Step 1: Provide your MP4 files using the button above or by toss and let go.
Step 2: Click the 'Convert' button to start the conversion.
Step 3: Fetch your converted WebM files.
MP4 to WebM Conversion FAQ
How do I convert MP4 to WebM without re-encoding the video stream?
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There is no stream-copy switch on this page. A few pairs copy a compatible video stream into the WebM container without re-encoding it, MKV to MP4 among them, which is quick and loses no quality. Most pairs re-encode the video. Almost every MP4 in the wild is H.264 video with AAC audio; the container also legally holds HEVC, AV1 and VP9. WebM is deliberately narrow: VP8 or VP9 video (AV1 more recently) with Vorbis or Opus audio, and nothing else.
Both MP4 and WebM are modern containers — which should I actually keep?
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Keep whichever matches where the file is going, because neither is better in the abstract. One of these two is built for playback compatibility and the other for holding everything a file might contain, and they trade against each other exactly along that line. The pragmatic answer for most libraries is to archive in the feature-rich container and export to the compatible one on demand. MP4 is the safest possible delivery target — every phone, browser, console, editor and Smart TV built in the last decade plays it without extra software. WebM plays natively in every modern browser with no plugin, no licence fee and no patent exposure, which makes it the default for web-embedded video.
Will multi-track audio survive MP4 to WebM conversion?
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Usually not. Most conversions keep one audio track, the one with the most channels (normally the main mix), re-encoded for the WebM container, so commentary and alternate-language tracks are dropped. AVI, WMV, MPEG, FLV, VOB and M4V to MKV keep every track, and so does MP4 to MOV. To keep a different track, remux the MP4 with that track first (VLC or ffmpeg can do this), then convert it. WebM is a strict subset of Matroska that Google published in 2010 specifically to give HTML5 video a royalty-free container.
Are subtitle tracks preserved when converting MP4 to WebM?
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On some pairs. MP4 to MOV keeps every text subtitle track. AVI, WMV, MPEG, FLV, VOB and M4V to MKV keep every subtitle track: text subtitles are copied or converted to SRT, and picture-based subtitles such as DVD or Blu-ray ones are copied as they are. MP4, MOV and WebM to MKV keep only the first subtitle track (as ASS), and MP4 to WebM keeps the first one as WebVTT. Other pairs, including MKV to MP4 or MOV and WebM to MP4, drop subtitle tracks, and the converter does not burn them into the picture. Subtitles that are already burned in stay, because they are part of the video frames.
What about MKV attachments (fonts, cover art) when going MP4 to WebM?
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MKV is the only mainstream container that stores arbitrary attached files (TTF fonts for ASS subs, JPG cover art, fan-translated PDF inserts). Going from MP4 to WebM drops these attachments when WebM is not MKV — the elementary streams convert, but the attached payload stays in the source. Keep MP4 as a backup if you depend on attached fonts.
Which codec does the WebM output use by default?
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It depends on the WebM container. MP4, MOV and MKV output use H.264, which plays on practically every phone, browser and TV. WebM output uses VP9. AVI, WMV and MPEG output use the older codecs those formats were designed for. WebM is a poor fit anywhere outside a browser — video editors, phones’ native galleries and Smart TVs largely ignore it.
How does HDR (HDR10, Dolby Vision) survive MP4 to WebM?
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There is no HDR processing or tone mapping. When the video stream is copied (MKV to MP4 or MOV with the default settings), HDR10 passes through as it is. When the video is re-encoded, the HDR10 mastering metadata is dropped and Dolby Vision or HDR10+ data is not kept, and with a Quality, Resolution or Frame Rate setting some pairs also reduce the video to 8-bit colour, so an HDR MP4 can look washed out in the WebM.
Why is my WebM file smaller / larger than the MP4 after conversion?
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It depends on what happens to the video. MKV to MP4 or MOV with the default settings copies the video stream unchanged, so the size stays close to the source. Most other pairs re-encode it: a high-bitrate MP4 usually comes out smaller, while an already heavily compressed one can grow. Smaller File under Quality gives the smallest output, and H.265 in the Codec setting (MP4, MOV and MKV) is usually smaller than H.264 at similar quality but plays on fewer devices.
Does the MP4 to WebM converter handle 4K / 8K / 60fps content?
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The converter has no resolution cap of its own; the limit is the upload size allowed on your plan, and 4K, 8K and 60 fps files keep their resolution and frame rate unless you change them. MKV to MP4 or MOV with the default settings copies the video stream, which is quick at any resolution. Other pairs re-encode on CPU and the time grows with the pixel count, so a long 4K or 8K file takes much longer than the same length in 1080p.
Is my MP4 file private during WebM conversion?
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Yes. Uploaded MP4 files are processed on our own conversion servers, no person reviews them, and they are never shared. The upload and the converted WebM are both deleted automatically about 24 hours after the conversion, which leaves time to download the result. See /privacy/ for the full policy.
