why I can't find video-objetc-layer of mpeg4-2 video stream after qtdemux?

[Zhao, Halley]

I connects a mpeg4-2 video parser/codec after qtdemux, the first start_code I could find is gop (0xb3) or vop (0xb6).
Why isn't there video-object-layer header (0x20)?

How could I parse vop with the necessary data in vol?
Does it mean something wrong in the stream? Or I should construct a vol with default value? (what are the default value?)
However, totem can playback the stream.

I don't think it is a h263 stream with short header since it doesn't start with 16 bits '0', but 23 bits'0'
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