[M4IF Technotes] Sub-part of a presentation

[Richard Shields]

Hi Chris, all,
> 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.

So, the OD stream in the main file creates a video object and an audio
object that both have url references to the same file that contain a video
stream and an audio stream.  But how would that file that contains the audio
and video be constructed?  Would it contain just the elementary streams for
audio and video?  It would have to contain an iods according to 13.2.3.4.
And, according to 8.6.4.1 the IOD contained in the iods must refer to at
least one stream but it cannot refer to both the audio and the video stream
according to 8.7.1.2.  So, how is it accomplished?
> >
> > 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.
> 

13.2.3.4 states that an iods contains *an* Object Descriptor or *an* Initial
Object Descriptor.  So, from that, I understand that the iods contains only
one IOD or OD.  You cannot string together a series of OD's in the iods like
you can in an ObjectDescriptorUpdate command.  Would anyone disagree with
that statement?  It would have been nice if you could string together all of
your objects in the iods that would be in existance at time 0 so you would
not have to have an OD stream.
I don't agree with your statement that IOD's and OD's are composed of OD
commands.  Rather, IOD's and OD's are composed of component descriptors.  OD
commands refer to those elements in listed in Table 2 in 14496-1.
-Richard