Methods and apparatus for encoding and decoding overlay compositions

An apparatus configured to decode video data, the apparatus comprising a processor in communication with memory, the processor being configured to execute instructions stored in the memory that cause the processor to:

• receive multimedia data comprising a hierarchical track structure comprising at least a first track and a second track, wherein:
• the first track is at a first level in the hierarchical track structure and comprises first video media data;
• and
• the second track is at a second level in the hierarchical track structure above the first level of the first track and does not comprise any video media data;
• determine overlay composition metadata associated with the second track, wherein the overlay composition metadata comprises offset metadata, layer metadata, source metadata, or some combination thereof;
• and
• perform a track derivation operation on the first video media data associated with the first track, comprising performing, based on the overlay composition metadata, an overlay composition of the first video media data associated with the first track to generate second video media data of the second track such that the second track is a derived track of the first track.

A method for encoding video data, the method comprising:

• encoding a hierarchical track structure for multimedia data comprising at least a first track and a second track, wherein:
• the first track is at a first level in the hierarchical track structure and comprises first video media data;
• and
• the second track is at a second level in the hierarchical track structure above the first level of the first track and does not comprise any video media data;
• and
• encoding overlay composition metadata associated with the second track, wherein the overlay composition metadata comprises offset metadata, layer metadata, source metadata, or some combination thereof;
• wherein the overlay composition metadata specifies at least part of an overlay composition for the first video media data associated with the first track, wherein the overlay composition can be performed as part of a track derivation operation on the first video media data associated with the first track to generate second video media data of the second track, such that the second track is a derived track of the first track.

An apparatus for encoding video data, the apparatus comprising a processor in communication with memory, the processor being configured to execute instructions stored in the memory that cause the processor to:

• encode a hierarchical track structure for multimedia data comprising at least a first track and a second track, wherein:
• the first track is at a first level in the hierarchical track structure and comprises first video media data;
• and
• the second track is at a second level in the hierarchical track structure above the first level of the first track and does not comprise any video media data;
• and
• encode overlay composition metadata associated with the second track, wherein the overlay composition metadata comprises offset metadata, layer metadata, source metadata, or some combination thereof;
• wherein the overlay composition metadata specifies at least part of an overlay composition for the first video media data associated with the first track, wherein the overlay composition can be performed as part of a track derivation operation on the first video media data associated with the first track to generate second video media data of the second track, such that the second track is a derived track of the first track.