Body: <p>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 <code>cover.jpg</code>.  </p>
  
  <p>From the name <code>cover.jpg</code> 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? </p>
  
  <p>The files have one <code>normal</code> video stream, maybe multiple audio streams, and about 4 mjpeg streams.</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-06-27T01:14:16.267Z
Comments.Text: Post the command you used.
Comments.UserDisplayName: stib
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-06-28T19:59:04.447Z
Comments.Text: It is in the video file, I didn't add it there. I don't understand the use case of it
Comments.UserDisplayName: Ronon
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-06-29T10:51:23.100Z
Comments.Text: 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.
Comments.UserDisplayName: stib
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-07-01T22:59:28.770Z
Comments.Text: 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
Comments.UserDisplayName: Ronon
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-07-02T01:31:43.923Z
Comments.Text: Kodi and other media centres use cover.jpg to show the poster image in their menus. Where did the videos come from? https://www.matroska.org/technical/cover_art/index.html
Comments.UserDisplayName: stib
Tags: <video><mkv>
Title: Mjpeg in video containers use case
UserDisplayName: Ronon
ThreadText: # Mjpeg in video containers use case
  
  (Asked by: username_0 on 2019-06-24)
  
  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.
  
  **Tags:** video, mkv
  
  > **Comments:**
  > **username_1**: Post the command you used.  
  > **username_0**: It is in the video file, I didn't add it there. I don't understand the use case of it  
  > **username_1**: 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.  
  > **username_0**: 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  
  > **username_1**: Kodi and other media centres use cover.jpg to show the poster image in their menus. Where did the videos come from? https://www.matroska.org/technical/cover_art/index.html  
  
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  ## 0 answers
  
  