Description of the issue

usacIndependencyFlag is 1 but MP4 stts or (container format) (container element for independent frame (IF)) does not indicate this frame is independent


ISO IEC 14496-12 (MPEG-4 ISO base media file format):
sample_number: "marking of the sync samples within the stream [...] If the sync sample box is not present, every sample is a sync sample"
group_description_index: "gives the index of the sample group entry which describes the samples in this group"

ISO IEC 23003-3 (USAC):
usacIndependencyFlag: "Meaning of usacIndependencyFlag"