AAC MIME Type

About AAC audio files

A bare AAC stream in ADTS framing, as used by internet radio and HLS audio segments. For files people download and keep, the same audio in an M4A container is better, because it carries metadata and allows accurate seeking.

Other types seen for these files: audio/x-aac . Accept them when reading uploads, but send audio/aac yourself.

File signature

AAC files start with FF F1 or FF F9 (ADTS frame sync). The extension and the type a browser reports for an upload both come from the file name, so check these bytes on the server before trusting a file.

Serve .aac with the right Content-Type

Content-Type: audio/aac

audio/aac aac;

AddType audio/aac .aac

@aac path *.aac
header @aac Content-Type "audio/aac"

curl -sI https://example.com/file.aac | grep -i '^content-type'
# Content-Type: audio/aac

Set the type in code

res.set('Content-Type', 'audio/aac');
// Or make the browser download it:
res.attachment('file.aac');

import mimetypes

mimetypes.add_type('audio/aac', '.aac')  # if your system doesn't know it
mimetypes.guess_type('file.aac')[0]  # 'audio/aac'

mime.AddExtensionType(".aac", "audio/aac")
w.Header().Set("Content-Type", "audio/aac")

Accept .aac uploads

<input type="file" accept=".aac,audio/aac">

The accept attribute only filters the file picker; users can still choose another file. Listing the extension as well as the type matters, because operating systems don’t always report the type you expect.

Related types

• .m4a (audio/mp4): M4A audio
• .mp3 (audio/mpeg): MP3 audio
• .m3u8 (application/vnd.apple.mpegurl): HLS playlist

More audio

.wav , .ogg , .flac . Look up any extension or type with the MIME type lookup.

Sources

• IANA registration: audio/aac
• MDN: Common media types

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Frequently asked questions