[M4IF Technotes] Descriptor Length Field

[Chandra Sekhar Reddy]

Hi Trevor,
The Descriptors are derived from *BaseDescriptor*
These Descriptors
--start with their identifier (the descriptor-tag 1-byte field)
--followed by *sizeOfInstance* (the length-field in question!)
This sizeOfInstance gives the total-number of bytes occupied by the
descriptor,
*excluding* the tag-field and sizeOfInstance-field.
Refer to "14.3.3 Expandable classes" -- read the meaning of sizeOfInstance.
******************************
int sizeOfInstance = 0;
bit(1) nextByte;
bit(7) sizeOfInstance;
while(nextByte) {
    bit(1) nextByte;
    bit(7) sizeByte;
    sizeOfInstance = sizeOfInstance<<7 | sizeByte;
}
******************************
Regards,
Chandra
Trevor wrote:
> Dear Experts,
>
> According to "ISO/IEC 14496-1:2001", the syntax of any descriptor does
> NOT contain a length field. But in the annex J (Graphical representation
> of osbject descriptor and sync layer syntax), there is a length field
> right after TAG field. Could anyone here tell me what this length field
> represents and how it is encoded?
>
> Thanks in advance,
> Trevor
>
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