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

Jonathan Campbell jonathan at impactstudiopro.com
Fri Sep 2 23:13:33 EEST 2016

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?

Jonathan Campbell

More information about the ffmpeg-devel mailing list