MKV plays with no sound: why, and how to fix it
An MKV that shows picture but no sound usually has DTS or Dolby audio your TV, phone or player is not licensed to decode. Converting the sound to AAC fixes it.
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In short: When an MKV plays without sound, the audio track is almost always DTS, Dolby Digital (AC3) or Dolby TrueHD, which many TVs, phones and apps are not licensed to decode. Converting the file to MP4 rewrites the sound as AAC, which every device plays.
Why the picture works and the sound does not
An MKV is a container. The video inside is usually H.264 or H.265, which nearly everything decodes in hardware. The sound is often a surround format from a film release: DTS, AC3, E-AC3 or TrueHD. Decoding those requires a licence, and manufacturers of cheaper TVs, some phones and several apps do not pay for it. The player skips the track it cannot decode and carries on in silence.
How to check
Identify the file with the file inspector on this site, or open it in VLC and look at the codec information. If the audio says DTS, AC3, E-AC3 or TrueHD, that is the cause.
The fix
Convert the MKV to MP4. The sound is written as stereo AAC, which plays on every TV, phone and browser. The picture is re-encoded as H.264 at the same time, so the file plays everywhere rather than only where it did before.
If you only need the sound, for example to listen to a concert recording, Extract Audio writes it straight to MP3 or M4A.
If the MKV has several audio tracks
Films often carry two or three: the original language, a dub, a commentary. The conversion takes the first. It is usually the main one, but check the result before deleting the original.
Questions
Why does my TV play MKV video but no audio?
The audio is DTS or Dolby, which the TV is not licensed to decode. Converting to MP4 with AAC sound fixes it.
Does VLC play DTS?
Yes. VLC decodes DTS and AC3 itself, which is why a file can play in VLC and not on a TV.