OneTaskBy Tim King · Updated
AAC to MP3 Converter
Raw ADTS AAC to MP3, No Upload
OneTask is free, with no sign-up, and built by one person.
If this tool saved you time, a coffee helps keep new ones coming.
How the AAC To MP3 works
Drop in a .aac file from a radio stream recorder, dashcam, phone or video export and download it as an MP3. This AAC to MP3 converter decodes the stream with your browser's AAC decoder and encodes it at 128, 192 or 320 kbps without uploading anything.
AAC to MP3: from a successor codec back to MP3
AAC, Advanced Audio Coding, was designed as MP3's successor and is the audio codec of YouTube, Apple Music, DAB+ radio and most video files. A .aac file is the bare stream in ADTS framing, without the MP4 wrapper an .m4a uses. That raw form comes from stream rippers, some Android recorders and tools that extract audio from video. Many players and car stereos handle .m4a but choke on raw .aac, and MP3 is the safe common denominator.
What is lost in the transcode
- Two lossy generations. AAC already removed detail; MP3 removes more by its own rules. Pick an MP3 rate at least one step above the AAC rate.
- HE-AAC sources. Radio and low-bit-rate streams often use HE-AAC, which rebuilds treble from hints (spectral band replication). The decoder renders that treble and the MP3 encodes it, so a 48 kbps HE-AAC stream needs 128 kbps MP3 or more to keep it.
- No seeking index. Raw ADTS has no duration header, so the browser scans the whole file to measure it; very long recordings take a moment to load.
- No tags. Raw AAC carries almost no metadata, so the MP3 has none either.
Browser support for AAC decoding
Raw ADTS AAC decodes in Chrome, Edge, Safari on macOS and iOS, and Firefox on Windows and macOS. Firefox on Linux depends on the system FFmpeg libraries. HE-AAC v1 and v2 decode in all of these; the rarer AAC-LD and ELD variants used in some VoIP apps may not.
How to read the stats
Source shows channels, decoded rate, duration and file size. Output is the MP3 bit rate and Output size estimates the MP3. If the duration looks wrong, the AAC stream may be truncated or contain a corrupt frame.
AAC inside an MP4 container is handled by M4A to MP3, and M4A to WAV gives an uncompressed copy. Voice notes use Opus to MP3.
FAQ
What is the difference between AAC and M4A?
They usually hold the same AAC audio. An .aac file is the raw stream, while .m4a wraps it in an MPEG-4 container with a duration index, tags and artwork. Converting either to MP3 gives the same sound; the M4A version simply loads faster and carries metadata.
Which MP3 bit rate should I choose for AAC?
Go at least one step above the source. A 128 kbps AAC deserves 192 kbps MP3, and 256 kbps AAC deserves 320 kbps. Low-rate HE-AAC radio recordings sound best at 128 kbps or higher because the decoder rebuilds treble that MP3 must then encode.
Will AAC to MP3 lower the quality?
A little. Both codecs are lossy, so encoding the decoded AAC to MP3 adds a second round of loss. At 192 kbps or above the difference is hard to hear on most material; at 128 kbps it can show on bright, busy music.
Is my AAC file uploaded anywhere?
No. The file is decoded, processed and encoded inside your browser with the Web Audio API. Nothing is sent to a server, so it works offline once the page has loaded and your audio stays private.
See also: all Audio & Video tools, Units, Images, Documents, Data & Code.
Related tools
M4A To MP3
Convert iPhone and iTunes M4A audio to MP3 in your browser.
M4A To WAV
Turn iPhone voice memos and M4A files into editable WAV.
OPUS To MP3
Turn WhatsApp and Telegram .opus voice notes into MP3.
WAV To MP3
Encode WAV or other audio to MP3, without uploading it.
Audio To WAV
Convert MP3, M4A, FLAC or OGG to 16- or 24-bit WAV.