[FFmpeg-soc] [soc]: r532 - matroska/matroskaenc.c
michaelni at gmx.at
Sat Jul 28 23:56:54 CEST 2007
On Sat, Jul 28, 2007 at 04:23:45PM -0400, David Conrad wrote:
> On Jul 28, 2007, at 3:10 PM, Michael Niedermayer wrote:
> > 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:
> >>> 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 ...
> mkvmerge uses UuidCreate() on Windows and reads from /dev/urandom on
> *nix, with a fallback to rand() if either fails (seeded by
> GetTickCount() on Windows or gettimeofday() on *nix.)
> The unique ID can be used by a couple of elements (PrevUID, NextUID,
> and ChapterSegmentUID) to refer to a segment in a different file (or
> the same file, there can be more than one segment per file) to create
> a playlist of segments.
> I don't think it's necessary to try for a completely unique ID, the
> SHA-1 hash of a couple of frames would be enough imo, given how
> infrequently these options are used (I'll implement this shortly if
> there are no objections.) I just didn't want every segment UID to be
> identical unless the user requests it via bitexact.
no objections ...
though maybe a crc or adler32 checksum would be a better option
as they are faster
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Dictatorship naturally arises out of democracy, and the most aggravated
form of tyranny and slavery out of the most extreme liberty. -- Plato
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