[M4IF Technotes] some queries on creation of fragmented movies

[Chandra Sekhar Reddy]

Hi,
Requesting answers for some queries
regarding creation of fragmented movies explained in:
the document "WG 11/N4854 or WG 1/N2538"
titled "Proposed Revised Common Text Multimedia File Format
Specification"
dated "21 March 2002"
and
Section:3.8 - Construction of fragmented movies
in the document "MPEG2003/N5651"
titled "Amendment 1 to the ISO Base Media File Format"
dated "March2003, Pataya, Thailand"
1.  The document states Zero or more 'traf' boxes per 'moof' box.
    What is the possibility of zero number of 'traf' boxes in a 'moof'
box?
    Moreover, while constructing a movie, the duration of tracks can be
different.
    Old tracks may expire and new tracks may start, in which case the
number of 'traf' in different 'moof' can be different.
    The answer for this may be connected to the query-2 below!
2. Is there a possibility to create movies in which some tracks are
non-fragmented and some are fragmented?
    If yes, the requirement of number of 'trex' boxes being equal to
"Exactly one per track in the movie box" is invalid!
3. What is the structure format (member parameters) for the atom/box
'mfra'?
    Is it similar to 'stss' (sync-sample-box) in 'stbl', replicated for
all traks?
4. Consider a video-encoder generates a stream with less number of
intra-frames (time/buffer-distance between intra-frames is large),
    or a video-encoder is using "Advanced Intra Refreshing" of MBs,
where intra-frames are still more distant apart,
    then,
    The requirement (or is it only recommendation only?) that
    the first sample in each 'traf' box to be a randon-access-point
(intra-frame for video!),
    may increase the size of data (both meta-data and media-data) per
fragment ('moof'),
    and this fragment's meta-data to be analyzed and written into the
'moof' box.
    Should a DEVICE WITH LESS MEMORY, that can not buffer data for a
long-time,
    go for compromise between the intra-period (in effect, compression!)
and fragment size?
Regards,
Chandra
DSP/MultiMedia Group,
TATA ELXSI Ltd,
BANGALORE, INDIA.