Video Converter

It depends on what you're converting. If you're only changing the container format (like MKV to MP4) without re-encoding the video stream, there is zero quality loss. The video data stays identical; only the wrapper changes. However, if you re-encode to a different codec or a lower bitrate, some quality loss is inevitable. Video compression is "lossy," meaning each round of encoding discards some information. The loss is usually negligible with modern codecs at reasonable settings, but converting the same file repeatedly (like photocopying a photocopy) will visibly degrade quality over time.

A container (MP4, MKV, WebM) is the file format that organizes and stores the video, audio, and metadata streams. A codec (H.264, H.265, VP9) is the algorithm that compresses and decompresses the actual video data. A single container can hold video encoded with different codecs. For example, an MP4 file might contain H.264 video, or it might contain H.265 video. The container determines compatibility with players and platforms; the codec determines quality and file size.

The format (container) itself doesn't determine quality -- the codec and encoding settings do. A poorly encoded MP4 will look worse than a well-encoded WebM. That said, for the best quality-to-size ratio with current technology, use H.265 or VP9. If you need the absolute best and have time for slow encoding, AV1 is the most efficient codec available. For raw, uncompressed quality (like in professional editing), formats like ProRes in MOV are used, but they produce enormous files.

Our converter uses FFmpeg compiled to WebAssembly (WASM), which lets the powerful FFmpeg video processing library run directly inside your web browser. When you upload a file, it stays on your computer -- the video data is processed locally using your CPU, never sent to any server. This approach is slower than a native desktop application (since WebAssembly can't access GPU hardware acceleration), but it means your files remain completely private. No upload, no server processing, no data retention.

With our tool, yes. Because the conversion happens entirely in your browser, your video files are never uploaded to a remote server. This is fundamentally different from most online converters, which require you to upload your file, process it on their servers, and then download the result. Those services do have access to your files. With browser-based conversion, the video never leaves your device, so there's no privacy risk and no upload wait time.

File size is primarily determined by the codec and the bitrate setting. If you convert from a highly compressed codec (like H.265) to an older one (like H.264 or MPEG-4), the output file will likely be larger because older codecs are less efficient. Conversely, converting from an older codec to a newer one may shrink the file. The resolution and duration also matter: a 4K video will always be larger than a 1080p version of the same clip. If your converted file is unexpectedly large, check whether the output codec is less efficient than the source.