A file can be selected in the upload box and still fail before speech recognition. We created original videos containing the same synthetic English sentence, one with AAC audio and another with AC three audio. We also kept a deliberately incomplete copy of the AAC video. In this browser, the complete AAC video produced the control sentence. The AC three video and incomplete copy both returned the same audio decoding warning.

Local file inspection identified the audio codecs in the complete videos. The deliberately incomplete copy failed inspection because container metadata was missing. Those are different source conditions, yet the tool displayed the same decoding message. Its code maps more than one decoder error to that message. The test does not establish support across all browsers, and a warning alone cannot identify the exact cause in another file.

Use a recording you can actually open, and save a fresh, complete WAV audio export before retrying. Do not expect renaming a broken file to rebuild missing data. Select the saved audio in the upload box, choose the spoken language, and generate the transcript. Our complete WAV control returned the reference sentence after the failed video attempt. Review your own result against the playable source. The field note includes actual files and outcomes, original diagrams, and synthetic narration.