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AAC & ALACQuickTimeGarageBandDRM-free audiobooks
M4A, AAC, ALAC — what is actually in the file
M4A is a container, not a codec: inside is almost always AAC — what Apple devices record by default — or occasionally ALAC, Apple's lossless codec. Both decode natively here, and AAC preserves speech detail better than MP3 at the same bitrate, so an M4A is never the "worse" version of your audio. There is no reason to convert an M4A to MP3 or WAV before uploading — every conversion is either lossy or pointless, and the transcript will not improve.
The extension is the only thing most tools trip on. Windows media players and older editors sometimes refuse M4A files; the pipeline here decodes them with FFmpeg, so a file that will not play on your machine still transcribes fine.
Where M4A files come from
QuickTime screen and audio recordings, GarageBand and Logic bounces, the stock recorder on many Android phones, and DRM-free audiobooks all produce M4A or its sibling .m4b. Whatever made yours, upload it unchanged — and if it is specifically an iPhone voice memo, the voice-memo page covers getting it off the phone. After processing you get the same editor and TXT/SRT/VTT exports as every other format on the site.
Frequently asked questions
Is M4A worse than MP3 for transcription?
No — if anything, slightly better. M4A is normally AAC, which keeps more speech detail than MP3 at the same bitrate, and the model transcribes both equally well in practice. Accuracy is decided by the recording conditions, not by which of the two codecs wrapped it, so upload whatever your recorder produced.
Do I need to convert M4A to MP3 or WAV first?
No. M4A decodes natively here, so a conversion step adds nothing — and a lossy-to-lossy re-encode (M4A to MP3) can only degrade the audio. Converting makes sense only when some other tool in your workflow refuses the format; for transcription, drop it in as-is.
My M4A won't play on Windows — will it still transcribe?
Yes. Playback failures are almost always a missing codec or an app that doesn't recognize the container, not a broken file. Transcription here decodes with FFmpeg, which reads every M4A variant, so upload it even if your media player refuses it — if the file is genuinely unreadable you'll get a clear error, not a silent failure.
Are ALAC (Apple Lossless) files supported?
Yes — ALAC ships in the same .m4a container and decodes the same way. Keep in mind lossless audio buys no extra accuracy for speech, and ALAC files are several times larger than AAC, so if you're bumping into the upload size cap, an AAC export of the same recording transcribes identically.
Can I transcribe .m4b audiobooks?
DRM-free ones, yes: .m4b is the same container with a different extension, so rename the file to .m4a and upload it. Length matters more than format — 30 minutes anonymously, 1 hour with a free account, 10 hours on paid tiers — so long books go chapter by chapter. Audible .aax files are DRM-locked and cannot be decoded here.
What about .aac and .amr files from older phones and recorders?
Both are supported formats — raw .aac streams and the .amr files older phones and voice recorders produce upload directly. This page's file picker filters to .m4a, so for the adjacent extensions use the audio-to-text page, where the picker accepts every audio format.