[M4IF Technotes] Very basic question about video bitstream syntax and ES definitio ns

[Larry Pearlstein]

Dear M4IF community members,
I'm wondering about the syntax that I've found in MPEG-4 video bitstreams.
I see the following:
0000 0101   video_object_start_code
0000 0120   video_object_layer_start_code
00c8        = "0000 0000 1100 1000"     >   random_acc = 0
                                            video_object_type_indication =
0x01, simple object type
                                            is_object_layer_id = 1
                                            verid = 0010,
                                            priority = 001
                                            etc.
My confusion comes from the fact that it seems that the syntax of the file
begins in the middle of the VisualObject syntax.  Perhaps I've missed some
text that suggests that this is allowed, suggested, etc?
In the conformance spec it says:
	"A bitstream is the coded representation of one layer of a single
visual object."
Based on this definition, I'd expect to find a visual_object_start_code at
the beginning of the file.
Also, I'm confused about the definition about an MPEG-4 "Elementary Stream".
Figure 6-12 suggests that a Visual Object Layer is an elementary stream.  I
would imagine that a VideoObjectLayer is a type of Visual Object Layer,
right?
But the text suggests that a VideoObjectLayer contains configuration
information that is not part of an elementary stream.  Also,
VideoObjectLayer is hierarchically above the 5 functions that are enumerated
as "entry points" for elementary streams.
So - is a VideoObjectLayer an Elementary Stream?  Is an MPEG-4 video
bitstream file an elementary stream?  Is an MPEG-4 video bitstream file a
VideoObjectLayer, etc?
Thanks for any help.  Also, please forgive me if this isn't the appropriate
forum for this question, it's the first time I've posted.
				Thanks,
				Larry Pearlstein
				ATI
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