikipedia.org/wiki/MP4_file_format
- Forensic originality identification of iPhone's voice memos (J. Phys.: Conf. Ser. 2019) https://doi.org/10.1088/1742-6596/1345/5/052053
- ExifTool QuickTime tags (M4A metadata fields) https://exiftool.org/TagNames/QuickTime.html
Cite this entry
Crush Format Reference, “M4A Audio”. https://kalink0.github.io/crush-forensics/formats/m4a/ — source: crush/data/build_formats_db.py at commit 640a2a9928f4e36a976b89901512a8dce824d093, built 2026-10-21 06:46:19 UTC.
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