Fit Audio to an Exact Length
Pick a clip and a target length — it's padded with silence or trimmed to hit that exact duration, in your browser, nothing is uploaded.
Make an audio clip an exact number of seconds
Upload a clip and set a target length. If the clip is shorter than the target it is padded with silence to reach exactly that duration; if it is longer it is trimmed to exactly that duration. Both cases come from one ffmpeg pass: apad=whole_dur=T extends the stream to the target length, and -t T guarantees the output is exactly T seconds. It's the tool you want when a spot has to fill a fixed slot — a 15- or 30-second ad break, a looping bumper, a fixed-length intro — no matter how long the source happens to be.
Worked example
You have voiceover.mp3 that runs 24.6 seconds and it needs to fill a 30-second radio slot. Upload it, set Target length to 30, leave Pad silence at on End, and choose mp3. The exported voiceover-fit.mp3 is exactly 30.000 seconds: your voice plays from the start and 5.4 seconds of clean silence follows. Switch Pad silence at to Start instead and the silence lands before the voice, so the audio ends precisely on the 30-second mark — handy when the important beat has to hit the end of the slot.
Padding vs. trimming
Pad silence at only decides where silence is added when the clip is shorter than the target. When the clip is longer than the target it is always trimmed from the end, whichever pad position you pick — so a 40-second clip fit to 30 returns its first 30 seconds either way. To cut a specific in/out selection rather than fit-to-length, use trim-audio; to repeat a short sound until it fills a length, use audio-loop.
Limits and edge cases
- Input and output are capped at 10 MiB (the file stays in your browser).
- Target length must be greater than
0and at most3600seconds (1 hour). - The audio is re-encoded (not stream-copied) so appended silence joins the decoded audio cleanly with no click at the seam. Embedded album art is dropped.
- Output formats: mp3 (192 kbps, default), wav, ogg, flac, or m4a.
FAQ
What happens if my clip is already longer than the target?
It is trimmed to exactly the target length, cutting from the end. For example, a 45-second clip fit to 30 returns its first 30 seconds. The Pad silence at setting has no effect in this case — it only controls where silence goes when the clip is shorter than the target.
Can I add the silence before the clip instead of after it?
Yes. Set Pad silence at to Start and the silence is prepended, so the clip ends exactly on the target mark. Leave it on End (the default) to append silence after the clip so it starts at zero. Padding at both ends or in the middle isn't supported here.
Is the output exactly the length I ask for?
Yes — the output is trimmed to precisely the target with -t, so a request for 30 produces a 30.000-second file. The one practical ceiling is the 10 MiB output cap, so very long targets in a lossless format (wav/flac) may exceed the limit before they reach an hour.
Is my audio uploaded anywhere?
No. The page runs ffmpeg WebAssembly in your browser tab, so your audio never leaves your device. The CLI and chat versions run the same ffmpeg plan through the local tool runtime.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool audio-fit-to-length 'url=https://example.com/input' 'duration=30' 'pad=end' 'format=mp3'New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/audio-fit-to-length/?url=https://example.com/input&duration=30&pad=end&format=mp3Machine-readable descriptor: tool.json — title + parameters JSON Schema for agents.