Matroska supports storage of related files and data in the Attachments Element (a Top-Level Element). Attachment Elements can be used to store related cover art, font files, transcripts, reports, error recovery files, picture or text-based annotations, copies of specifications, or other ancillary files related to the Segment.
Matroska Readers MUST NOT execute files stored as Attachment Elements.
This section defines a set of guidelines for the storage of cover art in Matroska files. A Matroska Reader MAY use embedded cover art to display a representational still-image depiction of the multimedia contents of the Matroska file.
Only JPEG and PNG image formats SHOULD be used for cover art pictures.
There can be two different covers for a movie/album: a portrait style (e.g., a DVD case) and a landscape style (e.g., a wide banner ad).
There can be two versions of the same cover, the normal cover and the small cover. The dimension of the normal cover SHOULD be 600 pixels on the smallest side (for example, 960x600 for landscape, 600x800 for portrait, or 600x600 for square). The dimension of the small cover SHOULD be 120 pixels on the smallest side (for example, 192x120 or 120x160).
Versions of cover art can be differentiated by the filename, which is stored in the FileName Element. The default filename of the normal cover in square or portrait mode is cover.(jpg|png). When stored, the normal cover SHOULD be the first Attachment in storage order. The small cover SHOULD be prefixed with "small_", such as small_cover.(jpg|png). The landscape variant SHOULD be suffixed with "_land", such as cover_land.(jpg|png). The filenames are case sensitive.
The following table provides examples of file names for cover art in Attachments.
| FileName | Image Orientation | Pixel Length of Smallest Side |
|---|---|---|
| cover.jpg | Portrait or square | 600 |
| small_cover.png | Portrait or square | 120 |
| cover_land.png | Landscape | 600 |
| small_cover_land.jpg | Landscape | 120 |