Written against the glTF 2.0 spec.


In order to support timed data access, the buffer element is extended to provide functionality of a circular buffer. The extension is named “MPEG_buffer_circular” and may be included as part of the “buffers” structures. Buffers that provide access to timed data shall include the “MPEG_buffer_circular” extension.

glTF Schema Updates


The circular buffers are defined by adding the MPEG_buffer_circular extension to any glTF buffer.

The following table lists the semantics of the properties of an MPEG_buffer_circular extension:

Type Description Required
count integer recommended number of frames in buffer. No
media integer reference to the MPEG media that acts as source. Yes
tracks array tracks from the source that should be used. No


The count field provides the recommended number of sequential frames that need to be offered by this circular buffer to the presentation engine. This information may be used by the MAF to setup the circular buffer towards the presentation engine.


Index of the MPEG media entry that will be used as the source for the input data to this buffer.


Index of a track of a MPEG media entry, indicated by source and listed by MPEG_media extension, used as the source for the input data to this buffer. When tacks element is not present, potentially all tracks of the MPEG_media entry listed by source element are needed to generate the input data to this buffer. NOTE: When more than one track is listed by tracks element, the corresponding buffer is in active state and the MAF is informed that the corresponding tracks are needed as source for the input buffer, then the MAF could optimize the delivery of multiple tracks.

Interaction with other extensions

Circular buffers are described by timed accessors.

JSON Schema


Known Implementations