Video Converter
MP4 / AVI / MKV / MOV / WebM interconversion with automatic lossless remux, fully local
Drag & drop files here
or browse files
Converts between MP4 / AVI / MKV / MOV / WebM, also reads FLV & friends
About this tool
Video conversion solves two problems: files that will not play on your device and files that are awkward to share. Old camcorder and surveillance .avi clips stall on phones, .mkv movies refuse to play on TV boxes, and iPhone .mov files are heavy on Windows. This tool converts between MP4, AVI, MKV, MOV and WebM, and also reads FLV, WMV, MPG and TS sources - with AVI to MP4 and MKV to MP4 being the two most requested pairs.
There are two ways to convert. The first is a lossless remux: when the video stream inside your file (say H.264 + AAC) is already allowed in the target container, the tool just swaps the wrapper - no re-encoding, bit-identical quality, done in seconds. It inspects your upload first and always prefers this path. The second is re-encoding, needed for legacy codecs like DivX/Xvid: FFmpeg rebuilds the file as H.264 + AAC at high-quality CRF settings that are very hard to tell apart from the original.
Everything runs on FFmpeg compiled to WebAssembly inside your browser, so your video never leaves the device - nothing is uploaded or stored, which matters a lot for home movies and surveillance footage.
Features
- Convert between MP4, AVI, MKV, MOV and WebM, reading FLV/WMV/MPG/TS sources too
- Automatic lossless stream-copy (remux) when codecs allow it: zero quality loss, finishes in seconds
- Silent-free fallback to high-quality H.264/VP9 re-encoding - you always see which mode ran
- Optional faststart on MP4/MOV output for web streaming (play while downloading)
- Processed locally in your browser - no upload, no sign up, no watermark, no limits
How to use
- Drop your AVI / MP4 / MKV / MOV file into the box (or click to browse) - it is inspected automatically
- Choose the target format and keep the lossless-remux and faststart switches as needed
- Click Convert and watch the live progress; you can cancel at any time
- Preview the result, compare sizes and download the converted file
Frequently asked questions
- Does converting AVI to MP4 lose quality?
- It depends on the codec inside the AVI. If it already contains H.264 video the tool performs a lossless remux: the streams are copied untouched, so the MP4 is bit-identical in quality and done in seconds. Only legacy DivX/Xvid files must be re-encoded, in which case high-quality CRF settings are used and the difference is nearly invisible. The result page always tells you which mode was used.
- What is a remux and how is it different from transcoding?
- A video file is a container (the .mp4/.avi/.mkv wrapper) holding encoded audio and video streams. A remux copies those streams into a new wrapper with no quality change and almost no time. Transcoding decodes and re-compresses the streams, which costs time and a little quality. The tool tries remux first and only transcodes when required.
- Can I convert MP4 back to AVI or MKV?
- Yes - direction does not matter. MP4 to MKV with H.264 + AAC usually remuxes losslessly; MP4 to AVI remuxes where possible or re-encodes to an Xvid/MPEG-4 combo that old devices accept.
- Why is my conversion slow?
- Remuxes finish in seconds; only re-encoding takes time. Browser FFmpeg encodes on the CPU (no GPU access), so expect roughly 1-5x the clip duration for 1080p material. Keep single jobs under about 1 GB / 1 hour, or split long recordings first.
- Is my video uploaded anywhere?
- No. There is no backend that could receive it - all processing happens in your browser memory. The first run downloads a ~31 MB FFmpeg engine from a CDN (cached afterwards); once loaded, conversion even works offline.