Description of the issue

(container format) (container element for immediate play-out frame (IPF)) does not indicate this frame is an immediate play-out frame (IPF) but USAC AudioPreRoll is present


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"

ISO IEC 23003-3 (USAC):
AudioPreRoll: "Frames that use AudioPreRoll() [...] are considered to be immediate play-out frames (IPF) and shall be signalled as sync samples"

Possible solution/action

ISO IEC 14496-12:
Fix the muxer in order to correctly fill stss (if non fragmented MP4 file) or trun (if fragmented MP4 file) with this frame number, then remux the content.