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CALCPARK

Video to MP3 Converter

Pull the audio track out of a video and save it as MP3 in your browser: LAME VBR or a fixed bitrate up to 320 kbps, optionally just a part of it. Nothing is uploaded.

Files stay on your device
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How to use it

  1. Drop a video or choose one. Its length appears under the file name once the browser has read the header.
  2. Pick an MP3 preset – keep V2 unless you need a fixed bitrate – and tick “Extract only a part” to set a range.
  3. Press Extract MP3. The progress bar covers the encode; the first run also downloads the engine.
  4. Listen to the preview, check the size and bitrate, then download.

Example

A 12-minute 720p lecture recording (180 MB, AAC 128 kbps audio) extracted with V2 takes around 40 s on a laptop and gives a 16 MB MP3 with an average bitrate near 185 kbps. The same track at 128 kbps constant is 11 MB; at 320 kbps it is 28 MB without sounding better than the AAC source, which was already lossy.

What FFmpeg does

The tool runs the WebAssembly build of FFmpeg in a Web Worker with one command:

ffmpeg [-ss START -t LENGTH] -i input.mp4 -vn -map 0:a:0 -c:a libmp3lame -q:a 2 -id3v2_version 3 output.mp3
  • -vn drops the picture and -map 0:a:0selects the first audio stream explicitly, so a silent video fails with a clear “no audio track” message instead of an empty file.
  • -c:a libmp3lame re-encodes with LAME. -q:a 0/2/4 are the VBR presets V0 (≈245 kbps), V2 (≈190 kbps) and V4 (≈165 kbps); -b:a 320k/192k/128k give a constant bitrate. MP3 cannot hold AAC or Opus data as-is, so an encode is always needed.
  • -ss and -t before -i limit the range; because the audio is decoded anyway, the cut is sample-accurate.
  • -id3v2_version 3 writes ID3v2.3 tags, the version Windows Explorer and older players read. Title and artist tags from the source container are carried over; embedded cover art is not.

Sample rate and channel count follow the source (typically 48 kHz stereo from cameras, 44.1 kHz from music). The engine is single-threaded and limited to 2 GB of memory, so keep inputs under a few hundred MB.

Sources: FFmpeg – libmp3lame encoder options, Hydrogenaudio – LAME VBR presets and typical bitrates, ffmpeg.wasm documentation.

Questions

VBR or 320 kbps – which should I choose?
VBR V2 for almost everything: it spends bits where the music needs them and averages about 190 kbps. Choose 320 kbps constant only when a platform or device requires a fixed bitrate, and 128 kbps for speech where size matters more than fidelity.
Will the MP3 sound better than the video’s audio?
No. Video audio is usually AAC or Opus, already lossy; MP3 encoding adds a second lossy step. V2 keeps that loss inaudible for most people, but a higher bitrate cannot restore detail the source never had.
Why does it say the video has no audio track?
Screen recordings, time-lapses and some exports contain no audio stream at all, and some containers hold audio in a codec the browser build cannot decode. Open the file in VLC and check Codec information to see what it contains.
Is the video uploaded?
No. The video is read into the FFmpeg engine inside your browser; the only network traffic is the engine itself (about 32 MB from the unpkg CDN, cached afterwards).