Re: [Cellar] VINT_DATA of all ontes

Dave Rice <dave@dericed.com> Thu, 07 June 2018 14:50 UTC

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From: Dave Rice <dave@dericed.com>
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Subject: Re: [Cellar] VINT_DATA of all ontes
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> On Jun 6, 2018, at 9:49 PM, Michael Richardson <mcr+ietf@sandelman.ca> wrote:
> 
> 
> ebml says in section 7:
> 
>     Additionally,
>     an "Element ID" with binary encoding of "1111 1111" is invalid since
>     the "VINT_DATA" section is set to all one values, whereas an "Element
>     ID" with binary encoding of "0100 0000 0111 1111" stores a
>     semantically equal "VINT_DATA" and is the shortest possible
>     "VINT" encoding.
> 
> It seems that there is a prohibition on VINT_DATA that is all ones.
> I can't find a place in section 6 that says this.

Just before your quote, I see:

"The VINT_DATA component of the Element ID MUST NOT be either defined or written as either all zero values or all one values.”


> Is this a restriction on
> all VINT_DATA, or just ones used for Element ID?

This is specific to the Element ID. An all-one VINT_DATA in Element Data Size (also a VINT) means that the size is unknown. See:

   An "Element Data Size" with all "VINT_DATA" bits set to one is
   reserved as an indicator that the size of the "EBML Element" is
   unknown.  The only reserved value for the "VINT_DATA" of "Element
   Data Size" is all bits set to one.

Dave