Converts WebM files to MKV format — web-optimized video to advanced video archiving with multiple subtitle tracks, chapters, and audio streams in one file. All conversion happens locally in your browser with no file size limits.
Runs on FFmpeg
Content reviewed October 2026 · About Toolzum
Convert MKV video files to WEBM format directly in your browser. 100% free, private — your files never leave your device.
Convert WEBM video files to AVI format directly in your browser. 100% free, private — your files never leave your device.
Convert AVI video files to MKV format directly in your browser. 100% free, private — your files never leave your device.
Convert MKV video files to MP4 format directly in your browser. 100% free, private — your files never leave your device.
Convert MOV video files to MKV format directly in your browser. 100% free, private — your files never leave your device.
WebM (WebM Video) uses lossy compressed encoding and is best for web-optimized video — streaming, embedded players, and HTML5 video tags with fast loading. MKV (Matroska Video) uses lossless container encoding and excels at advanced video archiving with multiple subtitle tracks, chapters, and audio streams in one file. Converting between them lets you take advantage of each format's strengths — for example, using a compressed format for sharing and a lossless format for editing. All conversion happens locally in your browser with no file size limits.
Convert WEBM video files to MKV format directly in your browser. 100% free, private — your files never leave your device.
From lossy compressed to lossless container: quality is preserved as far as the formats allow.
Yes — archive WebM originals before batch-converting. Re-converting from MKV back to WebM never restores discarded data.
Seconds for typical files on a modern device; large files scale with size and CPU. Conversion speed depends on the machine, not the formats — close heavy tabs for big batches.
Video to MP3 Converter
Extracts the audio track from uploaded video files (MP4, MOV, AVI, WebM) and encodes it as a high-quality MP3 file. Free to start with no signup.
Crop Video
Crop the visual area of your MP4 or WebM video directly in the browser with 9:16, 1:1, 16:9 presets or custom dimensions with X/Y offsets. Free to start with no signup.
Video Compressor
Reduces MP4, MOV, and WebM video file sizes with a configurable CRF 20–40 slider (default 28, libx264 fast preset), plus a GIF mode with color-palette control. Videos never leave your device — compression runs locally in your browser with FFmpeg WASM.
Video to GIF
Convert MP4/WebM to GIF animations. Videos up to 250MB. Videos never leave your device — compression and conversion run locally in your browser with FFmpeg WASM.
Subtitle Translator
Translate pasted SRT or VTT subtitle text into 9 languages (Spanish, French, German, Japanese, Chinese, Hindi, Portuguese, Russian, Arabic) while preserving every timestamp — AI-powered with your own API key, text never stored.
Video Watermark Adder
Burn text watermarks into a video with 5 position presets (bottom-right default, fixed 24px white on semi-transparent black box). Brand one clip at a time — local FFmpeg work, unlimited saves.