Video Format Converter - MP4, WebM, MOV, AVI, MKV

The converter runs FFmpeg compiled to WebAssembly, so the whole transcode happens in your browser and the file is never uploaded. Transcoding means the source is decoded to raw frames and re-encoded into the target codec, which is lossy for any lossy-to-lossy conversion because each encode-decode cycle discards some information that cannot be recovered. Converting once is fine; round-tripping the same file through several formats accumulates visible generation loss after a few cycles.

The audio codec is chosen automatically to match the container rather than being independently selectable: MP4, MOV, and MKV get AAC at 128 kbps, WebM gets Opus, OGG gets Vorbis, and AVI gets MP3. So you pick the container and the converter supplies a codec pairing that container supports, which avoids producing files that some players cannot open.

Quality is controlled by three presets rather than a continuous slider. Fast uses CRF 28 with the ultrafast x264 preset for the smallest files and quickest encode, Balanced uses CRF 23, and Quality uses CRF 18 with the fast preset for the best-looking output at a larger size. The platform shortcuts (YouTube, Instagram, Twitter/X, iPhone, Android, Web/HTML5) are convenience buttons that pick a suitable container and one of those three quality tiers; they do not impose platform-specific resolution caps or bitrate ceilings, so confirm the upload page if a platform has a strict size limit. For MP4, MOV, and MKV output the converter also forces even dimensions (required by libx264) and yuv420p pixel format for maximum player compatibility, and adds +faststart to MP4 so it begins playing before fully downloaded.