# Convert MKV, MOV, AVI & WebM to MP4 — Free, In Browser, No Upload

> Loft Video Converter is a free online video converter that turns MKV, MOV, AVI, and WebM files into MP4 entirely in your browser — no upload, no watermark, no install. When the source codecs are already MP4-legal it does a fast lossless stream-copy (instant); when a codec change is needed it re-encodes via WebCodecs. Handy because Apple won't add MKV support and QuickTime can't open AVI. Files never leave your device.


Live tool: https://lofttools.com/tools/audio-video-tools/video-converter

Category: Audio and Video

## How it works

1. **Upload videos** — Drag and drop MKV, MOV, AVI, or WebM files (up to 500 MB each)
2. **Choose mode** — Select Fast (lossless copy) or Re-encode for maximum compatibility
3. **Download** — Get MP4 file(s) — batch converts download as a ZIP

## FAQ

### Why won't my MKV play on Apple devices?

Apple's QuickTime and iOS do not support the MKV container. This tool rewraps the video into an MP4 — using a fast lossless copy when the video codec is already H.264 or H.265, so there is no quality loss and conversion is nearly instant.

### What is the difference between Fast and Re-encode?

Fast mode stream-copies the video into an MP4 container without re-encoding — no quality loss, no waiting. Re-encode mode transcodes the video to H.264 via WebCodecs, which takes longer but maximises compatibility with older devices and media players.

### Which formats can I convert?

MKV (.mkv), MOV (.mov), AVI (.avi), WebM (.webm), and MP4 (.mp4) — up to 500 MB each. Batch mode converts multiple files at once and packages them as a ZIP.

### Does the video leave my device?

No. Conversion runs entirely in your browser using WebCodecs. Your files are never uploaded to a server.

### Will Fast mode always work?

Fast (stream-copy) works when the video codec is already MP4-compatible (e.g., H.264 in an MKV). If the codec is not MP4-legal (e.g., VP9 in WebM) the tool automatically falls back to re-encoding so you always get an MP4.

## Tips

- **Fast copy is lossless** — When your source codec is H.264 or H.265, Fast mode rewraps the video without re-encoding — zero quality loss and conversion is nearly instant.
- **Re-encode for old devices** — Smart TVs, older Android phones, and some media players need a plain H.264 MP4. Re-encode mode produces the most compatible output.
- **Batch convert with one ZIP** — Drop multiple files at once. All converted MP4s are packaged into a single ZIP for easy download.

## Privacy — what we do not do

This tool runs entirely in the browser via WebAssembly. Your file never reaches a Loft Tools server. Specifically:

- **No upload.** The file bytes load into the browser tab's memory and process on your own CPU. Open DevTools → Network and observe zero outbound requests carrying file data while Convert MKV, MOV, AVI & WebM to MP4 — Free, In Browser, No Upload runs.
- **No AI training on your file.** Loft does not train models. We could not train on a file we cannot see.
- **No content scanning.** No virus, copyright, or content-moderation pass against your file. The bytes are not accessible to us.
- **No server-side log of file contents, filenames, or EXIF metadata.** Cloudflare edge captures URL and truncated IP for abuse defense (standard CDN behaviour). Cloudflare Web Analytics records anonymous page hits, no cookies, no PII. Nothing about your file content reaches any log.
- **No retention.** Close the tab and the file leaves browser memory. No backups exist on our side because no copy ever existed on our side.
- **No account.** No email, no signup, no auth, no telemetry tied to you.
- **Offline-capable after first visit** (PWA). Once you've loaded a tool, it caches; later sessions work without internet. For high-sensitivity files, run the tool once online to warm the cache, then disconnect before processing.

Compare with upload-based services: each transmits your file to a processing server. Even over HTTPS, each has logs, retention windows, and subpoena exposure. Loft has none of these because the server architecture does not include your file.

## More

- All tools: https://lofttools.com/tools
- Category: https://lofttools.com/tools/audio-video-tools
- LLM index: https://lofttools.com/llms.txt