Preview of MKV files should show attached image first

[MiMoHo]

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When a custom icon or image attachment is included with a MKV file, QLVideo should show this thumbnail as the first big preview frame as long as true QuickLook playback of MKV videos is not supported what would make this plug-in outstanding.

[Kagami]

Not sure if that was fixed but it seems to be working now:

  Stream #0:4: Video: png, rgba(pc), 504x625 [SAR 3780:3780 DAR 504:625], 90k tbr, 90k tbn (attached pic)
    Metadata:
      filename        : cover.png
      mimetype        : image/png

  Stream #0:3: Video: png, rgba(pc), 500x620 [SAR 3780:3780 DAR 25:31], 90k tbr, 90k tbn (attached pic)
    Metadata:
      filename        : cover.png
      mimetype        : image/png