MKV file has no sound on Xbox One

This means that VLC doesn't recognize the format of one of the data streams in your MKV file. It can't play this file and considers it unfixable.

Without more details, we can't tell you why VLC thinks the file is broken. You can try:

• playing it in another media player;
• updating to a later (or earlier) version of VLC and trying again;
• re-encoding the file (if you encoded the MKV yourself), possibly using different settings or a different encoder; or
• downloading the file again (if you downloaded it from the Internet).

You might look into MKVtoolnix (for Linux, OSX, Cygwin and Windows) or MKVtools (for OSX). MKVtoolnix is a set of tools for creating, altering, and inspecting MKV files; your MKV may be reparable using them. Start with the following command, and inspect the output for errors; it may give you more information about what's wrong with the file:

mkvinfo filename.mkv

mkvtomp4

Looks like mkvtomp4 is what you want?

Uses mpeg4ip or GPAC's MP4Box, mkvtoolnix and ffmpeg to convert troublesome mkv files to mp4. The conversion does not re-encode the video and only re-encodes the audio if it doesn't use AAC codec (one can override this behaviour using --audio-codec).

You can download Windows and Linux versions on the Google Code page. You will need additional software though.

• mkvtoolnix
• MP4Box

Check the sites for downloads for either Windows or Linux. On OS X, you only need to brew install mkvtoolnix mp4box if you have Homebrew.

This will not copy your subtitles though. You'll need an additional step.

FFmpeg batch

If mkvtomp4 does not work for you, a simple FFmpeg batch file could also do.

Install ffmpeg (e.g. via Homebrew or options from https://ffmpeg.org/download.html). Then, just call:

ffmpeg -i input.mkv -c:v copy -c:a copy output.mp4

This will create a valid MP4 container without re-encoding. Loop over the files as needed and available by your operating system. This batch won't, however, copy subtitles.

In *nix, you could do the following. Just create a file convert.sh:

#!/bin/bash
find /path/to/input/folder -iname '*.mkv' -print0 | while read -d '' -r file; do
    ffmpeg -i "$file" -c:v copy -c:a copy ${file%%.mkv}.mp4
done

Replace the path to your video folder here. Make it executable with chmod +x convert.sh, then run it with ./convert.sh.

In Windows, you probably need two Batch files (shameless plug from here), one being startconvert.bat:

for %%i IN (*.mkv) DO (convert-to-mp4.bat "%%i") 
pause

And one that performs the conversion:

IF EXIST "%1.mp4" GOTO exit

@echo Conversion for %1 started on %DATE% %TIME% 
ffmpeg -i %1 -c:v copy -c:a copy %1.mp4

:exit 
@echo %1.mp4 already exists

Save both in the video folder. Simply run startconvert.bat from the folder you want to start the conversion from.

Subtitles

If you want to add the subtitles, you might need a manual procedure if the following doesn't work for you:

ffmpeg -i input.mkv -c:a copy -c:v copy -map 0 output.mp4

To extract subtitles, use:

mkvextract tracks input.mkv 3:subtitles.srt

This is assuming that your file really contains the subtitles at track ID number 3 and they can be exported to the SRT format. To check whether a file really contains subtitles at track 3, use mkvmerge -i input.mkv.

Then, use MP4Box to re-add the subtitles to the MP4 file.

mp4box -add input.mp4 -add subtitles.srt -new output.mp4