[M4IF Technotes] GMC

[Rob Koenen]

Suzuki-san,
> ISMA is just example, not generic.
> My suggestion is not to add its own levels, that is to define 
> the limitation for the current levels.

A limitation on the current Level definitions is axactly the same
as defining new Levels ...
> I think that 
> 1. the limitation on encoding defined by an assosiation does not 
>    cause the prombles for existing products, and 

I agree in principle.
However, the limitation will then also be exploited in the decoder,
which then does go on to cause problems, because, as you rightly say below,
such a decoder will then not be able to decode all permitted bitstreams
anymore ...
If it is just a limitation on the encoder without consequences for the
decoder then there is no problem at all. There are people today that
claim they support Advanced Simple Profile, while they do not implement
e.g. B frames or 1/4 pel motion compensation. As long as this is only
the encoder, there is no problem with interoperability. The only problem
is with the quality of the encoded video, which is not nearly as good
as it could have been. If these tools, however, are not implemented in 
the DEcoder, then a claim to support Advanced Simple is simply a false
statement (also called "lie").
> 2. the limitation on decoder in the specific association does not
>    cause the prombles, though such decoder could not decode all 
>    standard bitstreams.

Best,
Rob