group_description_index
gives the index of the sample group entry which describes the samples in this group
ISO IEC 14496-12 (MPEG-4 ISO base media file format):moof/traf/sbgp
(container format) (container element for independent frame (IF)) indicates this frame is an independent frame (IF) but (content format) (content element) (content field) (value ) indicates this frame is not an independent frame (IF)
(container format)
(container element for independent frame (IF))
(content format)
(content element)
(content field)
(value )