.kara.json files


.kara.json files must all be created and filled automatically by this form in the system panel.

Karaoke Mugen data generation

In the case you modify media files or lyrics, you can update .kara.json files in several ways.

  • From a karaoke page in the system panel : drag and drop your new media or lyrics file in the form and save changes so karaoke Mugen will create a new .kara.json and replace the old one.
  • From the system panel : in the Database menu click on Validate
  • When Karaoke Mugen starts with the --validate option, the software will check if your files were changed. If they have changed, they will be updated and karaoke Mugen will exit.

Common issues

Video file can not be found despite being present

Verify on the FTP that the file is named exactly like in the .kara.json. Beware of case! Since Windows is case-insensitive, it won’t have any trouble, but for Linux where the lab is hosted, it will cause issues. Look carefully.

Another possibily is an invisible parasite character, a double space or something other from that. In doubt, copy-paste the file name from the .kara.json while renaming you media file

.ass lyrics files

Your subtitles are shifted/unsynced

Look up the time shifting section from the advanced guide



To encode videos, an array of tools exists.

  • Handbrake is the easiest to use, with a relatively correct user interface that is readable and somewhat good default options.
  • MediaCoder is a bit more shaky but is full of extra stuff: like the ability to keep some media tracks and re-encode other ones. Beware, it is a freemium: some options are only usable with the software’s full version.
  • MeGUI is a lot more harder to use but opitimizes encoding.
  • FFMPEG can be used in command line, making it very powerful but hard to master.
  • ShotCut allows to cut videos at the exact frame you want and uses FFMPEG, which makes your exports lighter.

Common issues

False metadata

In rare cases the “duration” can be wrong compared to reality. If it happens, it’s possible to get rid of the problem by recalibrating the video track and the incriminated audio in an MP4 container, using ffmpeg and the following command line (see the dedicated section)

“Crushed” lyrics on Karaoke Mugen

If you see that lyrics at the top of the screen seem to be crushed compared to other karaokes, or that letters are skipped, then the video has a bad ratio indicated in its metadata. See the capture below:

ass ass

You will have to re-encode the video with scale correction.

To find the values required for re-encoding, you will have to look in the mpv console, or use ffmpeg. For example, using mpv:

VO: [vdpau] 720x576 => 1024x576 vdpau[yuv420p]

Here, mpv indicates that the video is stretched in width, the width increases from 720 to 1024 pixels.

To fix the video, use ffmpeg and the following command, replacing the 1024:576 values with the values given by mpv.

./ffmpeg -i video_source.mp4 -c:a copy -c:v libx264 -vf "scale=1024:576" video_destination.mp4

For further explanation, see the dedicated section

Very big video files

Please use the tools and check rules on this page to produce light video files depending on their initial resolution. Sometimes re-encoding will be needed.

As a reminder, here are the expected video formats and the length/size ratio of videos:

  • Containers : MP4, MKV or WEBM
  • Video codecs : h264, h265, vp9 or AV1
  • Audio codecs : Opus, Vorbis, AAC or MP3

For more detail, see’s manifest which will always be up to date.

That table is indicative: for a given image resolution you should use the maximum Bitrate listed below to get an acceptable video size.

The karaoke base having a huge size already, it’s important to take as little space as possible. Having a 130Mb file for 1 minute 30 of video is not acceptable.

Video Resolution (Y axis) Maximum Birate Appromative file size, for 1 min 30
1080p 8000 kb/s 80Mb
720p 4000 kb/s 40Mb
480p 3000 kb/s 30Mb
360p 2000 kb/s 20Mb