WebM to MP4 Converter

WebM to MP4, in your browser. Nothing ever uploads.

Drop a WebM below — screen recordings, browser captures and web clips converted to MP4 entirely on your device.

  • Zero uploads — verifiable
  • Unlimited free use
  • Batch up to 5 files
  • H.264 + AAC output, plays anywhere

Convert WebM to MP4

Add your WebM files

Drag & drop WebM files here

or browse your files · up to 5 files, 200 MB each

Converter loads only when you convert your first file — the page stays light until then.

    No files yet. Everything stays on this device. Downloads start instantly.
    Conversion settings
    Conversion mode

    Automatic: H.264 WebM files remux in seconds with zero quality loss; VP8/VP9/AV1 files are transcoded to H.264 + AAC at your chosen quality below.

    Transcode quality (only used when re-encoding is needed)

    Remuxed files ignore this setting entirely — a stream copy has no quality setting to choose.

    What always happens

    Subtitles are dropped (MP4 players handle them inconsistently). Only the first video track and first audio track are kept. Audio that cannot be copied (Opus, Vorbis) is converted to AAC at 128 kbps. Output is H.264 + AAC in an MP4 with fast-start, so it plays before fully downloading.

    Privacy you can verify, not just trust

    Most online WebM to MP4 converters upload your file to their servers first — and some keep a download link live for 30 days. This one can't: the converter runs entirely in your browser. Your videos are never sent anywhere — the only requests to other sites are the site's own analytics, which count page views — and it uploads nothing, ever. The only file fetched after load for the conversion itself is the encoder (~31 MB, from this same site, once, on your first convert) — it carries no video data. Don't take our word for it:

    External requests during processing: 0 (zero — as it should be)
    1. Press F12 to open developer tools, then the Network tab.
    2. Convert any WebM above. Watch: apart from the site's analytics, the only request is the encoder file from this site — no uploads, and no video data ever leaves your device.
    3. Extra credit: disconnect your internet after this page loads — conversion still works.

    How to convert WebM to MP4 without uploading it

    WebM is the web's native video format — efficient, royalty-free, and the default output of Chrome tab captures, Loom downloads, OBS browser sources and most screen recorders. The problem starts the moment the recording leaves the browser: phones' galleries, smart TVs, game consoles, video editors and presentation apps mostly refuse WebM, and almost all of them expect one format — MP4 with H.264 video and AAC audio. Converting WebM to MP4 is usually just a matter of putting your recording into the wrapper every device understands.

    This tool does exactly that, on your own device. When you drop a WebM here, your browser:

    1. Loads a real video converter (ffmpeg, compiled to WebAssembly) — but only when you convert your first file, so the page itself stays light.
    2. Reads the file's streams — which video codec, which audio codec, whether there are subtitles — and decides the fastest honest path for that file.
    3. Remuxes when it can: if the WebM already holds H.264 video with AAC audio (rare — some recorders write H.264 into WebM), both streams are copied bit-for-bit into a new MP4. No decoding, no re-encoding, no quality loss — a file that would take minutes to re-encode finishes in seconds.
    4. Transcodes only what must change: VP8, VP9 or AV1 video is re-encoded to H.264, and Opus or Vorbis audio to AAC (128 kbps). Streams that are already compatible are still copied, never re-encoded.
    5. Hands you an MP4 as a download, with fast-start enabled so it begins playing before it has fully downloaded. Your original WebM is never modified.

    Why do so many apps reject WebM?

    Because WebM was designed for browsers, not devices. Its codecs — VP8, VP9 and AV1 for video, Opus and Vorbis for audio — are royalty-free, which is why Chrome, YouTube, Discord and screen recorders love them. But the hardware decoders inside phones, TVs and consoles were built around H.264 and AAC, and most editors and presentation tools never added WebM support at all. An MP4 with H.264 + AAC is the one format the whole ecosystem agrees on, which is why converting is usually the fix, not a workaround.

    When is remuxing possible?

    Only when the WebM already holds H.264 video with AAC audio. That happens with some recorders — Chrome's MediaRecorder, for example, can write H.264 into a WebM container when the hardware encoder offers it — but it is the exception, not the rule. The tool checks the codecs first and tells you which path each file took, instead of re-encoding everything the way most online converters do.

    When transcoding is unavoidable

    Most WebM files hold VP8, VP9 or AV1 video (common in browser captures and files downloaded from the web) and Opus or Vorbis audio. None of those have a legal home in a broadly playable MP4, so they must be re-encoded. That takes roughly real time or slower in a browser tab, and it loses a little quality — the tool uses CRF 20 by default, where the loss is hard to spot, and says so plainly on the file card instead of pretending the conversion was lossless.

    Honest limitations

    Most WebM files transcode, not remux

    Remuxing only works when the WebM already holds H.264 + AAC, which is rare. Expect a transcode for ordinary VP8/VP9/AV1 recordings — slower, and with a small quality loss.

    Subtitles are dropped

    MP4 players handle subtitle tracks inconsistently, so this tool leaves them out rather than burning them into the picture. Keep the original WebM if you need the subtitles.

    Only the first audio track

    If your WebM has several audio tracks, only the first is kept. The rest are dropped, and the card says so.

    Transcoding is slow and slightly lossy

    VP8/VP9/AV1 video and Opus/Vorbis audio must be re-encoded. Expect roughly real time or slower in a browser tab, and a small quality loss — the card tells you when this happened.

    200 MB per file, 5 files per batch

    The converter holds the whole file in tab memory, so multi-GB files — a long screen recording — can crash the tab. Large files belong in a desktop converter like HandBrake.

    Output is always H.264 + AAC

    Every MP4 this tool produces is H.264 video with AAC audio, so it plays on phones, TVs, browsers, consoles and old laptops alike — the whole point of converting.

    Frequently asked questions

    How do I convert WebM to MP4 without uploading it anywhere?

    Use a tool that converts files locally in your browser. This converter loads ffmpeg (compiled to WebAssembly) into your device, reads your WebM's video and audio streams, and either copies them straight into an MP4 container (remuxing) or re-encodes them to H.264 + AAC — all with JavaScript running on your machine. No file data is sent to any server; verify it in your browser's Network tab.

    What is remuxing, and why is it faster than converting?

    Remuxing changes only the container, not the video itself. If your WebM already holds H.264 video with AAC audio, those streams are already legal MP4 contents, so the tool just copies them into a new MP4 file — no decoding, no re-encoding, done in seconds. This is rare for WebM: most WebM files hold VP8, VP9 or AV1, which cannot live in a broadly playable MP4 and must be transcoded. This tool remuxes whenever it can and only re-encodes the streams that truly need it.

    Will converting WebM to MP4 lose quality?

    Not when the file is remuxed — remuxing copies the video and audio bit-for-bit, so the MP4 is identical in quality to the WebM. But most WebM files cannot remux: VP8, VP9 and AV1 video (and Opus/Vorbis audio) must be re-encoded to H.264 + AAC, which loses a little quality — the tool tells you which path each file took and uses CRF 20 by default, a setting where the loss is hard to spot.

    What happens to subtitles and extra audio tracks?

    Subtitles are not carried over. MP4 players handle subtitle tracks inconsistently, so this tool leaves them out rather than burning them into the picture or producing a file some players mishandle — each file card says so plainly when a subtitle track is dropped. Only the first video track and the first audio track are kept; if your WebM has several audio tracks (for example, multiple languages), the rest are dropped. Keep the original WebM if you need the subtitles or the other languages.

    Will the MP4 play on my phone, TV, or older device?

    Yes. The output is always H.264 video with AAC audio — the one combination every device understands. WebM plays reliably in browsers but is rejected by most phones' galleries, TVs, game consoles, editors and presentation apps, while H.264 MP4 plays on practically everything.

    How big can the WebM file be?

    200 MB per file, up to 5 files per batch. The converter runs entirely in your browser tab and holds the whole file in memory, so a larger input can crash the tab — multi-GB files, like a long screen recording, exceed what a browser tab can practically hold and need a desktop converter (HandBrake or Shutter Encoder, both free). There is no duration limit for remuxed files, but transcoding a long file is slow — roughly real time or slower — so files over 30 minutes that need transcoding come with a warning.

    Does this WebM to MP4 converter upload my files?

    No. All conversion happens on your device with ffmpeg.wasm, downloaded from this site once (about 31 MB, in two parts) and then run locally. Your files are never sent to any server; the only network requests on this page are the site's own analytics (Google Analytics and a Cloudflare beacon), which load when the page opens and never see your files. You can verify it in your browser's DevTools Network tab — the page shows a live counter of requests during processing, which stays at zero while a file converts.