[XviD-devel] Re : Various bugs

[Christoph Lampert]

On Thu, 17 Feb 2005, Fr?d?ric DALLEAU wrote:
> I still have questions.
> What do you consider as being a conformant stream? It has a different 
> meaning in decoding and encoding. In decoding, you can assume no frame 
> is altered, all frames comes from the same stream, no frames are 
> skipped... In encoding, apart from having all images the same size, I 
> don't see other assumption one can make.
> Is there a way to validate a frame and make sure it is legal?

Hi,

I meant a conformant compressed stream, so a sequence of bytes which 
conforms to the specs of MPEG-4, i.e. the compression is done correctly. 
This includes the millions of restrictions that MPEG-4 set, so all 
"runs" of a block cannot add up to more than 64, or the sequence cannot 
start with a B-frame, or this stuff. 
If you have a broken encoder, or a noisy channel which alters bits or 
something, the file might not be compliant anymore. In theory, the decoder 
should never crash, no matter what's the input it, but I'm sure XviD is 
far from that robustness. If a file contains the encoded information of 
"run=32", although there are only fewer possible coeffient positions left, 
it'll write past the out buffer etc. 

gruel