MKV to MP4 Converter
Turn MKV into MP4 that TVs and phones play — with your choice of audio and subtitles.
What will happen
Subtitle files
About the MKV to MP4 Converter
MKV (Matroska) can hold almost any codec plus several audio and subtitle tracks, but many TVs, phones, editors and websites only accept MP4. When the video is H.264, HEVC, AV1 or VP9 and the audio is AAC, MP3, Opus or Dolby Digital (AC-3/E-AC-3), this page moves the tracks into an MP4 without re-encoding: it is fast, even for long films, and the picture and sound are untouched.
Audio that MP4 players handle poorly — DTS, FLAC, Vorbis and PCM — is converted to stereo AAC, and you can convert Dolby tracks too for devices without Dolby support. You choose which audio languages to keep, and text subtitles (SRT, SSA/ASS, WebVTT) can be saved as separate .srt files and/or added to the MP4 as WebVTT tracks. Before anything runs, the page lists what happens to every track. Nothing is uploaded.
How to use it
- Drop the .mkv file on the box, or click Choose an MKV file. The page lists every video, audio and subtitle track it contains.
- Under Audio tracks, untick languages you do not need. Tick Convert Dolby audio to AAC if your TV or phone has no Dolby support.
- Under Subtitles, choose the tracks to keep and whether to save them as .srt files, put them inside the MP4 (WebVTT) or both. To get only the subtitles, press Download only the subtitles.
- Check What will happen, press Convert to MP4, then download the MP4 and any subtitle files.
Examples
movie.mkv · HEVC · AAC (English) + AC-3 5.1 (Hindi) · SRT (English)
movie.mp4 with HEVC and both audio tracks copied, plus movie.eng.srt.
concert.mkv · H.264 · DTS 5.1
concert.mp4 — video copied, DTS converted to stereo AAC.
DTS is decoded by a decoder built into the page, so this works in every supported browser.
episode.mkv · H.264 · Opus · ASS subtitles
episode.mp4 and episode.jpn.srt (or eng/spa…) with the dialogue text; ASS styling and positioning are not kept.
What MP4 can and cannot hold
- Copied as they are: H.264, HEVC, AV1 and VP9 video; AAC, MP3, Opus, AC-3 and E-AC-3 audio.
- Converted to AAC: DTS, FLAC, Vorbis and PCM audio (mixed to stereo when they have more channels).
- Converted to H.264: VP8 video. Older codecs such as MPEG-2, MPEG-4 Part 2 (DivX/Xvid) or VC-1 cannot be decoded in the browser, so such files cannot be converted here.
- Left out: Dolby TrueHD (browsers cannot decode it), attachments such as fonts, and chapters.
Subtitles: .srt files or a track inside the MP4?
Separate .srt files work almost everywhere: TVs, VLC, Plex, YouTube uploads and most players load a file named like the video (for example movie.eng.srt next to movie.mp4). WebVTT tracks inside the MP4 keep everything in one file and are read by VLC and web players, but FFmpeg-based tools and many TVs and phones do not show them. When in doubt, choose both. SSA/ASS subtitles are converted to plain text with italic, bold and underline kept; their fonts, colours and positions are not. Image-based subtitles (Blu-ray PGS, DVD VobSub) cannot be turned into text without OCR, so they are listed but not converted.
Why keep only some audio tracks?
Every extra audio track adds to the file size: a Dolby Digital 5.1 track at 384–640 kbps is about 0.35–0.6 GB for a two-hour film. Removing languages you will not use makes the MP4 smaller without touching the video.
Limitations
- Converting DTS, FLAC, Vorbis or PCM produces stereo AAC; surround channels are mixed down. Copied tracks (AC-3, E-AC-3, AAC) keep their channels.
- Chapters, attachments (fonts, cover images) and image-based subtitles are not carried over.
- Video that is not H.264, HEVC, AV1, VP9 or VP8 cannot be converted in the browser.
- Reading subtitles means scanning the whole file, which takes a few seconds for multi-gigabyte films.
- Without “Save straight to a file” (Chrome/Edge on a computer) the MP4 is held in memory until you download it, so very large files can fail on phones.
Privacy
Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.
Frequently asked questions
Does converting MKV to MP4 reduce quality?
No — the video, and audio that MP4 supports, are copied without re-encoding. Only DTS, FLAC, Vorbis, PCM (and Dolby, if you choose) are re-encoded to AAC.
Why is my TV not showing the subtitles?
Many TVs ignore subtitle tracks inside MP4. Put the .srt file next to the MP4 with the same name (for example movie.eng.srt), or burn the subtitles into the video with a desktop editor.
Are my files uploaded?
No. The MKV is read and converted inside your browser; the MP4 and subtitle files are created on your device.
Can I extract only the subtitles?
Yes. Load the MKV, tick the subtitle tracks you want and press Download only the subtitles — the .srt files (several come as one ZIP) are saved straight away, with the MKV’s own timing, and nothing is converted.
What happens to Dolby Atmos or TrueHD audio?
Dolby TrueHD cannot be decoded in the browser, so those tracks are left out and the page tells you. Dolby Digital (AC-3) and Dolby Digital Plus (E-AC-3) tracks are copied unchanged unless you choose to convert them to AAC.