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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.

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  • 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

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