Slower, but the result plays on practically every device.
Updated July 2026
About this tool
MKV is the Matroska container — a favorite of screen recorders like OBS and of high-quality rips, because it can hold practically anything: multiple audio tracks, subtitle streams, chapters and any codec. The catch is playback: many TVs, phones and web players never shipped a Matroska demuxer, even when they support the H.264 or HEVC video inside.
This converter is remux-first: when your MKV carries MP4-compatible streams, they are remuxed — moved into an MP4 container without re-encoding — so the video stays bit-identical to the original; only incompatible streams are transcoded. Audio that MP4 players don't handle, such as AC-3 or E-AC-3, is converted to AAC where your browser can decode it (typically Safari and Edge); audio your browser can't decode — DTS, or AC-3 in Chrome and Firefox — is dropped with a notice while the video still converts. The output keeps the video and the default audio track — text subtitles MP4 cannot carry are dropped, not burned in.
Conversion runs in a Web Worker in your browser — videos are never uploaded.
Frequently asked questions
Is MKV to MP4 conversion lossless?
Usually, yes. MKV and MP4 are containers; when yours holds MP4-compatible streams (H.264/HEVC video, AAC audio), they are remuxed — repackaged without re-encoding — so the video is bit-identical. Incompatible audio like AC-3 or E-AC-3 is converted to AAC where your browser can decode it (typically Safari and Edge); audio it cannot decode — DTS, or AC-3 in Chrome and Firefox — is dropped with a notice. The video stream still passes through untouched.
What happens to subtitles and extra audio tracks?
MKV can hold many audio and subtitle tracks; MP4 supports far fewer subtitle formats. The tool keeps the video and the default audio track; text subtitles that MP4 cannot carry are dropped, not burned in. If you need a specific language, check which track is set as default before converting.
Are my files uploaded anywhere?
No. The conversion runs locally in your browser using its built-in codecs (WebCodecs) — your movies and recordings never leave your device. There is also no file-size cap imposed by a server; very large files are limited only by your device's memory.
Why won't my TV or phone play MKV files?
Many TVs, phones and web players simply don't include a Matroska demuxer, even when they support the codecs inside. MP4 with H.264/AAC is the de-facto universal profile, so remuxing MKV to MP4 keeps the exact same picture in a wrapper every device understands.