Created attachment 221964 [details]
Test file

I've attached a test file (simple mpeg video and LOTS of Matroska tags). When gst-discoverer is run on it, the result is:

Topology:
  container: video/x-matroska
    video: video/mpeg, systemstream=(boolean)false, mpegversion=(int)1, width=(int)320, height=(int)200, pixel-aspect-ratio=(fraction)1/1, framerate=(fraction)48000/1001, interlace-mode=(string)mixed
      Codec:
        video/mpeg, systemstream=(boolean)false, mpegversion=(int)1, width=(int)320, height=(int)200, pixel-aspect-ratio=(fraction)1/1, framerate=(fraction)48000/1001, interlace-mode=(string)mixed
      Additional info:
        None
      Width: 320
      Height: 200
      Depth: 0
      Frame rate: 48000/1001
      Pixel aspect ratio: 1/1
      Interlaced: true
      Bitrate: 0
      Max bitrate: 0
      Tags:
        None
      
      video: video/mpeg, systemstream=(boolean)false, mpegversion=(int)1, width=(int)320, height=(int)200, pixel-aspect-ratio=(fraction)1/1, framerate=(fraction)24000/1001, interlace-mode=(string)mixed, parsed=(boolean)true, codec_data=(buffer)000001b31400c811ffffe0a4
        Codec:
          video/mpeg, systemstream=(boolean)false, mpegversion=(int)1, width=(int)320, height=(int)200, pixel-aspect-ratio=(fraction)1/1, framerate=(fraction)24000/1001, interlace-mode=(string)mixed, parsed=(boolean)true, codec_data=(buffer)000001b31400c811ffffe0a4
        Additional info:
          None
        Width: 320
        Height: 200
        Depth: 0
        Frame rate: 24000/1001
        Pixel aspect ratio: 1/1
        Interlaced: false
        Bitrate: 0
        Max bitrate: 0
        Tags:
          taglist, title=(string){ filesegmenttitle, ALBUM/TITLE, TITLE }, artist=(string){ ALBUM/ARTIST, ARTIST }, copyright=(string)COPYRIGHT, composer=(string)COMPOSER, genre=(string)GENRE, encoder=(string)ENCODER, isrc=(string)ISRC, license=(string)TERMS_OF_USE, image=(GstSample)NULL, container-format=(string)Matroska, video-codec=(string)"MPEG\ 1\ Video", language-code=(string)de;
        

Properties:
  Duration: 0:00:04.171000000
  Seekable: yes
  Tags: 
      title: filesegmenttitle, ALBUM/TITLE, TITLE
      artist: ALBUM/ARTIST, ARTIST
      copyright: COPYRIGHT
      composer: COMPOSER
      genre: GENRE
      encoder: ENCODER
      ISRC: ISRC
      license: TERMS_OF_USE
      image: (null)
      container format: Matroska
      video codec: MPEG 1 Video
      language code: de


What's wrong with it:
1) Nested video streams with different framerate.
2) Matroska parser does not understand the concept of tags that depend on context (i.e. TargetType), and thus can't tell a difference between album title and track title. Same goes for track number.
3) Matroska parser simply misses some tags. ENCODED_BY, for example. Even if some tags were unknown, parser should have used EXTENDED_COMMENT tag type to present them as key=value pairs.