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100% free · No file size limit · No watermark

Video Converter

Convert any video to MP4, MOV, WebM, MKV, or AVI — with optional resolution downscale and rotation/flip.

100% freeNo file size limitNo watermarkNo sign-up
  1. 1Pick file
  2. 2Configure
  3. 3Download
Supported: MP4, MOV, WebM, MKV, AVI, M4V, FLV. Most browsers run the conversion on your GPU (WebCodecs hardware H.264) — typically real-time or faster. Firefox falls back to libx264 which is slower but still works.
  • Files never leave your browser — processed entirely on your device
  • No upload, no queue, no waiting for a worker to free up
  • No file-size cap from us — limit is your device's RAM

About Video Converter

AntiUpload's Video Converter is a fully in-browser format converter for video files. Drop in an MP4, MOV, WebM, MKV, AVI, M4V, or FLV file and you get back any of the five mainstream output containers — re-encoded with H.264 for the MP4 / MOV / MKV / AVI family, VP9 for WebM. The whole pipeline runs on your device using FFmpeg compiled to WebAssembly plus, on supporting browsers, the WebCodecs API for hardware-accelerated encoding via your GPU or device SoC. There is no upload, no queue, no per-file size limit imposed by us — the only ceiling is your device's available RAM.

The hook is simple: cloud-based converters (CloudConvert, FreeConvert, OnlineConvert, Zamzar) cap free users at 100 MB, watermark the output, run users through a queue, and charge $9–$25/month to lift those limits. None of that economics applies to a tool that does the encoding on the user's hardware — there's no server CPU to charge for, no storage to amortise, no bandwidth bill. We pass those savings on as zero pricing.

When the converter detects a Chromium-based browser with WebCodecs and a hardware H.264 encoder, it routes encoding through the hardware path automatically — 5–20× faster than the software libx264 fallback, which is what every other in-browser converter relies on. Safari 17+ and modern Edge also qualify. Firefox and older browsers fall through to the libx264 path cleanly; the conversion still works, just slower. There is no manual setting — the runtime picks the fastest available path per-device.

How it works

  1. Drop a video into the pickerAccepts MP4, MOV, WebM, MKV, AVI, M4V, FLV. There's no size limit — drop a 4 GB drone clip or a 50 MB phone recording, same flow. Your file stays on your device.
  2. Pick output format + resolutionChoose MP4 (universal), MOV (Apple-friendly), WebM (open / web-native), MKV (permissive), or AVI (legacy). Optionally downscale to 1080p / 720p / 480p / 360p to shrink the file. Optionally rotate 90° / 180° / flip horizontal or vertical.
  3. Click ConvertOn Chromium + Safari 17+ with hardware H.264 encode, expect real-time or faster. On older browsers, expect ~1× realtime (a 60 sec clip takes ~60 sec). Progress bar shows live frame= updates.
  4. Download the resultWhen encoding finishes, the file is ready instantly — no upload-back round trip. Click download or hit "Process another file" to loop back to the picker.

When to use Video Converter

Phone video to web-friendly MP4 for upload
iPhones save .mov. Some platforms (older WordPress, Discord on Android, certain CMS uploaders) reject MOV. Convert to MP4 in 30 seconds locally rather than paying CloudConvert.
Screen recording (WebM) to MP4 for client review
Loom / Chrome screen capture often outputs WebM. Convert to MP4 for clients on Outlook, older Quicktime, or any pipeline that expects H.264.
MKV to MP4 for streaming to TV via Plex / Chromecast
MKV containers don't play on every TV firmware. Re-mux into MP4 (same H.264 codec, just a different wrapper) and casting works on every device.
Rotate a sideways phone video before sharing
Vertical phone clips that arrive rotated 90° in some apps. Re-encode with the 90° rotation baked in so every player shows it the right way up.
Downscale 4K source to 1080p to fit cloud-storage quota
A 4K phone clip is ~400 MB / minute. Downscale to 1080p first and the same minute drops to ~100 MB — fits Dropbox free quota, Discord Nitro upload, etc.

Frequently asked questions

How to convert a 5GB video for free online?
Drop it into our Video Converter at antiupload.com/video/video-converter. No size limit — your file stays on your device the whole time, encoded with your own CPU/GPU. Every other free converter (CloudConvert, FreeConvert, Zamzar) caps free users at 100 MB and asks for upgrades above that. Ours has no cap because we never receive the file in the first place.
Best no-watermark online video converter?
AntiUpload Video Converter produces clean output with zero watermarks, signups, or paywalls. The reason: we don't pay server costs to convert your file (your browser does the encoding), so there's no business case for upsells. Compare to Movavi / Wondershare / Veed which all watermark free tiers and charge $10-30/month to remove.
Is it really safe? My video has private content.
Yes — the conversion happens entirely on your device. Your file is never uploaded to our servers. Open the browser DevTools Network tab while converting: no requests for your file are made. The only network requests on first use are downloading the FFmpeg WASM engine (~12 MB) and the page JavaScript — neither of which contains your video.
How does the WebCodecs path differ from libx264?
WebCodecs lets the browser hand encoding to your device's hardware H.264 encoder (the same chip phones use to record video). This is 5-20× faster than software libx264 running in WASM. We use WebCodecs when available (Chrome, Edge, Brave, Safari 17+) and fall back to libx264 on Firefox / older browsers. Quality is comparable; speed is the difference.
Why does the converter run slower in Firefox?
Firefox's WebCodecs implementation lacks an H.264 encoder as of late 2025. We auto-detect this and route to libx264-in-WASM, which is software encoding and ~5-20× slower than hardware. Conversion still works — a 1-minute clip just takes ~5-15 minutes instead of 30 seconds. The fix would require Mozilla to ship hardware H.264 encoding, which has been on their roadmap for years.
Can I convert HEIC video / iPhone .mov to MP4?
Yes. iPhone .mov files are accepted; output to MP4 or any other format. Note that HEVC-encoded MOV files (the iPhone default since iOS 11) require a decoder we ship via FFmpeg.wasm — slower than H.264 source but supported.
Does it work on mobile?
Yes, on modern mobile browsers (iOS Safari 17+, Chrome / Edge for Android). Hardware encoding is available on most phones manufactured after 2019. Larger files (>500 MB) may exhaust mobile RAM; the desktop site is more reliable for big files.

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