Convert WebM to MKV — Free Online Converter
Convert WebM Video (.webm) to Matroska Video (.mkv) online for free. Fast, secure video conversion with no watermarks or registration....
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Sådan konverterer du
Upload your .webm file by dragging it into the upload area or clicking to browse.
Choose your output settings. The default settings work great for most files.
Click Convert and download your .mkv file when it's ready.
About WebM to MKV Conversion
WebM and MKV are closely related — WebM is a restricted subset of the Matroska (MKV) container format, limited to VP8/VP9/AV1 video with Vorbis/Opus audio. MKV supports any codec combination, including H.264, H.265, DTS, AC3, and unlimited subtitle tracks. Converting WebM to MKV lifts these restrictions while maintaining the Matroska container's capabilities.
Why Convert WebM to MKV?
MKV's broader codec support enables adding audio tracks in formats WebM does not support (AC3, DTS, FLAC), embedding subtitle tracks (SRT, ASS, PGS), and including chapter markers and attachments. For media server libraries (Plex, Kodi, Jellyfin), MKV provides better metadata handling and subtitle support than WebM.
The conversion can also re-encode VP9 to H.264/H.265 for broader device compatibility while staying in the Matroska container family.
Common Use Cases
- Adding SRT/ASS subtitle tracks to WebM video for multilingual media libraries
- Re-encoding VP9 WebM to H.264 MKV for broader player compatibility
- Embedding additional audio tracks (commentary, alternate language) into WebM content
- Adding chapter markers to WebM video for organized media library navigation
- Converting WebM for Plex/Kodi libraries that handle MKV metadata better
How It Works
For remuxing, FFmpeg copies VP8/VP9 video and Vorbis/Opus audio from WebM directly into MKV without re-encoding — since MKV is WebM's parent format, this is always lossless. For codec change, video is transcoded to H.264/H.265 and audio can remain or be converted. Additional tracks (subtitles, audio, attachments) are muxed in during conversion.
Quality & Performance
Remuxing is lossless — the bitstreams are identical. The MKV container adds no quality overhead. If re-encoding VP9 to H.264, typical CRF values produce comparable quality at similar file sizes.
Device Compatibility
| Device | WebM | MKV |
|---|---|---|
| Windows PC | Partial | Partial |
| macOS | Partial | Partial |
| iPhone/iPad | Partial | Partial |
| Android | Native | Partial |
| Linux | Partial | Partial |
| Web Browser | Native | No |
Recommended Settings by Platform
YouTube
Resolution: 1920x1080
Bitrate: 8-12 Mbps
H.264 recommended for fast processing
Resolution: 1080x1080
Bitrate: 3.5 Mbps
Square or 9:16 for Reels
TikTok
Resolution: 1080x1920
Bitrate: 4 Mbps
9:16 vertical, under 60s ideal
Twitter/X
Resolution: 1280x720
Bitrate: 5 Mbps
Under 140s, 512MB max
Resolution: 960x540
Bitrate: 2 Mbps
16MB limit for standard, 64MB for document
Discord
Resolution: 1280x720
Bitrate: 4 Mbps
8MB free, 50MB Nitro
Tips for Best Results
- 1Use remux (-c copy) when you just need MKV's extra features without re-encoding
- 2Add SRT subtitle tracks during the conversion for multilingual media library support
- 3Add chapter markers for structured content like tutorials, series, and lectures
- 4Re-encode VP9 to H.264 only when targeting players that cannot decode VP9
- 5Follow Plex/Kodi naming conventions for automatic metadata matching in media libraries
Related Conversions
WebM to MKV lifts codec restrictions from Google's web-focused container, enabling richer multimedia features while staying in the Matroska family.