[FFmpeg-devel] AMR-NB decoder

[Michael Niedermayer]

On Wed, Aug 12, 2009 at 09:54:14PM +0100, Colin McQuillan wrote:
> 2009/8/12 Robert Swain <robert.swain at gmail.com>:
> > Hey,
> >
> > 2009/8/10 Colin McQuillan <m.niloc at googlemail.com>:
> >
> > [...]
> >
> >> I have tried to address every other comment made in the thread. The
> >> main changes are cosmetics, using fixed point tables to save space,
> >> and keeping the algebraic codebook vector sparse until
> >> anti_sparseness.
> >>
> >> amrnb-decoder-r2.patch uses high-pass-filterf.patch, agc-3.patch, and
> >> circ-addf.patch.
> >
> > circ-addf committed after editing the comments a little and discussing
> > them with Colin on IRC. I think maybe the high-pass filter should be
> > made at least somewhat generic as the missing QCELP postfilter uses a
> > filter that is the same order but with different coefficients. I think
> > using the stuff from iirfilter.{c,h} would be overkill for this
> > purpose. I'm discussing this with Colin too.
> >
> > Regards,
> > Rob
> 
> Here's a more general ff_acelp_high_pass_filterf.

>  acelp_filters.c |   18 ++++++++++++++++++
>  acelp_filters.h |   16 ++++++++++++++++
>  2 files changed, 34 insertions(+)
> f3c59c35439591944d3e0db69adc7158ecfd1abf  high-pass-filterf-2.patch
> Index: libavcodec/acelp_filters.c
> ===================================================================
> --- libavcodec/acelp_filters.c	(revision 19634)
> +++ libavcodec/acelp_filters.c	(working copy)
> @@ -93,3 +93,21 @@
>          hpf_f[0] = tmp;
>      }
>  }
> +
> +void ff_acelp_high_pass_filterf(float *buf,
> +                                const float zero_coeffs[2],
> +                                const float pole_coeffs[2],
> +                                float gain, float mem[2], int n)
> +{
> +    int i;
> +    float tmp;
> +
> +    for (i = 0; i < n; i++) {

> +         tmp = buf[i] - pole_coeffs[0] * mem[0] - pole_coeffs[1] * mem[1];
> +         buf[i] = tmp + zero_coeffs[0] * mem[0] + zero_coeffs[1] * mem[1];
> +         buf[i] *= gain;

float tmp= gain*buf[i] - pole_coeffs[0] * mem[0] - pole_coeffs[1] * mem[1];
buf[i]   =         tmp + zero_coeffs[0] * mem[0] + zero_coeffs[1] * mem[1];

and yes iam in favor of such a generic function

[...]

> Index: libavcodec/acelp_filters.h
> ===================================================================
> --- libavcodec/acelp_filters.h	(revision 19634)
> +++ libavcodec/acelp_filters.h	(working copy)
> @@ -81,4 +81,20 @@
>  void ff_acelp_high_pass_filter(int16_t* out, int hpf_f[2],
>                                 const int16_t* in, int length);
>  
> +/**
> + * Apply an order 2 rational transfer function in-place.
> + *
> + * @param samples [in/out]
> + * @param zero_coeffs z^-1 and z^-2 coefficients of the numerator
> + * @param pole_coeffs z^-1 and z^-2 coefficients of the denominator
> + * @param gain scale factor for final output
> + * @param mem intermediate values used by filter (should be 0 initially)
> + * @param n number of samples
> + */
> +void ff_acelp_high_pass_filterf(float *samples,

i think the name is very poor because it describes the current use of
the function and not what the function does
(i mean its like find_length_of_square_from_area() vs. sqrt())

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When the tyrant has disposed of foreign enemies by conquest or treaty, and
there is nothing more to fear from them, then he is always stirring up
some war or other, in order that the people may require a leader. -- Plato
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