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Fixing the most obvious problems with the VBR code

--- a/libcelt/celt.c

+++ b/libcelt/celt.c

@@ -144,7 +144,7 @@

    st->end = st->mode->effEBands;

    st->vbr_rate_norm = 0;

-   st->vbr_offset = -(64<<BITRES);

+   st->vbr_offset = 0;

    st->force_intra  = 0;

    st->delayedIntra = 1;

    st->tonal_average = 256;

@@ -985,10 +985,12 @@

      target = vbr_rate = M*st->vbr_rate_norm;

+     target = target + st->vbr_offset - ((40*C+20)<<BITRES);

+

      /* Shortblocks get a large boost in bitrate, but since they

         are uncommon long blocks are not greatly affected */

      if (shortBlocks || tf_sum < -2*(st->end-st->start))

-        target*=2;

+        target = 7*target/4;

      else if (tf_sum < -(st->end-st->start))

         target = 3*target/2;

      else if (M > 1)

@@ -996,7 +998,9 @@

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

         so far is added*/

-     target=target+st->vbr_offset+ec_enc_tell(enc, BITRES);

+     target=target+ec_enc_tell(enc, BITRES);

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

+     delta = target - vbr_rate;

      /* Computes the max bit-rate allowed in VBR more to avoid violating the target rate and buffering */

      vbr_bound = vbr_rate;

@@ -1013,10 +1017,8 @@

         alpha = celt_rcp(SHL32(EXTEND32(st->vbr_count+20),16));

      } else

         alpha = QCONST16(.001f,15);

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

-     delta = (celt_int32)target - vbr_rate;

      /* How many bits have we used in excess of what we're allowed */

-     st->vbr_reservoir += delta;

+     st->vbr_reservoir += target - vbr_rate;

      /*printf ("%d\n", st->vbr_reservoir);*/

      /* Compute the offset we need to apply in order to reach the target */

@@ -1320,7 +1322,7 @@

          CELT_MEMSET((char*)&st->ENCODER_RESET_START, 0,

                celt_encoder_get_size(st->mode, st->channels)-

                ((char*)&st->ENCODER_RESET_START - (char*)st));

-         st->vbr_offset = -(64<<BITRES);

+         st->vbr_offset = 0;

          st->delayedIntra = 1;

          st->fold_decision = 1;

          st->tonal_average = QCONST16(1.f,8);