[FFmpeg-devel] [PATCH] AAC decoder

[Michael Niedermayer]

On Fri, May 23, 2008 at 04:06:10PM +0100, Robert Swain wrote:
> 2008/5/21 Robert Swain <robert.swain at gmail.com>:
> > 2008/4/2 Michael Niedermayer <michaelni at gmx.at>:
> >> On Tue, Apr 01, 2008 at 04:56:48PM +0200, Andreas ?man wrote:
> >>> Andreas ?man wrote:
> >
> > [...]
> >
> >>> +/**
> >>> + * Decode scale_factor_data
> >>> + * reference: Table 4.47
> >>> + */
> >>> +static int scale_factor_data(AACContext * ac, GetBitContext * gb, float mix_gain, unsigned int global_gain, ics_struct * ics, const int cb[][64], float sf[][64]) {
> >>
> >> Maybe rename the function to what the comment says
> >>
> >>
> >>> +    int g, i;
> >>> +    unsigned int intensity = 100; // normalization for intensity_tab lookup table
> >>> +    int noise = global_gain - 90;
> >>> +    int noise_flag = 1;
> >>> +    ics->intensity_present = 0;
> >>> +    for (g = 0; g < ics->num_window_groups; g++) {
> >>> +        for (i = 0; i < ics->max_sfb; i++) {
> >>> +            if (cb[g][i] == ZERO_HCB) {
> >>> +                sf[g][i] = 0.;
> >>
> >>> +            } else if (cb[g][i] == INTENSITY_HCB || cb[g][i] == INTENSITY_HCB2) {
> >>> +                ics->intensity_present = 1;
> >>> +                intensity += get_vlc2(gb, ac->mainvlc.table, 7, 3) - 60;
> >>> +                if(intensity > 255) {
> >>> +                    av_log(ac->avccontext, AV_LOG_ERROR,
> >>> +                           "Intensity (%d) out of range", intensity);
> >>> +                    return -1;
> >>> +                }
> >>> +                sf[g][i] = ac->intensity_tab[intensity];
> >>> +            } else if (cb[g][i] == NOISE_HCB) {
> >>> +                if (noise_flag) {
> >>> +                    noise_flag = 0;
> >>> +                    noise += get_bits(gb, 9) - 256;
> >>> +                } else {
> >>> +                    noise += get_vlc2(gb, ac->mainvlc.table, 7, 3) - 60;
> >>> +                }
> >>> +                sf[g][i] = pow(2.0, 0.25 * noise) * ac->sf_scale;
> >>> +            } else {
> >>> +                global_gain += get_vlc2(gb, ac->mainvlc.table, 7, 3) - 60;
> >>> +                if(global_gain > 255) {
> >>> +                    av_log(ac->avccontext, AV_LOG_ERROR,
> >>> +                           "Global gain (%d) out of range", global_gain);
> >>> +                    return -1;
> >>> +                }
> >>> +                sf[g][i] = ac->pow2sf_tab[global_gain];
> >>> +            }
> >>
> >> The identical code is implemented here 3 times, 2 times with seperate
> >> LUTs and once by directly calling pow()
> >> The differenes look like bugs. like forgetting to check validity or
> >> performing the scaling needed for the float2int16 transform.
> >>
> >> if(cb[g][i] == NOISE_HCB && noise_flag-- > 0)
> >>    gain[index] += get_bits(gb, 9) - 256;
> >> else
> >>    gain[index] += get_vlc2(gb, ac->mainvlc.table, 7, 3) - 60;
> >> if(gain[index] > 255)
> >>    ...
> >> sf[g][i] = ac->pow2sf_tab[gain[index]];
> >
> > I tried this and audibly it sounds fine on a few files I tested. I
> > want to compare the two tables and pow() * ac->sf_scale call before
> > submitting a patch though.
> 
> The intensity case is different to the noise and global cases. See
> attached patch.

It may be different, but it has to be scaled by sf_scale somewhere.
intensity_tab is not and i dont see it anywhere afterwards either.
if intensity_tab would be scaled then the difference would disapear.
all just IMHO and after a quick look ...

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

Freedom in capitalist society always remains about the same as it was in
ancient Greek republics: Freedom for slave owners. -- Vladimir Lenin
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