What’s the best format for uploading videos to the web?

MP4 with H.264 video and AAC audio: it plays in every browser and device.

Does Dembed accept MKV?

Yes, but we warn you on upload: if the audio is AC-3 or DTS it won’t be heard in browsers. To avoid that, upload MP4 (H.264 + AAC).

How to convert MKV to MP4 without losing quality, with sound

Updated: October 28, 2026

It’s a very common problem: you upload an MKV, the picture is perfect, but there’s no sound. The file isn’t broken: browsers can’t play certain audio formats often found inside MKVs. The fix is converting it to MP4 with AAC audio, which you can do for free, in minutes, without losing picture quality.

Why an MKV plays without sound in the browser

MKV is a “container”: it holds a video track, one or more audio tracks and sometimes subtitles. Many MKVs carry audio in AC-3 (Dolby Digital), E-AC-3, DTS or TrueHD, formats that Chrome, Firefox and Safari don’t decode.

The browser plays the picture and skips the audio. That’s why the same file has sound in VLC or on your TV, but not on a website.

Option 1: HandBrake (free, with a GUI)

1Download HandBrake from its official site (Windows, macOS and Linux) and open your MKV.
2Pick the “Fast 1080p30” preset (or the one matching your video’s resolution).
3Under “Summary”, format: MP4 and tick “Web Optimized”.
4Under “Audio”, codec AAC (avcodec), 160–192 kbps.
5Click “Start Encode”. When it’s done, upload the MP4.

Option 2: ffmpeg (fast, no picture re-encode)

If the video is already H.264, this command copies the picture as-is (lossless, in seconds) and only converts the audio to AAC:

ffmpeg -i input.mkv -map 0:v:0 -map 0:a:0 -c:v copy -c:a aac -b:a 192k -movflags +faststart output.mp4

If the video is HEVC (H.265) or the MP4 won’t play

Some browsers don’t play H.265. In that case re-encode the picture to H.264 too (it takes longer):

ffmpeg -i input.mkv -map 0:v:0 -map 0:a:0 -c:v libx264 -crf 20 -preset medium -c:a aac -b:a 192k -movflags +faststart output.mp4

Extract the MKV’s subtitles

If the MKV has text subtitles, export them to an .srt and upload them separately on Dembed (you can add several languages per video):

ffmpeg -i input.mkv -map 0:s:0 subtitles.srt

Frequently asked questions

With ffmpeg and “-c:v copy”, no: the picture is copied as-is. HandBrake re-encodes, but with the right preset the difference isn’t noticeable.