Step 1: Share your WebM files using the button above or by drag and drop.
Step 2: Click the 'Transform' button to start the transformation.
Step 3: Grab your converted MKV files.
WebM to MKV Transformation FAQ
How do I re-encode WebM to MKV without losing video quality?
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Upload your WebM file and set Quality to High Quality in the conversion options. That re-encodes the video at the highest quality setting (CRF 18 for H.264 and VP9 output), which keeps the most detail at the cost of a larger file. The default, Balanced, uses the standard setting. The MKV output gets a codec its container supports: H.264 for MP4, MOV and MKV, VP9 for WebM. 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.
Which video codec does the MKV output use?
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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.
Will my audio track survive WebM to MKV conversion?
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Yes, the main audio track comes through, re-encoded to a codec the MKV container plays, for example AAC in MP4 and MOV or Opus in WebM. Most conversions keep only that one track (the one with the most channels), so alternate languages and commentary are dropped. MP4 to MOV, and AVI, WMV, MPEG, FLV, VOB or M4V to MKV, keep every audio track.
Can I keep the original framerate when converting WebM to MKV?
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Yes. The frame rate is kept unless you change it: a 24 fps WebM stays 24 fps in the MKV. The Frame Rate setting can also convert to 60, 30 or 24 fps. It changes the rate only; it does not deinterlace the video or remove 3:2 pulldown.
How much will the file size change going from WebM to MKV?
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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 WebM 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.
Will the MKV file play on iPhone, Android, and Smart TVs?
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MP4 with H.264 plays on practically every phone, browser and TV. MOV with H.264 plays on Apple devices and most TVs but not on every older Android phone. MKV needs an app such as VLC on iOS, and WebM is at home in browsers. There is no device preset on this page, so choose the target format your device supports.
How long does converting a 1-hour WebM video to MKV take?
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There is no fixed time: it depends on the length, the resolution and the target format. Conversions run on our servers' CPUs with software encoders; there is no GPU acceleration. MKV to MP4 or MOV with the default settings copies the video stream and is the quickest. A re-encode to H.264 takes longer, and WebM (VP9) is the slowest target, several times slower than H.264 in our tests.
