How do I convert a video online for free without uploading it?

Drop one video into the box above, choose an output format and a quality preset, then press Convert video. FFmpeg compiled to WebAssembly re-encodes the file inside the tab, so nothing is uploaded. The first run downloads roughly 31MB of engine code, which the browser then caches.

Which output formats can I convert to?

Five: MP4, WebM, MKV, MOV and AVI. MP4, MKV and MOV are encoded with H.264 video and AAC audio at 128 kbps; WebM uses VP8 video with Vorbis audio; AVI uses the legacy MPEG-4 Part 2 codec with MP3 audio for old players and hardware.

Which format should I pick for maximum compatibility?

MP4. H.264 with AAC audio plays on effectively every browser, phone, smart TV, editor and social platform, and this tool adds the faststart flag so the file begins playing before it has fully downloaded. Only choose AVI if a specific piece of legacy hardware demands it.

What input video formats are supported?

MP4, MOV, WebM, AVI, MKV, M4V, TS, 3GP, FLV and WMV. Anything FFmpeg can demux will generally work, but exotic or DRM-protected files can fail. If a conversion errors out, the file is usually using a codec the WebAssembly build was not compiled with.

Is there a file-size limit?

Yes — 500MB, and the tool refuses larger files with a clear message rather than crashing the tab. That ceiling exists because the whole video is held in browser memory during conversion. Trim the clip first if you are over it, or compress it before converting.

Why does converting to WebM take so much longer?

Because VP8 encoding is simply slower than H.264, and the engine runs on a single CPU thread in WebAssembly with no GPU acceleration. A clip that converts to MP4 in a couple of minutes can take several times that as WebM. Choose MP4 unless you specifically need WebM.

Will converting reduce the video quality?

Every conversion here re-encodes, so there is some generation loss. The High quality preset keeps it visually hard to spot on normal viewing; Balanced is the default and right for most uses; Smaller file is visibly softer on detailed footage. To change container without re-encoding at all, use the remux tool.

Why is my MOV or MKV file not playing on Windows?

Containers and codecs are separate problems. iPhones record MOV and screen recorders often write MKV, and while both can hold H.264, Windows and Android players frequently refuse the container itself. Converting to MP4 rewraps and re-encodes the streams into the combination those players expect.

Video Converter

Convert video files between MP4, WebM, MOV, AVI and MKV online free using FFmpeg. No upload required — instant, private, in-browser.

Files never leave your deviceInstant — no upload waitFree, no sign-up

Choose a video or drag & drop it hereMP4, MOV, WebM, MKV, AVI, FLV, WMV… converted on your device, never uploaded

or import from

A video converter re-encodes a clip into a different container and codec so it plays where you need it. This one converts to MP4, WebM, MKV, MOV or AVI entirely inside your browser using FFmpeg compiled to WebAssembly — no upload, no sign-up, no watermark, up to 500MB per file.

How to convert a video in your browser

Drop one video in — MP4, MOV, WebM, MKV, AVI, M4V, TS, 3GP, FLV or WMV, up to 500MB.
Pick the output format and a quality preset: High, Balanced or Smaller file.
Press Convert video and keep the tab open. A progress bar tracks the encode.
Check and download. Before and after sizes are shown side by side, with an inline player for MP4, MOV and WebM results.

MKV and AVI results skip the preview player, because browsers cannot play those containers natively — the file itself is fine, it just has to be opened in a desktop player. That is the honest reason, not a limitation of the conversion.

What each output format actually contains

Codecs and settings applied per output format.
Format	Video codec	Audio codec	Quality preset applies	Best for
MP4	H.264, faststart enabled	AAC 128 kbps	Yes	Everything — the safe default
MOV	H.264, faststart enabled	AAC 128 kbps	Yes	Apple editing workflows
MKV	H.264	AAC 128 kbps	Yes	Desktop players, archiving
WebM	VP8	Vorbis	Yes, but slow	Embedding in HTML5 pages
AVI	MPEG-4 Part 2, fixed quality	MP3 128 kbps	No	Legacy players and hardware only

Two details worth reading twice. WebM here is VP8 with Vorbis, not the newer VP9 or AV1 — it is broadly compatible but not the smallest option available today. And AVI ignores the quality preset entirely, because it encodes at a fixed MPEG-4 quality level chosen for compatibility with players old enough to need AVI in the first place.

Choosing a quality preset

The three presets map to constant-rate-factor values, which is the standard way to ask an H.264 encoder for a quality level rather than a bitrate. High uses CRF 19,Balanced uses CRF 24 and is the default, and Smaller file uses CRF 29. Lower numbers mean better quality and bigger files. Balanced is genuinely the right answer for most clips; reach for High only when the footage is detailed and destined for a large screen.

Output dimensions are rounded down to the nearest even number, because H.264 requires it. A 1921-pixel wide source becomes 1920 — a single column of pixels, not something you will notice, but it explains any one-pixel difference you spot in the file properties.

What running FFmpeg in the browser really costs

The trade-off is honest and worth stating up front. Your video never leaves the device, which is the whole point, but the encoding happens on one CPU thread with no GPU acceleration — the single-threaded WebAssembly build is required because the site does not set the cross-origin isolation headers the multi-threaded build needs. Expect it to be slower than a desktop app, and noticeably slower again for WebM.

The engine itself is roughly 31MB, downloaded on your first conversion and cached by the browser afterwards. Worth knowing before you start on mobile data. Keep the tab in the foreground while it works; backgrounded tabs get throttled by the browser and the encode will crawl.

How this compares to cloud converters and desktop software

Converting a single clip, three ways.
	ToolJiffy	Typical online converter	Desktop software
Video uploaded to a server	No	Yes	No
Sign-up	No	Often above a size or count limit	Install, sometimes licence
File-size limit	500MB	Commonly 500MB–1GB on free tiers	None practical
Watermark	Never	Sometimes on free tiers	No
Speed	Single CPU thread, no GPU	Fast server-side	Fastest, uses all cores
Queue or daily cap	No	Common	No
Price	Free, unlimited	Free tier then subscription	Free to paid

When another tool is the better answer

If the container is wrong but the codecs are already fine — an MKV holding H.264 and AAC that you want as MP4 — remux video copies the streams across without re-encoding, which is far faster and loses nothing. If the file is simply too big, thevideo compressor targets size directly rather than format. To shorten a clip before converting it, trim video does that in one pass, andresize video handles dimensions.

For pulling media out of a clip rather than reformatting it, video to MP3extracts the audio track, video to GIF makes a looping animation, andvideo screenshot grabs a still frame at full resolution.

Frequently Asked Questions

How do I convert a video online for free without uploading it?
Drop one video into the box above, choose an output format and a quality preset, then press Convert video. FFmpeg compiled to WebAssembly re-encodes the file inside the tab, so nothing is uploaded. The first run downloads roughly 31MB of engine code, which the browser then caches.
Which output formats can I convert to?
Five: MP4, WebM, MKV, MOV and AVI. MP4, MKV and MOV are encoded with H.264 video and AAC audio at 128 kbps; WebM uses VP8 video with Vorbis audio; AVI uses the legacy MPEG-4 Part 2 codec with MP3 audio for old players and hardware.
Which format should I pick for maximum compatibility?
MP4. H.264 with AAC audio plays on effectively every browser, phone, smart TV, editor and social platform, and this tool adds the faststart flag so the file begins playing before it has fully downloaded. Only choose AVI if a specific piece of legacy hardware demands it.
What input video formats are supported?
MP4, MOV, WebM, AVI, MKV, M4V, TS, 3GP, FLV and WMV. Anything FFmpeg can demux will generally work, but exotic or DRM-protected files can fail. If a conversion errors out, the file is usually using a codec the WebAssembly build was not compiled with.
Is there a file-size limit?
Yes — 500MB, and the tool refuses larger files with a clear message rather than crashing the tab. That ceiling exists because the whole video is held in browser memory during conversion. Trim the clip first if you are over it, or compress it before converting.
Why does converting to WebM take so much longer?
Because VP8 encoding is simply slower than H.264, and the engine runs on a single CPU thread in WebAssembly with no GPU acceleration. A clip that converts to MP4 in a couple of minutes can take several times that as WebM. Choose MP4 unless you specifically need WebM.
Will converting reduce the video quality?
Every conversion here re-encodes, so there is some generation loss. The High quality preset keeps it visually hard to spot on normal viewing; Balanced is the default and right for most uses; Smaller file is visibly softer on detailed footage. To change container without re-encoding at all, use the remux tool.
Why is my MOV or MKV file not playing on Windows?
Containers and codecs are separate problems. iPhones record MOV and screen recorders often write MKV, and while both can hold H.264, Windows and Android players frequently refuse the container itself. Converting to MP4 rewraps and re-encodes the streams into the combination those players expect.