From time to time i'm converting mkv to mp4 using ffmpeg in order to save disk space. Currently i noticed that in some files multiple mjpeg streams where also included. Some of them were named cover.jpg.

From the name cover.jpg i assume that it is supposed to be displayed in some cases?!? But i never heard or saw that any program, eg. vlc, used an image to display anything from the video. So what is the use case of including pictures in a video file?

The files have one normal video stream, maybe multiple audio streams, and about 4 mjpeg streams.

  • Post the command you used.
    – stib
    Jun 27, 2019 at 1:14
  • It is in the video file, I didn't add it there. I don't understand the use case of it
    – Ronon
    Jun 28, 2019 at 19:59
  • mkv, like mp4 is a container format that is able to contain many different streams, including video, audio, subtitles, metadata and images. I'd guess that cover.jpg contains a poster image for displaying on a media playback system. BTW it's not the container format that dictates the size of the file. Mp4 isn't any more space efficient than mkv.
    – stib
    Jun 29, 2019 at 10:51
  • Never saw the cover.jpg in action on any kind of player. MP4 ist web playable, thats why I use this format instead of keeping it as mkv
    – Ronon
    Jul 1, 2019 at 22:59
  • Kodi and other media centres use cover.jpg to show the poster image in their menus. Where did the videos come from? matroska.org/technical/cover_art/index.html
    – stib
    Jul 2, 2019 at 1:31


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.