Implementation Recommendations

Cluster

It is RECOMMENDED that the size of each individual Cluster Element be limited to store no more than 5 seconds or 5 megabytes.

SeekHead

It is RECOMMENDED that the first SeekHead Element be followed by a Void Element to allow for the SeekHead Element to be expanded to cover new Top-Level Elements that could be added to the Matroska file, such as Tags, Chapters, and Attachments Elements.

The size of this Void Element should be adjusted depending whether the Matroska file already has Tags, Chapters, and Attachments Elements.

Optimum Layouts

While there can be Top-Level Elements in any order, some ordering of Elements are better than others. Here are few optimum layouts for different use case:

Optimum layout for a muxer

This is the basic layout muxers should be using for an efficient playback experience.

• SeekHead
• Info
• Tracks
• Chapters
• Attachments
• Tags
• Clusters
• Cues

Optimum layout after editing tags

When tags from the previous layout need to be extended, they are moved to the end with the extra information. The location where the old tags were located is voided.

• SeekHead
• Info
• Tracks
• Chapters
• Attachments
• Void
• Clusters
• Cues
• Tags

Optimum layout with Cues at the front

Cues are usually a big chunk of data referencing a lot of locations in the file. For players that want to seek in the file they need to seek to the end of the file to access these locations. It is often better if they are placed early in the file. On the other hand that means players that don’t intend to seek will have to read/skip these data no matter what.

Because the Cues reference locations further in the file, it’s often complicated to allocate the proper space for that element before all the locations are known. Therefore shis layout is rarely used.

• SeekHead
• Info
• Tracks
• Chapters
• Attachments
• Tags
• Cues
• Clusters

Optimum layout for livestreaming

In Livestreaming ((#livestreaming)) only a few elements make sense. SeekHead and Cues are useless for example. All elements other than the Clusters MUST be placed before the Clusters.

• Info
• Tracks
• Attachments (rare)
• Tags
• Clusters