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Fixes for silence handling in VBR mode, plus an encoder/decoder desync triggered by silent frames.

--- a/libcelt/celt.c

+++ b/libcelt/celt.c

@@ -927,6 +927,14 @@

       ec_enc_bit_logp(enc, silence, 15);

       if (silence)

       {

+         /*In VBR mode there is no need to send more than the minimum. */

+         if (vbr_rate>0)

+         {

+            effectiveBytes=nbCompressedBytes=nbFilledBytes+2;

+            total_bits=nbCompressedBytes*8;

+            nbAvailableBytes=2;

+            ec_byte_shrink(&buf, nbCompressedBytes);

+         }

          /* Pretend we've filled all the remaining bits with zeros

             (that's what the initialiser did anyway) */

          tell = nbCompressedBytes*8;

@@ -1192,8 +1200,6 @@

      /* The current offset is removed from the target and the space used

         so far is added*/

      target=target+tell;

-     /* By how much did we "miss" the target on that frame */

-     delta = target - vbr_rate;

      /* In VBR mode the frame size must not be reduced so much that it would

          result in the encoder running out of bits.

@@ -1205,6 +1211,15 @@

      nbAvailableBytes = IMAX(min_allowed,nbAvailableBytes);

      nbAvailableBytes = IMIN(nbCompressedBytes,nbAvailableBytes+nbFilledBytes) - nbFilledBytes;

+     if(silence)

+     {

+       nbAvailableBytes = 2;

+       target = 2*8<<BITRES;

+     }

+

+     /* By how much did we "miss" the target on that frame */

+     delta = target - vbr_rate;

+

      target=nbAvailableBytes<<(BITRES+3);

      if (st->vbr_count < 970)

@@ -1227,16 +1242,15 @@

      {

         /* We're under the min value -- increase rate */

         int adjust = (-st->vbr_reservoir)/(8<<BITRES);

-        nbAvailableBytes += adjust;

+        /* Unless we're just coding silence */

+        nbAvailableBytes += silence?0:adjust;

         st->vbr_reservoir = 0;

         /*printf ("+%d\n", adjust);*/

      }

      nbCompressedBytes = IMIN(nbCompressedBytes,nbAvailableBytes+nbFilledBytes);

-

      /* This moves the raw bits to take into account the new compressed size */

      ec_byte_shrink(&buf, nbCompressedBytes);

    }

-

    if (C==2)

    {

       int effectiveRate;

@@ -1307,6 +1321,15 @@

    }

    quant_energy_finalise(st->mode, st->start, st->end, oldBandE, error, fine_quant, fine_priority, nbCompressedBytes*8-ec_enc_tell(enc, 0), enc, C);

+   if (silence)

+   {

+      for (i=0;i<C*st->mode->nbEBands;i++)

+      {

+         bandE[i] = 0;

+         oldBandE[i] = -QCONST16(28.f,DB_SHIFT);

+      }

+   }

+

 #ifdef RESYNTH

    /* Re-synthesis of the coded audio if required */

    if (resynth)

@@ -1316,14 +1339,6 @@

       log2Amp(st->mode, st->start, st->end, bandE, oldBandE, C);

-      if (silence)

-      {

-         for (i=0;i<C*st->mode->nbEBands;i++)

-         {

-            bandE[i] = 0;

-            oldBandE[i] = -QCONST16(9.f,DB_SHIFT);

-         }

-      }

 #ifdef MEASURE_NORM_MSE

       measure_norm_mse(st->mode, X, X0, bandE, bandE0, M, N, C);

 #endif

@@ -2154,7 +2169,7 @@

       for (i=0;i<C*st->mode->nbEBands;i++)

       {

          bandE[i] = 0;

-         oldBandE[i] = -QCONST16(9.f,DB_SHIFT);

+         oldBandE[i] = -QCONST16(28.f,DB_SHIFT);

       }

    }

    /* Synthesis */