[FFmpeg-devel] CNG (consistent noise generation) patch for AC-3 decoder

Michael Niedermayer michael at niedermayer.cc
Fri Sep 2 23:56:23 EEST 2016

On Fri, Sep 02, 2016 at 01:13:33PM -0700, Jonathan Campbell wrote:
> On 09/02/2016 01:01 PM, Michael Niedermayer wrote:
> >On Fri, Sep 02, 2016 at 10:19:23AM -0700, Jonathan Campbell wrote:
> >[...]
> >>CRC computation isn't fast enough? What should I use then? A sum of
> >>byte values?
> >av_lfg_init() calls av_md5_sum()
> >av_md5_sum() is too slow to be called per ac3 frame
> >
> >[...]
> >
> >
> >_______________________________________________
> >ffmpeg-devel mailing list
> >ffmpeg-devel at ffmpeg.org
> >http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> Then for this to work at better performance, I'm going to have to
> either directly modify the AVLFG struct state (probably not a good
> idea), or add a function to libavutil/lfg.c that allows "fast
> seeding" without the use of MD5 which could probably be something as
> simple as copy the 32-bit seed 16 times through c->state[] with or
> without modification during the loop. Sound good?

yes, something like this
probably spliting the input into 16 parts get 16 CRCs and use them
instead of replication is probably better

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

You can kill me, but you cannot change the truth.
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