Best Audio File Formats for Speech-to-Text Accuracy

File format alone will not save a bad recording, but it can quietly cost you accuracy on a good one. Here is how to think about formats when you upload audio for speech-to-text.

Lossless formats give the model the most signal

WAV and FLAC keep the original audio intact. If you have the option, upload one of these for interviews, research sessions, and any recording where wording really matters.

Lossless files are larger, but transcription is a one-time cost per recording. The accuracy benefit usually outweighs the upload time.

Compressed formats are fine when they are clean

MP3, M4A, and AAC are widely used for a reason: they sound great at sensible bitrates. For podcasts and meetings, a 128 kbps or higher compressed file is usually indistinguishable from lossless to a transcription model.

Avoid stacking compression. Re-encoding an already compressed file from one MP3 to another can introduce artifacts that hurt transcription quality, especially for quiet speakers.

Video uploads work, but the audio still has to be clean

Uploading MP4 or MOV video is convenient because you skip the export step. The model only listens to the audio track, so the same recording quality rules apply.

STT AI accepts both audio and video uploads, so you can pick whichever format keeps your workflow simple without giving up accuracy.