How It Works

This tool converts video and audio files entirely inside your browser using Mediabunny, a zero-dependency TypeScript library that handles container multiplexing / demultiplexing and codec encoding / decoding via the browser’s built-in WebCodecs API. Your files never leave your device.

Supported Input Formats

MP4, MOV, WebM, MKV, MP3, WAV, OGG, FLAC, ADTS, MPEG-TS — and any other container Mediabunny can demux.

Supported Output Formats

| Format | Extension | Best for | |--------|-----------|----------| | MP4 | .mp4 | Universal video — widest device & browser support | | WebM | .webm | Web video — open format, great compression | | MKV | .mkv | High quality video with multiple tracks | | MOV | .mov | Apple QuickTime video | | MP3 | .mp3 | Compressed audio — small files, universal support | | WAV | .wav | Uncompressed audio — lossless, large files | | OGG | .ogg | Open-source compressed audio | | FLAC | .flac | Lossless compressed audio |

Options

| Option | Description | |--------|-------------| | Output Format | Choose the target container format. Audio-only formats (MP3, WAV, OGG, FLAC) automatically discard the video track. | | Extract audio only | When selected for a video-capable output format, the video track is discarded and only the audio stream is written. | | Limit max width | Scales the video down proportionally so that its width does not exceed the specified pixel value. The aspect ratio is preserved. |

Implementation Details

Mediabunny is a pure TypeScript library with zero dependencies. It transmuxes or transcodes using WebCodecs when the source codec is not directly supported by the output container. In many cases (e.g. MP4 → WebM with VP8/VP9 source), the conversion is a fast transmux with no re-encoding.

Processing steps:

1. The file is wrapped in a BlobSource (lazy streaming reads — never fully buffered).
2. Input probes the container format and exposes track metadata.
3. Output is configured with the chosen output format and a BufferTarget.
4. Conversion.init() analyses the tracks, decides whether to transmux or transcode, and optionally sets up a resize pipeline.
5. conversion.execute() streams the conversion, calling onProgress at each step.
6. On completion the in-memory buffer is wrapped in a Blob for download.

Privacy

All processing runs locally in your browser tab. No file data or metadata is ever sent to any server.