Video to MKV - Online Video Format Converter — MKV (Matroska) is a flexible open container that holds virtually any video and audio codec, including the lossless FFV1 and FLAC streams, making it ideal for archival and high-fidelity editing workflows. Supports format conversion, lossless remuxing, compression, scaling, looping, and resizing — all processed locally in your browser, with files never uploaded to a server. A built-in metadata / tag editor reads the source video's tags (title, artist, album, album artist, date, genre, track, comment), lets you edit them, and writes them into the output — including the no-re-encode copy mode, where quality is perfectly preserved.
Supported input: Videos using open royalty-free codecs such as VP8/VP9/AV1/MPEG-4/FFV1 (WebM, MKV, MP4, MOV, AVI containers). Everything is converted locally in your browser; files are never uploaded to a server.
First use loads an ~30MB video processing engine into the current browser. It is cached and reused afterwards, so please be patient.
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Click to select or drag and drop a video file
Supports WebM, MKV, MP4, MOV, AVI and other common formats; under 500MB recommended
Quality:60higher = better quality, larger file; no effect with FFV1 (lossless)
Target bitrate:kbps; leave empty to decide automatically from the quality slider
Resolution:scaled automatically to preserve the original aspect ratio, no stretching
Loop count:the output video will play N times consecutively
Percent:100%scaled as a percentage of the original size
W×H:×fill in either value to scale proportionally; leave empty to use percent
Format Convert: Pick a codec combination and click the button below to remux/re-encode the video as MKV. MKV accepts nearly any codec, so "No re-encode" is available for most inputs for instant remuxing (no quality loss).
Video Compress: Re-encodes the video to MKV with the chosen quality or target bitrate to produce a smaller file. This mode requires re-encoding, so "No re-encode" is unavailable.
Video Scale: Scales the video to a preset resolution and outputs MKV. This mode requires re-encoding, so "No re-encode" is unavailable.
Video Loop: Repeats the video content N times and outputs MKV. Combined with "No re-encode" this completes almost instantly.
Video Resize: Scales the video by percentage or explicit width/height pixels and outputs MKV. This mode requires re-encoding, so "No re-encode" is unavailable.
Rewrites the metadata with a stream copy — video and audio are not re-encoded, so quality is perfectly preserved.
What is Matroska (MKV)? The container that holds everything
Matroska — named after the Russian nesting doll — is an open-standard container: it does not compress anything itself, it just nests any number of already-compressed streams inside one file. One MKV can hold a video track, several audio tracks (director's commentary, dubbing tracks), dozens of subtitle languages, chapter markers and even attachments — all in a format published under a free license with no patent claims. Where MP4 is a strict ISO standard with a narrow sanctioned codec list, Matroska's philosophy is "accept anything a player can play," which made it the archiving and anime/fan-subtitle community's favorite for two decades.
Five facts to anchor the rest of the page:
• MKV = container, not a codec — it stores streams, it never compresses them
• built on EBML, a binary XML: a parser reads the structure even when it meets unknown elements
• one file can carry multiple video/audio/subtitle tracks + chapters + attachments
• WebM is a Matroska profile: a WebM file is an MKV restricted to VP8/VP9/AV1 video and Vorbis/Opus audio
• moving a stream between MP4 and MKV is a remux — seconds, zero quality loss
EBML: self-describing like XML, compact like binary
Matroska's foundation is EBML (Extensible Binary Meta Language), a binary encoding of the idea behind XML: elements carry an ID, a length and a value, nested inside each other. Two properties follow. First, the file is streamable to parse — a player can walk the top-level structure without decoding any media. Second, it is forward-compatible — an element a parser has never seen before simply states its length and can be skipped whole, so old players still play new files. That resilience is why MKV files survive truncation and partial downloads far better than rigid formats.
Tracks, chapters and attachments
Each stream in an MKV is a track with its own codec ID, language tag and name ("Commentary", "Japanese with signs") — players offer them in a menu rather than making you swap files. Chapters are arbitrary timestamps with titles, exactly like DVD chapters. Attachments are arbitrary files embedded in the container, and their killer use is fonts: an ASS subtitle track that styles text in a specific typeface can ship the font itself inside the MKV, so the rendering is identical on every machine. None of this costs the video stream a single byte — the compressed frames are stored as-is.
MKV vs MP4
MP4 (ISO-BMFF) is the compatibility king: every phone, TV, browser and editor reads it. Matroska is the flexibility king: any codec combination, unlimited tracks, chapters, attachments, robustness. The two hold the same streams — an H.264 or VP9 stream sits identically in either box — so the choice is about features, not quality. Rule of thumb: distributing to unknown devices → MP4; archiving, multi-language, soft subtitles with fonts → MKV (or its WebM profile for the web).
Common misconceptions
"MKV is a codec / MKV is higher quality." It is a container. The same stream in MP4 and MKV is the same quality and virtually the same size; converting between them remuxes without touching the pixels.
"MKV files are huge." MKV adds only a thin structural overhead (kilobytes). Big MKVs are big because of the codecs and bitrates chosen, not the box.
"My device doesn't play MKV, so the file is broken." The player lacks the codec inside, or refuses the container by policy. Remux to MP4 with the same stream and it usually plays — proof the container was never the problem.
