Audio speed changes — Input checklist

Worked example

Note the source length first: output length is source divided by speed, so 60 s at 0.8× becomes 75 s and 3 min at 1.25× becomes 2 min 24 s.

Listen to what the file actually contains. Single-voice speech with clear pauses usually holds up between about 0.75× and 1.5×, while music with drums or several people talking over each other starts to smear much sooner. The tool accepts MP3, WAV, M4A, AAC, FLAC, OGG, Opus and WebM audio, so a video file has to go through audio extraction first.

Picture a language teacher with a 60-second dictation recording who wants a slower copy for beginners. She finds the fastest sentence, plays only that part, and decides whether 0.8× is slow enough before processing the whole file.

A common mistake is starting from a copy that was already squeezed to 64 kbps or that was already sped up once. Every pass adds artifacts, so go back to the original recording, or a WAV or FLAC version of it, and apply the change a single time.

Before you run it, set the slider (0.25× to 4×, in steps of 0.05) and check the predicted length against the slot you need to fill. If 75 seconds will not fit the slide, the video or the lesson plan, change the multiplier now rather than exporting twice.

60 s at 0.8×

75 s theoretical duration

The multiplier changes duration only; the tool keeps pitch, so it cannot be used to make a voice sound lower or higher.