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Audio format

AAC converter

An .aac file holds raw Advanced Audio Coding data, usually as an ADTS stream. AAC was designed as MP3's successor and delivers audibly better quality at the same bitrate, though the bare .aac extension is rarer than AAC audio traveling inside .m4a or .mp4 files.

Private for supported formats — processed in your browser

Convert supported files

Runs on your device

Drop AAC files here

Batch files can each use a different output. Nothing uploads for local conversions.

Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.

Where AAC comes from

AAC was standardized in 1997 as MPEG-2 Part 7, then extended under MPEG-4 with profiles like HE-AAC that bolt spectral band replication onto the core for low-bitrate work. Apple's 2003 decision to make it the iTunes Store format pushed AAC from broadcast niche to consumer default.

How AAC works

  • A pure MDCT transform codec, free of the hybrid filterbank compromise that limited MP3
  • AAC-LC dominates general use, while HE-AAC v1 and v2 stretch quality down to 32-64 kbps
  • The specification allows up to 48 channels and 96 kHz sampling
  • ADTS headers on every frame let raw streams be cut and resynchronized easily
  • Stereo transparency for most listeners arrives around 192 to 256 kbps with AAC-LC

When to use AAC

  • Receiving the audio track copied out of MP4 video without re-encoding
  • Streaming radio and HLS audio delivery
  • Encoding music for Apple and YouTube ecosystems
  • Low-bitrate speech feeds using HE-AAC

Strengths and limitations

Strengths

  • Noticeably more efficient than MP3 at equal bitrates
  • Hardware decoding in essentially every phone and TV
  • Scales from very low speech bitrates to multichannel surround
  • Extracting from MP4 or MOV video is a copy, not a transcode

Limitations

  • Raw ADTS files handle tags and cover art poorly
  • Encoder patent licensing still applies to vendors
  • Gapless playback information has no standardized home in a bare stream

Compatibility

AAC decoding is built into every browser, phone, and operating system, whether the audio arrives as a raw .aac stream or inside an .m4a wrapper. The last holdouts are elderly MP3-only car stereos and bargain portable players.

No standard tag container exists for raw ADTS streams; ID3 tags are sometimes prepended but poorly supported, so wrapping in .m4a is the reliable way to tag AAC.

Convert AAC to another format

Convert other formats to AAC