AAC is the lossy codec behind most streaming audio. These files carry it as a bare ADTS stream, with no MP4 container around the frames: the shape broadcast feeds and HLS audio arrive in. That makes aac/adts-30s.aac a good test of whether a decoder can find frame boundaries on its own, or quietly expects the box structure of an M4A file.

aac/adts-30s.aac is a 440 Hz sine wave, thirty seconds long, 48 kHz stereo, at 130.6 kbps counting each frame's ADTS header. A pure tone is easy to check by ear and by spectrum: any pitch shift, dropout or channel problem is obvious.

Use it to test upload validation that inspects a file's first bytes, players that must stream rather than seek, and transcoders that need to wrap raw AAC in a container. For the same audio inside MP4, see M4A; for the transport stream that often carries ADTS audio, see TS.

Every AAC file in one command, each checked against its hash: npx loremfile get --format aac, or loremfile get --format aac after pip install loremfile.

Sample AAC audio files for testing, free, CC0 and hotlinkable

Related formats