[FFmpeg-soc] [soc]: r532 - matroska/matroskaenc.c

[Michael Niedermayer]

On Sat, Jul 28, 2007 at 09:03:42PM +0300, Kostya wrote:
> On Sat, Jul 28, 2007 at 07:09:44PM +0200, Michael Niedermayer wrote:
> > Hi
> > 
> > On Sat, Jul 28, 2007 at 05:43:03PM +0300, Kostya wrote:
> > > On Sat, Jul 28, 2007 at 02:16:23PM +0200, Michael Niedermayer wrote:
> > > > Hi
> > > [...]
> > > > 
> > > > ... as i said getting a good and secure random number is not easy, you 
> > > > cannot use anything that could be usefull for an expoit or anything that
> > > > could by used to identify time or place where encoding happened,
> > > > not the current time, no pointers, ...
> > > > you are left with the video/audio you are going to encode, and some stuff
> > > > we cant easily use like the least significant bits of the time of some
> > > > interrupts
> > > 
> > > What about this?
> > > http://en.wikipedia.org/wiki/UUID
> > 
> > which version of UUIDs?
> > you have 3 choices
> > 1/2 contains the MAC address (this is the most stupid idea so far not to
> >     mention the issue of how to find the MAC address in a portable way)
> 
> That depends on what UUID is used - IIRC this one can be decoded.

?


> 
> > 3/5 are just a md5/sha1 of a string AFAIK which was already suggested
> > 4   is just a random number (with which we are back to square 1 just that we
> >     now can call it UUID)
> > 
> > 
> > what about this?
> > /dev/zero
> 
> The best seed is lower bits of timestamp, especially in nanoseconds - it's
> very random and you can't restore anything useful from it.

we need a _PORTABLE_ solution! me have no millisec precission timer let alone
micro or nano
if portability wasnt an issue we could just use /dev/random

simply using a constant seed is the obvious solution

why would a file need a random/unique id anyway?, especially if all? muxers
create these "random" ids with a 32bit seed from the current time
a 32bit seed means 1 collission in ~64000 files (assuming the 32bit seeds
are really random)
using srand(time(0)) you get 1 second precission, and this will likely
cause additional colissions ...

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I have often repented speaking, but never of holding my tongue.
-- Xenocrates
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