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WEBM
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MKV

WebM to MKV Converter — Free, Online, No Upload

MKV and WebM share codecs — remux your WebM into MKV for full Plex and Jellyfin compatibility without re-encoding.

Free · no signup2 free files a day100% in-browser · no upload

Tap to select WEBM files

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2 free files per day (2 left today) · Up to 10 MB each · Upgrade for more

✓ Files never uploaded✓ 100% browser-based✓ No account required
Need the reverse?MKV → WEBM

How to convert WEBM to MKV online

  1. 1

    Drop your WEBM file

    Drag your WebM Video Format file onto the box above, or click it to pick a file.

  2. 2

    Wait a few seconds

    Conversion starts on its own and runs on your device, not on a server.

  3. 3

    Download your MKV

    Click Download to save the Matroska Video file.

WEBM vs MKV: format overview

WEBM

WebM Video Format

Google (On2 Technologies) · 2010

Compression
lossy
Transparency
No
  • ✓ Royalty-free codec (VP8/VP9/AV1)
  • ✓ Excellent web streaming support
  • ✗ Not supported on iOS/Safari natively
MKV

Matroska Video

Matroska.org · 2002

Compression
lossy
Transparency
No
  • ✓ Supports virtually any codec combination
  • ✓ Multiple audio tracks and subtitles per file

WEBM magic bytes: 1A 45 DF A3

MKV magic bytes: 1A 45 DF A3

Why convert WEBM to MKV?

You have a WebM video from a web download, screen recorder, or browser-based tool, and you want to organize it in your Plex, Jellyfin, or Kodi media library. WebM is a web streaming format — Plex and Jellyfin treat it differently from library files, and some client devices and TV apps handle WebM inconsistently. MKV is the standard container for home media servers, with mature, reliable support across all Plex and Jellyfin clients.

MKV and WebM share codecs: VP9 video and Opus audio are native to both the WebM and MKV container formats. When your WebM already uses these codecs — the typical case for browser recordings and web downloads — conversion to MKV is a remux: the video and audio streams are moved to the new container without any re-encoding. This means zero quality loss and very fast processing, regardless of file size.

The practical result is that your video appears in Plex and Jellyfin as a proper MKV library file, with correct metadata matching, reliable thumbnail generation, and consistent playback across all client types including smart TVs, Roku, Fire TV, and Apple TV apps. MKV also supports richer metadata, embedded subtitles (SRT, ASS), and multiple audio tracks — features that WebM handles more awkwardly.

Quality & file size: WEBM to MKV

Typical sizes (1 minute 1080p): WEBM 50–200 MB → MKV 200–800 MB.

Frequently asked questions

Is WebM to MKV just a container change?
Often yes — WebM uses VP8/VP9 video and Opus audio, both of which are natively supported in MKV. In that case, conversion is a remux: no re-encoding, no quality loss.
Why does Plex sometimes prefer MKV over WebM?
Plex's media library management and metadata matching is optimised for MKV. WebM is treated as a web streaming format rather than a library file, and some Plex clients handle MKV more reliably.

Your WEBM file never leaves this tab — FormatDrop has no endpoint that receives file data. How it works