Re: [Schrodinger-devel] Re: Fix up tables and escape codes in Dirac

[Ralph G. <gi...@xi...>]

On Fri, Feb 03, 2006 at 05:09:25PM +0000, Tim Borer wrote:

> The idea is that the sequence parameters will remain constant during 
> a sequence. This allows a decoder to build up confidence over a 
> channel with errors and reject erroneous sequence parameters. This 
> doesn't mean that all the frames could be replayed but it should stop 
> gross errors in decoding and help prevent decoder crashes.

My point was that, after a seek in an native bitstream, there's no way 
to distinguish corrupt parameters in an AU header from having crossed
a sequence boundary. In a linear scan it's different, since you'll see
the stop sequence or, if it's corrupt, likely notice the hole from
the loss of reading frame. That, detecting truncation, and discouraging
people from changing parameters all the time seem reasons enough to keep 
the stop sequence parse unit.

I agree that using a 'repeat' flag in the Access Unit Header instead 
offers no advantages.

> Escape sequence are rare. I would expect most fixup table to include 
> no more than a single entry. (There may be exception of untypical, 
> pathological sequences). So I guess, maybe, it is worth keeping two 
> different parse codes (for with and without fixup tables) to save 
> bitrate for low resolutions. But I'm still undecided (I like the 
> simplicity of always having a fixup table) and have had no other 
> feedback on this.

Well, no help there. I like the simplicity too, but it would be nice to
have another opinion.

Cheers, 
 -r

> P.S. Sorry for slow reply 

No problem. There's been lots of that on both sides...