[FFmpeg-devel] [PATCH] Common ACELP code & G.729 [1/7] - filters

[Michael Niedermayer]

On Fri, May 09, 2008 at 01:35:31PM +0700, Vladimir Voroshilov wrote:
> Michael Niedermayer wrote: 
> > On Wed, May 07, 2008 at 10:23:50AM +0700, Vladimir Voroshilov wrote:
> > [...]
> 
> [...]
> 
> > > >  > >    + MULL(hpf_f[1], -7667);                     /* (13.13) = (13.13) * (0.13) */
> > > >  > >    + 7699 * (in[i] - 2*in[i-1] + in[i-2]);      /* (14.13) =  (0.13) * (14.0) */
> > > >  > >
> > > >  > >  out[i] = av_clip_int16((t + 0x800) >> 12);      /* (15.0) = 2 * (13.13) = (14.13) */
> > > >  > >
> > > >  > >  hpf_f[1]= hpf_f[0];
> > > >  > >  hpf_f[0]= t;
> > > >  >
> > > >  > This will require either two samples before start in "in" buffer, copied from
> > > >  > the previous subframe or
> > > >  
> > > >  yes, i thought that would be just something like
> > > >  memcpy(in-2, in+len-2, 2*sizeof(*in))
> > > >  
> > > >  ?
> > > >  
> > > >  If so that should be simpler than it is currently
> > > >  
> > > Current code work as following:
> > > 
> > > context
> > > {
> > >   syn_filter_data
> > >   post_filter_data
> > >   hpf_z
> > >   hpf_z
> > > }
> > > 
> > > mainloop
> > >   {
> > >    ...
> > > 1  syn_filter(syn_filter_data+10)
> > > 2  memcpy(syn_filter_dta+10, syn_filter_data+subframe_size,10)
> > > 3  postfilter(syn_filter_data+10, postfilter_data) 
> > > 6  high_pass_filter(out_data,syn_filter_data+10,hpf_z,hpf_f)
> > > 7 }
> > > 
> > > syn_filter requires first 10 items of previous data saved just after call to it.
> > > 
> > > postfilter does not requires previous data (it uses post_filter_data as such),
> > > but it changes contents of syn_filter data (from 10 to the end of buffer).
> > > 
> > > high_pass_filter (in your suggestion) requires previous data in buffer,
> > > but buffer does not contains it already (were overwritten in line 2)
> > > 
> > > The problem is in fact that syn_filter requires unfiltered past data, while
> > > high_pass_filter requires them filtered with postfilter.
> > > 
> > > Moreover, since top of buffer already contains data saved for future
> > > syn_filter call, i cant save there
> > > copy of hpf_z (can't do memcpy(in,hpf_z) inside filter).
> > 
> > If postfilter would be writing in a "new" buffer that problem should disapear.
> > 
> > also one can easily chain filters so each has previous samples with few
> > memcpy() and little buffer space:
> > 
> > caAAAA
> > db....
> > 
> > c....A
> > dbBBBB
> > 
> > cCCCCA
> > d....B
> > 
> > ....CA
> > dDDDDB
> > 
> > ....CA
> > ....DB
> > 
> > CA....
> > DB....
> > 
> > 
> > [...]
> > 
> 
> Done. One temp buffer in main loop and two small buffers for
> keeping data between subframes are added.
> Postfilter is not yet touched.
[...]
> +    /* Since there are few pulses over all subframe (i.e. almost all
> +       fc_in[i] are zero, in case of G.729D it is only two non-zero
> +       samples of total 40), it is faster to swap two loops and process
> +       non-zero samples only. This will reduce number of multiplications
> +       from 40*40 to 2*40 for G.729D */

didnt you want to change this?



[...]
> +void ff_acelp_high_pass_filter(
> +        int16_t* out,

> +        int* hpf_f,

int hpf_f[2],

is clearer

patch looks ok except the 2 things above

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

No great genius has ever existed without some touch of madness. -- Aristotle
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