What is this AAC to M4A converter?
A free, browser-based tool that converts AAC audio to M4A. Add a file, preview it inline, and download the result. All processing happens locally in your browser, so your file is never uploaded and there is no watermark.
AAC to M4A rewraps the stream, it does not re-encode it
A raw .aac file is an ADTS stream: audio frames laid end to end, each with a tiny header, no global index, no stated duration. M4A takes those exact AAC frames and places them in an MP4 container, which adds a sample table describing where every frame sits. Nothing is decoded, no encoder runs, and the audio bytes stay identical; only the packaging changes.
That is why this conversion has none of the usual lossy trade-offs. There is no bitrate to pick and no generation loss to budget for. The waveform that comes out of a player is the same before and after.
Raw .aac recordings and the Apple ecosystem
Voice recorders, capture tools, and stream downloaders often hand you .aac files, and Apple software is where they hit friction: iTunes and the Music app may refuse the import, iPhones may play them but with a scrubber that jumps in coarse steps, and reported durations are often wrong because ADTS carries no length field, so players guess from the bitrate.
Inside M4A, the same audio gets exact duration, frame-accurate seeking, and a container with defined slots for tags, which ADTS lacks entirely. If a recorder keeps filling up with .aac files destined for an iPhone or a Mac library, rewrapping them is the correction, not a quality decision.
How to use it
- Add a AAC file on the left (drag & drop or click) — it shows an inline preview.
- Pick a quality preset (used only for lossy targets like MP3/M4A/OGG).
- Press “Convert & download” to get your M4A file. The first run downloads the ~30MB converter once.
Lossy vs lossless audio
WAV and FLAC are lossless — they preserve the original waveform exactly (FLAC is compressed, WAV is not). MP3, M4A (AAC) and OGG are lossy: they shrink the file by discarding inaudible detail, and the quality preset controls the bitrate. Converting a lossy file to a lossless format can't recover quality that was already lost. One special case: converting to M4A when the source is already AAC just repackages the container (a lossless remux) — instant and bit-exact.
