[x264-devel] Re: [patch] VUI extended corrected

[Mike Matsnev]

Christian Heine wrote:
> Before we going on, lets recap, and find a common ground again. Here are 
> my three statements.
> 
> - SAR never changes since the time the image is digitised, unless the it 
> is resized.
> - The cropping rectange feature can be seen a superset of the overscan 
> feature. Overscan effectively results in an additional cropping rect.
> - DAR always refers to the image contained in the cropping rectangle, 
> that results from both the original cropping rectangle and the overscan 
> cropping.
> 
> I admit that the phrase "use a different SAR" is not clear, it should 
> read "specify a different SAR". But what we were really arguing about 
> are statements 2 and 3. But the spec is clear about this.
> 
> My point boils down to this: _If_ the DAR refers to the image contained 
> in the cropping rectangle, and the cropping rectangle changes (because 
> of the overscan) but DAR should stay the same, then SAR must have been 
> different in the first place.
I think you misunderstand overscan. All the flag does it tell the decoder/display
that it's ok to hide some part of the picture, nothing is said about changing SAR,
etc. The typical use for this feature would be an STB connected to the TV set. It
could have two modes of operation. By default it outputs a normal
signal to TV, so it overscans. In the other mode it scales down the picture and adds
black borders, so even with TV overscan the entire image is visible. But this
scaling does not change SAR and DAR in any way.

/Mike

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