AC-3 decoder, soc revision 69, Aug 31 07:12:56 2006 UTC by cloud9

Fix the bugs:
1. The quality of output because of incorrect windowing coefficients.
New code for window generation.

2. Dynrng values were reset where dynrng value is present in the first block,
but not in the subsequent block.

Originally committed as revision 9667 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/ac3dec.c

@@ -151,6 +151,8 @@ typedef struct {
     int      nfchans;
     int      lfeon;
 
+    float    dynrng;
+    float    dynrng2;
     float    chcoeffs[6];
     float    cplco[5][18];
     int      ncplbnd;
@@ -176,6 +178,7 @@ typedef struct {
     DECLARE_ALIGNED_16(float, delay[MAX_CHANNELS][BLOCK_SIZE]);
     DECLARE_ALIGNED_16(float, tmp_imdct[BLOCK_SIZE]);
     DECLARE_ALIGNED_16(float, tmp_output[BLOCK_SIZE * 2]);
+    DECLARE_ALIGNED_16(float, window[BLOCK_SIZE]);
 
     /* Miscellaneous. */
     GetBitContext gb;
@@ -231,49 +234,29 @@ static inline int16_t dither_int16(dither_state *state)
 
 /* END Mersenne Twister */
 
-/**
- * Generate a Kaiser Window.
- */
-static void
-k_window_init(int alpha, float *window, int n, int iter)
-{
-    int j, k;
-    float a, x;
-    a = alpha * M_PI / n;
-    a = a*a;
-    for(k=0; k<n; k++) {
-        x = k * (n - k) * a;
-        window[k] = 1.0;
-        for(j=iter; j>0; j--) {
-            window[k] = (window[k] * x / (j*j)) + 1.0;
-        }
-    }
-}
-
 /**
  * Generate a Kaiser-Bessel Derived Window.
- * @param alpha  determines window shape
- * @param window array to fill with window values
- * @param n      length of the window
- * @param iter   number of iterations to use in BesselI0
  */
 static void
-kbd_window_init(int alpha, float *window, int n, int iter)
+ac3_window_init(float *window)
 {
-    int k, n2;
-    float *kwindow;
-
-    n2 = n >> 1;
-    kwindow = &window[n2];
-    k_window_init(alpha, kwindow, n2, iter);
-    window[0] = kwindow[0];
-    for(k=1; k<n2; k++) {
-        window[k] = window[k-1] + kwindow[k];
-    }
-    for(k=0; k<n2; k++) {
-        window[k] = sqrt(window[k] / (window[n2-1]+1));
-        window[n-1-k] = window[k];
-    }
+   int i, j;
+   double sum = 0.0, bessel, tmp;
+   double local_window[256];
+   double alpha2 = (5.0 * M_PI / 256.0) * (5.0 * M_PI / 256.0);
+
+   for (i = 0; i < 256; i++) {
+       tmp = i * (256 - i) * alpha2;
+       bessel = 1.0;
+       for (j = 100; j > 0; j--) /* defaul to 100 iterations */
+           bessel = bessel * tmp / (j * j) + 1;
+       sum += bessel;
+       local_window[i] = sum;
+   }
+
+   sum++;
+   for (i = 0; i < 256; i++)
+       window[i] = sqrt(local_window[i] / sum);
 }
 
 static void generate_quantizers_table(int16_t quantizers[], int level, int length)
@@ -385,9 +368,6 @@ static void ac3_tables_init(void)
 
     //for level-15 quantizers
     generate_quantizers_table(l15_quantizers, 15, 15);
-
-    /* Kaiser-Bessel derived window. */
-    kbd_window_init(5, window, 256, 100);
 }
 
 
@@ -398,6 +378,8 @@ static int ac3_decode_init(AVCodecContext *avctx)
     ac3_tables_init();
     ff_mdct_init(&ctx->imdct_256, 8, 1);
     ff_mdct_init(&ctx->imdct_512, 9, 1);
+    /* Kaiser-Bessel derived window. */
+    ac3_window_init(ctx->window);
     dsputil_init(&ctx->dsp, avctx);
     dither_seed(&ctx->dith_state, 0);
 
@@ -469,6 +451,8 @@ static void ac3_parse_bsi(AC3DecodeContext *ctx)
         ctx->deltbae[i] = AC3_DBASTR_NONE;
         ctx->deltnseg[i] = 0;
     }
+    ctx->dynrng = 1.0;
+    ctx->dynrng2 = 1.0;
 
     ctx->acmod = get_bits(gb, 3);
     ctx->nfchans = nfchans_tbl[ctx->acmod];
@@ -1075,6 +1059,15 @@ static void get_downmix_coeffs(AC3DecodeContext *ctx)
     float clev = clevs[ctx->cmixlev];
     float slev = slevs[ctx->surmixlev];
     float nf = 1.0; //normalization factor for downmix coeffs
+    int i;
+
+    if (!ctx->acmod) {
+        ctx->chcoeffs[0] = 2 * ctx->dynrng;
+        ctx->chcoeffs[1] = 2 * ctx->dynrng2;
+    } else {
+        for (i = 0; i < ctx->nfchans; i++)
+            ctx->chcoeffs[i] = 2 * ctx->dynrng;
+    }
 
     if (to == AC3_OUTPUT_UNMODIFIED)
         return;
@@ -1579,9 +1572,9 @@ static void do_imdct_256(AC3DecodeContext *ctx, int chindex)
     ff_imdct_calc(&ctx->imdct_256, ctx->tmp_output + 256, x2, ctx->tmp_imdct);
 
     ptr = ctx->output[chindex];
-    ctx->dsp.vector_fmul_add_add(ptr, ctx->tmp_output, window, ctx->delay[chindex], 384, BLOCK_SIZE, 1);
+    ctx->dsp.vector_fmul_add_add(ptr, ctx->tmp_output, ctx->window, ctx->delay[chindex], 384, BLOCK_SIZE, 1);
     ptr = ctx->delay[chindex];
-    ctx->dsp.vector_fmul_reverse(ptr, ctx->tmp_output + 256, window, BLOCK_SIZE);
+    ctx->dsp.vector_fmul_reverse(ptr, ctx->tmp_output + 256, ctx->window, BLOCK_SIZE);
 }
 
 static void do_imdct_512(AC3DecodeContext *ctx, int chindex)
@@ -1591,9 +1584,9 @@ static void do_imdct_512(AC3DecodeContext *ctx, int chindex)
     ff_imdct_calc(&ctx->imdct_512, ctx->tmp_output,
             ctx->transform_coeffs[chindex], ctx->tmp_imdct);
     ptr = ctx->output[chindex];
-    ctx->dsp.vector_fmul_add_add(ptr, ctx->tmp_output, window, ctx->delay[chindex], 384, BLOCK_SIZE, 1);
+    ctx->dsp.vector_fmul_add_add(ptr, ctx->tmp_output, ctx->window, ctx->delay[chindex], 384, BLOCK_SIZE, 1);
     ptr = ctx->delay[chindex];
-    ctx->dsp.vector_fmul_reverse(ptr, ctx->tmp_output + 256, window, BLOCK_SIZE);
+    ctx->dsp.vector_fmul_reverse(ptr, ctx->tmp_output + 256, ctx->window, BLOCK_SIZE);
 }
 
 static inline void do_imdct(AC3DecodeContext *ctx)
@@ -1623,9 +1616,6 @@ static int ac3_parse_audio_block(AC3DecodeContext * ctx)
     int mstrcplco, cplcoexp, cplcomant;
     int dynrng, chbwcod, ngrps, cplabsexp, skipl;
 
-    for (i = 0; i < 5; i++)
-        ctx->chcoeffs[i] = 2.0;
-
     ctx->blksw = 0;
     for (i = 0; i < nfchans; i++) /*block switch flag */
         ctx->blksw |= get_bits1(gb) << i;
@@ -1636,15 +1626,12 @@ static int ac3_parse_audio_block(AC3DecodeContext * ctx)
 
     if (get_bits1(gb)) { /* dynamic range */
         dynrng = get_sbits(gb, 8);
-        drange = ((((dynrng & 0x1f) | 0x20) << 13) * scale_factors[3 - (dynrng >> 5)]);
-        for (i = 0; i < nfchans; i++)
-            ctx->chcoeffs[i] *= drange;
+        ctx->dynrng = ((((dynrng & 0x1f) | 0x20) << 13) * scale_factors[3 - (dynrng >> 5)]);
     }
 
     if (acmod == 0x00 && get_bits1(gb)) { /* dynamic range 1+1 mode */
         dynrng = get_sbits(gb, 8);
-        drange = ((((dynrng & 0x1f) | 0x20) << 13) * scale_factors[3 - (dynrng >> 5)]);
-        ctx->chcoeffs[1] *= drange;
+        ctx->dynrng2 = ((((dynrng & 0x1f) | 0x20) << 13) * scale_factors[3 - (dynrng >> 5)]);
     }
 
     get_downmix_coeffs(ctx);