[M4IF Technotes] Sub-part of a presentation

[Christopher Wendt]

Hi Richard, all,
> 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?
>
There is a couple ways you can do this.
Your main file has an IOD and BIFS and OD tracks.
The OD track contains an OD command with the video OD and audio OD.
One way is:
Those OD's contain urls to the remote OD's.
The remote file contains a root OD (not IOD). which has the OD information
for the Audio and Video ES's.
Another way is:
Those OD's contain urls to the remote ES's directly in which case the remote
file doesn't need to contain any OD or IOD.
A third way:
You can also have a remote URL contained in the file format Data Reference
atom.
> > > Can an iods atom contain OD commands?
Sorry, let me correct myself,  an IOD is an OD with the P&L info in front,
so no it cannot contain OD commands.  (But the other way around is true, an
OD command can contain an IOD)
The OD stream itself is composed of OD commands which contain OD's.
>
> 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.

Right, the purpose of the IOD is to initialize the presentation, and most
likely the IOD will be transmitted out of band, which is why it exists and
does not contain all of the presentation information.
-Chris
-------------------------------------------------------------
Christopher Wendt,  avipix, llc
chris   avipix.com
(732) 682-5549
http://www.avipix.com