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

[Michael Niedermayer]

On Fri, Sep 02, 2016 at 04:49:54PM -0700, Jonathan Campbell wrote:
> 
> On 09/02/2016 04:37 PM, Michael Niedermayer wrote:
> >On Fri, Sep 02, 2016 at 04:05:44PM -0700, Jonathan Campbell wrote:
> >>On 09/02/2016 01:56 PM, Michael Niedermayer wrote:
> >>>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
> >>>
> >>>
> >>>[...]
> >>>
> >>>
> >>>_______________________________________________
> >>>ffmpeg-devel mailing list
> >>>ffmpeg-devel at ffmpeg.org
> >>>http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> >>How's this:
> >>
> >>void av_lfg_init_from_data(AVLFG *c, const unsigned char *data,
> >>unsigned int length) {
> >>     unsigned int beg, end, segm;
> >>     const AVCRC *avcrc;
> >>     uint32_t crc = 0;
> >1 might be better
> >
> >should be ok otherwise didnt review it deeply though
> >
> >[...]
> >
> >
> >_______________________________________________
> >ffmpeg-devel mailing list
> >ffmpeg-devel at ffmpeg.org
> >http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> Finished patch. Hopefully it won't get garbled as an attachment.
> 
> Jonathan Campbell
> 

>  libavcodec/ac3dec.c       |    7 +++++++
>  libavcodec/ac3dec.h       |    4 ++++
>  libavcodec/ac3dec_fixed.c |    1 +
>  libavcodec/ac3dec_float.c |    1 +

>  libavutil/lfg.c           |   27 +++++++++++++++++++++++++++
>  libavutil/lfg.h           |    5 +++++

should be in a different patch
also needs minor version bump and APIChanges update

also please generate patches with git format-patch or git send-email
see the respective man pages
(otherwise they woul be lacking commit messages)

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Why not whip the teacher when the pupil misbehaves? -- Diogenes of Sinope
-------------- 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/20160903/3921194f/attachment.sig>