[FFmpeg-devel] [PATCH] AAC decoder round 8

Michael Niedermayer michaelni
Fri Aug 15 13:09:11 CEST 2008


On Fri, Aug 15, 2008 at 09:04:24AM +0100, Robert Swain wrote:
> 2008/8/15 Michael Niedermayer <michaelni at gmx.at>:
> > On Fri, Aug 15, 2008 at 01:32:08AM +0100, Robert Swain wrote:
> >> $subj
> >>
> >> There's not much left to commit now! :D
> >
> > ok
> 
> All committed. Just to make it easier for me and/or you to keep track
> of, here's another patch attached with the remaining hunks.
> 
> Regards,
> Rob

> Index: libavcodec/aac.c
> ===================================================================
> --- libavcodec/aac.c	(revision 14774)
> +++ libavcodec/aac.c	(working copy)
[...]
> @@ -605,6 +616,44 @@
>  }
>  
>  /**
> + * Decode Temporal Noise Shaping data; reference: table 4.48.
> + *
> + * @return  Returns error status. 0 - OK, !0 - error
> + */
> +static int decode_tns(AACContext * ac, TemporalNoiseShaping * tns,
> +        GetBitContext * gb, const IndividualChannelStream * ics) {

> +    int w, filt, i, coef_len, coef_res = 0, coef_compress;

useless init ?


> +    const int is8 = ics->window_sequence[0] == EIGHT_SHORT_SEQUENCE;
> +    const int tns_max_order = is8 ? 7 : ac->m4ac.object_type == AOT_AAC_MAIN ? 20 : 12;
> +    for (w = 0; w < ics->num_windows; w++) {
> +        tns->n_filt[w] = get_bits(gb, 2 - is8);
> +
> +        if (tns->n_filt[w])
> +            coef_res = get_bits1(gb) + 3;
> +
> +        for (filt = 0; filt < tns->n_filt[w]; filt++) {
> +            tns->length[w][filt] = get_bits(gb, 6 - 2*is8);
> +

> +            if ((tns->order[w][filt] = get_bits(gb, 5 - 2*is8)) <= tns_max_order) {
> +                tns->direction[w][filt] = get_bits1(gb);
> +                coef_compress = get_bits1(gb);
> +                coef_len = coef_res - coef_compress;
> +                tns->tmp2_map[w][filt] = tns_tmp2_map[2*coef_compress + coef_res - 3];

the 3 can be moved to "coef_len = coef_res - coef_compress + 3"


> +
> +                for (i = 0; i < tns->order[w][filt]; i++)
> +                    tns->coef[w][filt][i] = get_bits(gb, coef_len);

tns->coef is only used to index into tmp2_map thus
tns->coef could already contain the values from tmp2_map
this also would make the tmp2_map field unneeded in the struct


> +            } else {
> +                av_log(ac->avccontext, AV_LOG_ERROR, "TNS filter order %d is greater than maximum %d.",
> +                       tns->order[w][filt], tns_max_order);
> +                tns->order[w][filt] = 0;
> +                return -1;
> +            }

if(... > tns_max_order){
    ...
    return -1
}
...

seems cleaner to me


> +        }
> +    }
> +    return 0;
> +}
> +
> +/**
>   * Decode Mid/Side data; reference: table 4.54.
>   *
>   * @param   ms_present  Indicates mid/side stereo presence. [0] mask is all 0s;

> @@ -1067,6 +1116,71 @@
>  }
>  
>  /**
> + * Decode Temporal Noise Shaping filter coefficients and apply all-pole filters; reference: 4.6.9.3.
> + *
> + * @param   decode  1 if tool is used normally, 0 if tool is used in LTP.
> + * @param   coef    spectral coefficients
> + */
> +static void apply_tns(float coef[1024], TemporalNoiseShaping * tns, IndividualChannelStream * ics, int decode) {
> +    const int mmm = FFMIN(ics->tns_max_bands,  ics->max_sfb);
> +    int w, filt, m, i, ib;
> +    int bottom, top, order, start, end, size, inc;
> +    float tmp;
> +    float lpc[TNS_MAX_ORDER + 1], b[2 * TNS_MAX_ORDER];
> +
> +    for (w = 0; w < ics->num_windows; w++) {
> +        bottom = ics->num_swb;
> +        for (filt = 0; filt < tns->n_filt[w]; filt++) {
> +            top = bottom;
> +            bottom = FFMAX(                  0, top - tns->length[w][filt]);

> +            order  = FFMIN(tns->order[w][filt], TNS_MAX_ORDER);

useless?


> +            if (order == 0)
> +                continue;
> +

> +            // tns_decode_coef
> +            lpc[0] = 1;
> +            for (m = 1; m <= order; m++) {
> +                lpc[m] = tns->tmp2_map[w][filt][tns->coef[w][filt][m - 1]];
> +                for (i = 1; i < m; i++)
> +                    b[i] = lpc[i] + lpc[m] * lpc[m-i];
> +                for (i = 1; i < m; i++)
> +                    lpc[i] = b[i];
> +            }

looks a little like eval_coefs from ra144.c
but later is fixedpoint, so this is more a random comment than anything


> +
> +            start = ics->swb_offset[FFMIN(bottom, mmm)];
> +            end   = ics->swb_offset[FFMIN(   top, mmm)];
> +            if ((size = end - start) <= 0)
> +                continue;
> +            if (tns->direction[w][filt]) {
> +                inc = -1; start = end - 1;
> +            } else {
> +                inc = 1;
> +            }
> +            start += w * 128;
> +
> +            // ar filter
> +            memset(b, 0, sizeof(b));
> +            ib = 0;

> +            for (m = 0; m < size; m++) {
> +                tmp = coef[start];
> +                if (decode) {
> +                    for (i = 0; i < order; i++)
> +                        tmp -= b[ib + i] * lpc[i + 1];
> +                } else { // encode
> +                    for (i = 0; i < order; i++)
> +                        tmp += b[i]      * lpc[i + 1];
> +                }
> +                if (--ib < 0)
> +                    ib = order - 1;
> +                b[ib] = b[ib + order] = tmp;
> +                coef[start] = tmp;
> +                start += inc;
> +            }

decode is always 1
b is not truly needed, coef[] can be used i its place
also this is likely relevant to overal codec speed so it
should be written more with speed than compactness in mind

[...]

> @@ -232,6 +245,14 @@
>      /** @} */
>  
>      /**
> +     * @defgroup temporary aligned temporary buffers (We do not want to have these on the stack.)
> +     * @{
> +     */
> +    DECLARE_ALIGNED_16(float, buf_mdct[2048]);
> +    DECLARE_ALIGNED_16(float, revers[1024]);
> +    /** @} */

ok, but if you can reduce the amount of arrays or optimize the imdct
stuff that is welcome ...

[...]
> Index: libavcodec/aacdectab.h
> ===================================================================
> --- libavcodec/aacdectab.h	(revision 14767)
> +++ libavcodec/aacdectab.h	(working copy)
> @@ -156,4 +156,65 @@
>  
>  // @}
>  
> +/* @name tns_max_bands
> + * The maximum number of scalefactor bands on which TNS can operate for the long
> + * and short transforms respectively. The index to these tables is related to
> + * the sample rate of the audio.
> + * @{
> + */
> +static const uint8_t tns_max_bands_1024[] = {
> +    31, 31, 34, 40, 42, 51, 46, 46, 42, 42, 42, 39
> +};
> +
> +static const uint8_t tns_max_bands_128[] = {
> +    9, 9, 10, 14, 14, 14, 14, 14, 14, 14, 14, 14
> +};
> +// @}

ok



> +
> +/* @name tns_tmp2_map
> + * Tables of the tmp2[] arrays of LPC coefficients used for TNS.
> + * The suffix _M_N[] indicate the values of coef_compress and coef_res
> + * respectively.
> + * @{
> + */
> +static const float tns_tmp2_map_1_3[TNS_MAX_ORDER] = {
> +     0.00000000,  0.43388373, -0.64278758, -0.34202015,
> +     0.97492790,  0.78183150, -0.64278758, -0.34202015,
> +    -0.43388373, -0.78183150, -0.64278758, -0.34202015,
> +    -0.78183150, -0.43388373, -0.64278758, -0.34202015,
> +     0.78183150,  0.97492790, -0.64278758, -0.34202015
> +};
> +
> +static const float tns_tmp2_map_0_3[TNS_MAX_ORDER] = {
> +     0.00000000,  0.43388373,  0.78183150,  0.97492790,
> +    -0.98480773, -0.86602539, -0.64278758, -0.34202015,
> +    -0.43388373, -0.78183150, -0.97492790, -0.97492790,
> +    -0.98480773, -0.86602539, -0.64278758, -0.34202015,
> +     0.78183150,  0.97492790,  0.97492790,  0.78183150
> +};
> +
> +static const float tns_tmp2_map_1_4[TNS_MAX_ORDER] = {
> +     0.00000000,  0.20791170,  0.40673664,  0.58778524,
> +    -0.67369562, -0.52643216, -0.36124167, -0.18374951,
> +     0.99452192,  0.95105648,  0.86602539,  0.74314481,
> +    -0.67369562, -0.52643216, -0.36124167, -0.18374951,
> +    -0.20791176, -0.40673670, -0.58778530, -0.74314487
> +};
> +
> +static const float tns_tmp2_map_0_4[TNS_MAX_ORDER] = {
> +     0.00000000,  0.20791170,  0.40673664,  0.58778524,
> +     0.74314481,  0.86602539,  0.95105654,  0.99452192,
> +    -0.99573416, -0.96182561, -0.89516330, -0.79801720,
> +    -0.67369562, -0.52643216, -0.36124167, -0.18374951,
> +    -0.20791176, -0.40673670, -0.58778530, -0.74314487
> +};

iam not sure if the code is correct but i think several of these
elements can never be accessed

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

Good people do not need laws to tell them to act responsibly, while bad
people will find a way around the laws. -- Plato
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