[M4IF Technotes] Sub-part of a presentation

[Christopher Wendt]

(I forgot to forward this to the rest of the list, sorry)
Hi Richard, all,
> Section 13.2.3.4 of 14496-1 mentions that a file that contains an IOD in
the
> esds atom but no BIFS track is a sub-part of a presentation.  Given that,
is
> it possible to create a file that is a sub-part of a presentation where
the
> file contains both video and audio streams?
Yes.
> Since the IOD cannot include a
> video stream and an audio stream because of section 8.7.1.2 one would need
> to create an OD stream to create objects for each media type.  But,
8.7.1.4
> indicates that an OD cannot contain an OD stream without a BIFS stream.
So,
> if you include an BIFS stream in the IOD to comply with 8.7.1.4 then it is
> no longer a sub-part of a presentation.  Am I misinterpreting the
> specifications?
You can have, for example, two (or more) mp4 files, one with an IOD
containing the BIFS scene and the OD which references by URL the second
(third, fourth,...) file (the "sub-part") containing the Video/Audio.
>
> Other related questions:
>
> Can an iods atom contain multiple OD's?  13.2.3.4 seems to indicate that
it
> can only contain one.
In general, for a self contained presentation, an IOD should reference 1
BIFS and 1 OD stream.  If you want to reference multiple OD streams (which
would usually mean you are inlining multiple scenes) you would use a URL
references.  Look at 8.7.3 in 14496-1.
>
> Can an iods atom contain OD commands?
Both IOD's and OD's are composed of OD commands, so yes of course. But for
IOD you are only going to have 2 ODUpdates for the BIFS and OD.
>
> Is it valid to have an IOD that doesn't refer to any elementary streams? I
> have seen this in some .mp4 files but it does not seem to follow 8.6.4.
No, if the IOD doesn't refer to any ES's then there is nothing.
-Chris
-------------------------------------------------------------
Christopher Wendt,  avipix, llc
chris   avipix.com
(732) 682-5549
http://www.avipix.com