Restrictions on adaptation sets

There are several restrictions on adaptation sets.

For the set of representations in an adaptation set in an HbbTV profile-specific MPD:

  • Each representation contains only one media component: a single audio or video track. Other nonmedia components may be present if applicable.
  • All representations have the same track_ID in the track header box and track fragment header box.
  • The initialization segment is common for all representations. Additionally, all information necessary to decode any segment chosen from representations is provided in the initialization segment.

    A common initialization segment means that all representations in an adaptation set have the same stsd box. There is one entry in the stsd box for each representation. Representations encoded with different parameters (for example, at different bit rates) use the same sample_description_index in the track fragment header to identify which one of the sample entries in the stsd box is applicable to them. Each segment consists of a whole self-contained movie fragment.

  • Segments are at least one second long, except for the last segment in an MPD, which may be shorter.
  • Each audio segment has a duration of no more than 15 seconds. (Video segments have the same requirement.)

For a detailed list of nonaudio MPD requirements, including requirements for transitions between representations, see ETSI TS 102 796.