[FFmpeg-devel] [PATCHv3 1/3] lavu/rand: add 64 bit random number generator

[Michael Niedermayer]

On Tue, Mar 15, 2016 at 11:37:30PM +0000, Derek Buitenhuis wrote:
> On 3/15/2016 10:26 PM, Ganesh Ajjanagadde wrote:
> > If one wants good Gaussian samples, then yes, I need a 64 bit rng.
> > Please also note that I can use av_lfg_get, it does not result in
> > slowdown, since speed benefits here come from the ziggurat algo.
> > Concretely, it is 82 cycles vs 81 cycles; too little to clearly
> > distinguish. I was just not too happy with av_lfg_get << 32 |
> > av_lfg_get as it resulted in some bad values in the Anderson Darling
> > tests.
> 
> "If one wants good Gaussian samples" doesn't explain at all how it is
> relevant to a set of multimedia libraries like FFmpeg. Why do we want
> those? That is the relevant information which should be mentioned
> in the commit message.

i cant speak for AACs need for gaussian RNG but for example
libavfilter/vf_noise.c supports gaussian noise and as i realize now
does so by duplicating a BMG
audio noise generation similarly would need some gausian RNG to
generate gaussian noise.
The random samples should be good enough to appear random to humans or
any subsequent filters (it would be bad if artifacts appear after
subsequent filters due to defects in the priorly added noise)

so i think there are cases in multimedia where gausian noise is needed,
"good Gaussian samples" is too vague but as a user i would want a
noise filter to produce good noise

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The real ebay dictionary, page 1
"Used only once"    - "Some unspecified defect prevented a second use"
"In good condition" - "Can be repaird by experienced expert"
"As is" - "You wouldnt want it even if you were payed for it, if you knew ..."
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 181 bytes
Desc: Digital signature
URL: <http://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20160316/3eba2bbf/attachment.sig>