Step 1: Provide your WebM 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 MKV files.
WebM to MKV Conversion FAQ
How do I convert WebM to MKV 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 MKV container without re-encoding it, MKV to MP4 among them, which is quick and loses no quality. Most pairs re-encode the video. WebM is deliberately narrow: VP8 or VP9 video (AV1 more recently) with Vorbis or Opus audio, and nothing else. MKV is codec-agnostic: H.264, HEVC, VP9 and AV1 video sit happily beside AAC, FLAC, Opus, DTS or Dolby audio in the same file.
Can WebM be converted to MKV without re-encoding the video?
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No, not on this page. WebM and MKV share the same underlying structure, but the converter re-encodes the video for this pair rather than copying the stream, so it takes longer than a container change and the picture is compressed again. Choose High Quality under Quality to keep the most detail. WebM is a strict subset of Matroska that Google published in 2010 specifically to give HTML5 video a royalty-free container. MKV is Matroska, an open container designed in 2002 with no licensing restrictions and no ceiling on what it can hold.
Can the MKV hold more than one audio track?
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Yes, and it is a real upgrade over WebM. MKV treats every audio stream as a first-class track, so an original-language mix, a dub and a director commentary can live in one file with the player switching between them on demand. MKV is the archival container of choice because it stores unlimited audio tracks, soft subtitles, chapter markers and cover art in one file.
Does MKV support chapter markers that WebM did not?
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It does. MKV stores chapters as container metadata, so a long recording can be navigated by section instead of by scrubbing a progress bar. WebM has nowhere to put that information, so the converted MKV starts with no chapters; add markers afterwards with a tool such as MKVToolNix or ffmpeg.
Can I still embed the file on a web page after converting WebM to MKV?
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Not directly. WebM plays inline in every browser; MKV does not, so a page embedding it falls back to a download link or an empty player frame. If the file is destined for a website, keep the WebM for the web and treat the MKV as the archive or editing copy. MKV has almost no native hardware support — phones, browsers and TVs usually need VLC or a remux before they will play it.
Will the MKV still play smoothly on a phone or a TV?
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It may not. WebM is decoded by dedicated silicon on phones, tablets and TVs, which is why it plays without flattening the battery. MKV typically falls back to software decoding on the same hardware — higher CPU load, a warmer device, and dropped frames on 4K material. For a device target, WebM is the safer container to stay in.
Will multi-track audio survive WebM to MKV 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 MKV 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 WebM with that track first (VLC or ffmpeg can do this), then convert it.
Are subtitle tracks preserved when converting WebM to MKV?
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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 WebM to MKV?
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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 WebM to MKV drops these attachments when MKV is not MKV — the elementary streams convert, but the attached payload stays in the source. Keep WebM as a backup if you depend on attached fonts.
Which codec does the MKV output use by default?
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It depends on the MKV 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.
How does HDR (HDR10, Dolby Vision) survive WebM to MKV?
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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 WebM can look washed out in the MKV.
