Add spectral extension to the E-AC-3 decoder.

Original patch by Justin, updated and resubmitted by
Christophe Gisquet, christophe D gisquet A gmail

Originally committed as revision 22734 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 95 insertions, 10 deletions

diff --git a/libavcodec/eac3dec.c b/libavcodec/eac3dec.c
index 3784ccfb1d..52d15c83f8 100644
--- a/libavcodec/eac3dec.c
+++ b/libavcodec/eac3dec.c
@@ -23,10 +23,6 @@
 /*
  * There are several features of E-AC-3 that this decoder does not yet support.
  *
- * Spectral Extension
- *     There is a patch to get this working for the two samples we have that
- *     use it, but it needs some minor changes in order to be accepted.
- *
  * Enhanced Coupling
  *     No known samples exist.  If any ever surface, this feature should not be
  *     too difficult to implement.
@@ -67,6 +63,95 @@ typedef enum {
 
 #define EAC3_SR_CODE_REDUCED  3
 
+void ff_eac3_apply_spectral_extension(AC3DecodeContext *s)
+{
+    int bin, bnd, ch, i;
+    uint8_t wrapflag[SPX_MAX_BANDS]={1,0,}, num_copy_sections, copy_sizes[SPX_MAX_BANDS];
+    float rms_energy[SPX_MAX_BANDS];
+
+    /* Set copy index mapping table. Set wrap flags to apply a notch filter at
+       wrap points later on. */
+    bin = s->spx_dst_start_freq;
+    num_copy_sections = 0;
+    for (bnd = 0; bnd < s->num_spx_bands; bnd++) {
+        int copysize;
+        int bandsize = s->spx_band_sizes[bnd];
+        if (bin + bandsize > s->spx_src_start_freq) {
+            copy_sizes[num_copy_sections++] = bin - s->spx_dst_start_freq;
+            bin = s->spx_dst_start_freq;
+            wrapflag[bnd] = 1;
+        }
+        for (i = 0; i < bandsize; i += copysize) {
+            if (bin == s->spx_src_start_freq) {
+                copy_sizes[num_copy_sections++] = bin - s->spx_dst_start_freq;
+                bin = s->spx_dst_start_freq;
+            }
+            copysize = FFMIN(bandsize - i, s->spx_src_start_freq - bin);
+            bin += copysize;
+        }
+    }
+    copy_sizes[num_copy_sections++] = bin - s->spx_dst_start_freq;
+
+    for (ch = 1; ch <= s->fbw_channels; ch++) {
+        if (!s->channel_uses_spx[ch])
+            continue;
+
+        /* Copy coeffs from normal bands to extension bands */
+        bin = s->spx_src_start_freq;
+        for (i = 0; i < num_copy_sections; i++) {
+            memcpy(&s->transform_coeffs[ch][bin],
+                   &s->transform_coeffs[ch][s->spx_dst_start_freq],
+                   copy_sizes[i]*sizeof(float));
+            bin += copy_sizes[i];
+        }
+
+        /* Calculate RMS energy for each SPX band. */
+        bin = s->spx_src_start_freq;
+        for (bnd = 0; bnd < s->num_spx_bands; bnd++) {
+            int bandsize = s->spx_band_sizes[bnd];
+            float accum = 0.0f;
+            for (i = 0; i < bandsize; i++) {
+                float coeff = s->transform_coeffs[ch][bin++];
+                accum += coeff * coeff;
+            }
+            rms_energy[bnd] = sqrtf(accum / bandsize);
+        }
+
+        /* Apply a notch filter at transitions between normal and extension
+           bands and at all wrap points. */
+        if (s->spx_atten_code[ch] >= 0) {
+            const float *atten_tab = ff_eac3_spx_atten_tab[s->spx_atten_code[ch]];
+            bin = s->spx_src_start_freq - 2;
+            for (bnd = 0; bnd < s->num_spx_bands; bnd++) {
+                if (wrapflag[bnd]) {
+                    float *coeffs = &s->transform_coeffs[ch][bin];
+                    coeffs[0] *= atten_tab[0];
+                    coeffs[1] *= atten_tab[1];
+                    coeffs[2] *= atten_tab[2];
+                    coeffs[3] *= atten_tab[1];
+                    coeffs[4] *= atten_tab[0];
+                }
+                bin += s->spx_band_sizes[bnd];
+            }
+        }
+
+        /* Apply noise-blended coefficient scaling based on previously
+           calculated RMS energy, blending factors, and SPX coordinates for
+           each band. */
+        bin = s->spx_src_start_freq;
+        for (bnd = 0; bnd < s->num_spx_bands; bnd++) {
+            float nscale = s->spx_noise_blend[ch][bnd] * rms_energy[bnd] * (1.0f/(1<<31));
+            float sscale = s->spx_signal_blend[ch][bnd];
+            for (i = 0; i < s->spx_band_sizes[bnd]; i++) {
+                float noise  = nscale * (int32_t)av_lfg_get(&s->dith_state);
+                s->transform_coeffs[ch][bin]   *= sscale;
+                s->transform_coeffs[ch][bin++] += noise;
+            }
+        }
+    }
+}
+
+
 /** lrint(M_SQRT2*cos(2*M_PI/12)*(1<<23)) */
 #define COEFF_0 10273905LL
 
@@ -492,12 +577,11 @@ int ff_eac3_parse_header(AC3DecodeContext *s)
     }
 
     /* spectral extension attenuation data */
-    if (parse_spx_atten_data) {
-        av_log_missing_feature(s->avctx, "Spectral extension attenuation", 1);
-        for (ch = 1; ch <= s->fbw_channels; ch++) {
-            if (get_bits1(gbc)) { // channel has spx attenuation
-                skip_bits(gbc, 5); // skip spx attenuation code
-            }
+    for (ch = 1; ch <= s->fbw_channels; ch++) {
+        if (parse_spx_atten_data && get_bits1(gbc)) {
+            s->spx_atten_code[ch] = get_bits(gbc, 5);
+        } else {
+            s->spx_atten_code[ch] = -1;
         }
     }
 
@@ -514,6 +598,7 @@ int ff_eac3_parse_header(AC3DecodeContext *s)
 
     /* syntax state initialization */
     for (ch = 1; ch <= s->fbw_channels; ch++) {
+        s->first_spx_coords[ch] = 1;
         s->first_cpl_coords[ch] = 1;
     }
     s->first_cpl_leak = 1;