AAC to MP3 Converter
A file that ends in plain .aac is a bare audio stream, usually written by a recorder app, a call recorder or a capture tool rather than a music store. Converting it to MP3 gives it a proper file structure that every player can measure, seek and tag.
Audio Converter
or drop MP3, WAV, M4A … files here ·
Max 95 MB per file· Up to 20 files· Deleted after 30 minutes
Files are processed on our servers and deleted after 30 minutes.
Constant bitrate (CBR) gives a predictable size and works on every player. Variable bitrate (VBR) spends bits where the music needs them and is usually smaller at the same quality.
Keep the source rate unless a device asks for one. 44.1 kHz is CD standard, 48 kHz is video standard, 8 kHz is used by phone systems and AMR.
Mono halves the size of lossless files and is fine for voice recordings.
16-bit is CD quality. 24-bit keeps headroom for editing and mastering; converting a 16-bit source up does not add detail.
Optional. Seconds (e.g. 75) or minutes:seconds (1:15). Leave empty to start at the beginning.
Optional. Same format as the start time. Leave empty to keep everything up to the end.
How to use this tool
- 1
Upload the .aac files
Pick the recordings from your phone's storage or a computer folder. Up to 20 files per batch, 95 MB each.
- 2
Check the bitrate
This page uses 160 kbps, a comfortable match for most recorder output. Use 96 or 128 kbps with Mono for calls and dictation.
- 3
Convert to MP3
Press Convert to MP3. Each result shows its length, which should now match the real recording, and is ready to download.
If a recording plays but its length looks wrong, seeking jumps around, or a portal says the file type is unsupported, the culprit is often the raw .aac format, not the audio itself.
What a raw .aac file is
AAC, Advanced Audio Coding, was standardized by MPEG in 1997 as the successor to MP3 and is now the sound in most MP4 videos, iPhone recordings and streaming services. Most of the time it lives inside a container: an .m4a or .mp4 file with an index of where each part of the audio sits, the total duration, and tags such as title and artist.
A .aac file usually has none of that. It is AAC in ADTS form, the Audio Data Transport Stream from MPEG-2, where every short frame of audio carries its own small header so a decoder can start listening anywhere. That design suits radio broadcasting and live streams, where a listener tunes in mid-stream. Android's MediaRecorder offers it as an output format, which is why voice and call recorder apps produce .aac files, and capture tools write them because they can start saving instantly.
As a file to keep, ADTS is awkward. There is nowhere to store tags or cover art, duration has to be guessed, and some software only recognizes AAC inside M4A. Converting to MP3 solves all of these at once and keeps the file playable on hardware that predates AAC entirely.
- ADTS header at the start of every audio frame
- 7 bytes
- Header size when the frame carries a CRC checksum
- 9 bytes
- Audio samples per channel in each AAC-LC frame
- 1,024
- Year MPEG standardized AAC
- 1997
AAC to MP3 converter: problems it fixes
The player shows 2:10 for a ten-minute recording
The length was estimated from the start of a stream with no index. Convert to MP3 and the new file reports its real duration.
Dragging the progress bar jumps to the wrong place
Without an index, seeking is a guess. The converted MP3 seeks normally in phone players and editors.
The car stereo or an older player skips the file
Many head units read MP3 and WMA only, and some that play AAC still ignore raw .aac. MP3 at 160 kbps plays on all of them.
A form or transcription service says “unsupported format”
Upload checks often allow .mp3 and .m4a but not .aac. Convert here, and trim long silences with Start at and End at to save upload time.
A recorded call is too quiet to follow
Turn on Normalise volume to raise the overall level to −16 LUFS while converting.
AAC vs MP3: formats compared
AAC
Advanced Audio Coding
AAC is a lossy audio codec standardised by MPEG in 1997 as the successor to MP3. It delivers better quality than MP3 at the same bitrate and is the default audio in MP4 video, YouTube, Apple Music and most streaming services. Raw .aac files contain only the stream, while M4A and MP4 files wrap it in a container. Nearly every modern device plays AAC.
- Compression
- Lossy
- Transparency
- –
- Animation
- –
- Introduced
- 1997 · Moving Picture Experts Group (MPEG)
MP3
MP3 audio
MP3 (MPEG-1 Audio Layer III) is a lossy audio format developed largely at the Fraunhofer Institute and standardised by MPEG in 1993. It removes sounds the ear is unlikely to notice, shrinking music to about a tenth of CD size at 128–320 kbps. All patents have expired, and every phone, car stereo, browser and media player supports it. Quality loss is audible at low bitrates and accumulates with re-encoding.
- Compression
- Lossy
- Transparency
- –
- Animation
- –
- Introduced
- 1993 · Fraunhofer IIS / MPEG
Raw ADTS .aac streams from recorders and capture tools lack an index and tags, so many players misreport their length or cannot seek; MP3 turns them into ordinary, taggable files that every car stereo, editor and upload form accepts.
AAC to MP3: common questions
What is the difference between an .aac file and an .m4a file?
Both usually contain AAC audio. An .m4a wraps it in an MPEG-4 container with an index, tags and cover art; an .aac file is the raw stream in ADTS frames with none of that. Music stores and Apple apps use .m4a, while recorders and streaming tools often write .aac. For the container version, use M4A to MP3.
Why does my .aac recording show the wrong duration?
Raw ADTS has no index or total length, so a player has to estimate the duration from the first frames and the file size. Recordings with variable bitrate or silence at the start throw that estimate off. After conversion the MP3 carries its own length information, so players read it correctly.
Does AAC to MP3 lose quality?
A small amount, since one lossy format is decoded and re-encoded into another. Choose an MP3 bitrate at or above the source; for a 128 kbps recording, 160 kbps MP3 keeps it audibly the same. For editing rather than playback, convert to WAV with the audio converter instead.
Where do raw .aac files usually come from?
Android's built-in recording API can write AAC in ADTS form, so many voice recorder and call recorder apps save .aac. Dashcams, screen and stream capture tools, and internet radio recorders produce them too, and copying the audio track out of a video without re-encoding often gives a raw .aac.
Can I convert AAC audio that is inside a video?
Not on this page; it accepts audio files. Use MP4 to MP3 to pull the soundtrack out of a video and save it as MP3 in one step.
