Best audio formats for transcription

For transcription specifically, the format matters far less than the recording itself — a clean, close-mic'd voice in almost any format beats a noisy one in the "best" format. That said, the formats do differ in a few ways worth knowing.

Lossless vs lossy isn't really the question

WAV and FLAC are uncompressed or losslessly compressed — nothing is thrown away, so they give a transcription model the cleanest possible signal. In practice, this only shows up as a measurable difference at the edges: quiet speech, heavy background noise, or a recording that's been through several rounds of lossy re-compression already. MP3, AAC, and M4A at a normal bitrate (96kbps or higher) transcribe about as well as a lossless file for ordinary speech.

Where the format actually decides something

The format matters more for file size and compatibility than for transcription accuracy. A WAV recording of a long meeting can run into gigabytes; the same recording as MP3 or M4A is a fraction of the size and uploads faster. If you're recording something specifically to transcribe later, a compressed format at a reasonable bitrate is the practical choice — the accuracy cost is negligible, and the file is easier to move around.

OGG and WEBM are worth calling out specifically: OGG (Opus) is what WhatsApp voice messages actually are, and WEBM is what most browser-based recording tools produce by default. Neither is a format most people choose on purpose — they're just what shows up — and both transcribe fine.

The short version: don't convert a file just to change its format before transcribing it. Audio to Text accepts all of the formats above directly, and the recording quality itself will affect the result far more than which one you happen to have.