Step 1: Transfer your MKV files using the button above or by slide and deposit.
Step 2: Click the 'Convert' button to start the conversion.
Step 3: Retrieve your converted WebM files.
MKV to WebM Conversion FAQ
How do I re-encode MKV to WebM without losing video quality?
+
Upload your MKV file and the converter runs a CRF-based re-encode targeting visually-lossless WebM output (CRF 18 by default, lower values = larger file / higher quality). The codec is chosen to match the WebM container — H.264 for broad-compat MP4, H.265 for size-efficient MKV, VP9 for WebM, AV1 for newer pipelines. 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. WebM is deliberately narrow: VP8 or VP9 video (AV1 more recently) with Vorbis or Opus audio, and nothing else.
Can MKV be converted to WebM without re-encoding the video?
+
Yes, and it is the fast path. MKV and WebM share the same underlying box structure, so the video and audio streams are copied across byte-for-byte and only the container wrapper is rewritten. Nothing is decoded and nothing is re-compressed, so a feature-length file finishes in under a minute instead of half an hour, with output quality identical to the source. MKV is Matroska, an open container designed in 2002 with no licensing restrictions and no ceiling on what it can hold. WebM is a strict subset of Matroska that Google published in 2010 specifically to give HTML5 video a royalty-free container.
My MKV has several audio tracks — do they all survive into the WebM?
+
Not dependably. MKV stores multiple audio streams as first-class tracks, but WebM playback support past the first track is inconsistent, so most players will only ever expose one. Choose the track you actually want before converting; the others are better extracted to their own files than left in a container that hides them. MKV is the archival container of choice because it stores unlimited audio tracks, soft subtitles, chapter markers and cover art in one file. WebM is a poor fit anywhere outside a browser — video editors, phones’ native galleries and Smart TVs largely ignore it.
Will the WebM play in a browser when the MKV would not?
+
Yes, and that is usually the whole reason for the conversion. An MKV embedded in a web page either shows a broken player or forces a download, because browsers ship no decoder for it. WebM plays inline through the native HTML5 video element with no plugin and no external application. 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.
Which video codec does the WebM output use?
+
It depends on the WebM container. MP4 defaults to H.264 for the broadest playback support across phones, browsers, and Smart TVs. MKV defaults to H.265 / HEVC for roughly half the file size at equivalent quality. WebM defaults to VP9. The advanced options expose explicit codec choice if you need to override.
Will my audio track survive MKV to WebM conversion?
+
Yes. When MKV and WebM share an audio codec (e.g. both carry AAC), audio is re-muxed with no re-encode — bit-identical. When the codecs differ, audio is transcoded to AAC / Opus / Vorbis depending on what the WebM container supports. Multi-track audio (commentary, alternate languages) is preserved.
Can I keep the original framerate when converting MKV to WebM?
+
By default yes — a 24fps MKV stays 24fps in WebM; a 60fps MKV stays 60fps. If you need to change rate (e.g. interlaced 29.97 → progressive 30, or 60 → 30 for upload limits), the framerate option handles 3:2 pulldown, deinterlacing, and frame-blending in the same encode pass.
How much will the file size change going from MKV to WebM?
+
Same-codec re-mux (MKV H.264 → WebM H.264 just changing container): nearly identical size. Codec change can swing dramatically: H.264 → H.265 typically halves the file at the same visual quality; VP9 is roughly comparable; AV1 cuts another 20-30% but is slower to encode.
Will the WebM file play on iPhone, Android, and Smart TVs?
+
MP4 / H.264 plays natively on every modern device. MOV / H.264 plays on Apple devices and most TVs but not always on older Android. MKV needs VLC on iOS. WebM is browser-first. The advanced options include a "device compatibility" preset that picks the safest WebM codec / container for your target.
How long does converting a 1-hour MKV video to WebM take?
+
Same-codec re-mux is near-instant — 30 to 60 seconds for a 1-hour file. A full codec re-encode runs at roughly 0.3-0.7x source duration on our GPU pipeline, so a 1-hour MKV → WebM finishes in 18-40 minutes depending on resolution and target codec.
What is the maximum resolution supported for MKV to WebM?
+
Up to 8K (7680×4320) on Premium plans. Free conversions are capped at 4K (3840×2160) by the per-file size limit. HDR metadata (HDR10, HDR10+, Dolby Vision when present) is carried through where both MKV and WebM containers support it.
Is my MKV video private during conversion to WebM?
+
Yes. Uploaded video files are processed in isolated workers, never viewed by a human, never indexed, and deleted within minutes of completion. The retention window is documented at /privacy/ and we publish no training corpus from user uploads.
