The MfhdBox field and related fields specify the fragment's position in the sequence for the track. The syntax of the MfhdBox field is a strict subset of the syntax of the Movie Fragment Header Box that is defined in [ISO/IEC-14496-12].
MfhdBox (variable): The metadata container for the sequence information for the track.
MfhdBoxLength (4 bytes): The length of the MfhdBox field, in bytes, including the MfhdBoxLength field. If the value of the MfhdBoxLength field is %00.00.00.01, the MfhdBoxLongLength field MUST be present.
MfhdBoxLongLength (8 bytes): The length of the MfhdBox field, in bytes, including the MfhdBoxLongLength field.
SequenceNumber (4 bytes): An ordinal for the fragment in the track timeline. The SequenceNumber value for a fragment that appears later in the timeline MUST be greater than the value for a fragment that appears earlier in the timeline, but SequenceNumber values for consecutive fragments are not required to be consecutive.
The syntax of the fields that are defined in this section, specified in ABNF [RFC5234], is as follows.
MfhdBox = MfhdBoxLength MfhdBoxType [MfhdBoxLongLength] MfhdBoxFields MfhdBoxChildren MfhdBoxType = %d109 %d102 %d104 %d100 MfhdBoxLength = BoxLength MfhdBoxLongLength = LongBoxLength MfhdBoxFields = SequenceNumber SequenceNumber = UNSIGNED_INT32 MfhdBoxChildren = *( VendorExtensionUUIDBox )