[Opus] Update to v1.2.1

third_party/opus/src/celt/rate.c

 /* Copyright (c) 2007-2008 CSIRO
    Copyright (c) 2007-2009 Xiph.Org Foundation
    Written by Jean-Marc Valin */
 /*
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:
 
    - Redistributions of source code must retain the above copyright
    notice, this list of conditions and the following disclaimer.
@@ skipping 330 matching lines @@
       /*Only code a skip decision if we're above the threshold for this band.
         Otherwise it is force-skipped.
         This ensures that we have enough bits to code the skip flag.*/
       if (band_bits >= IMAX(thresh[j], alloc_floor+(1<<BITRES)))
       {
          if (encode)
          {
             /*This if() block is the only part of the allocation function that
                is not a mandatory part of the bitstream: any bands we choose to
                skip here must be explicitly signaled.*/
-            /*Choose a threshold with some hysteresis to keep bands from
-               fluctuating in and out.*/
+            int depth_threshold;
+            /*We choose a threshold with some hysteresis to keep bands from
+               fluctuating in and out, but we try not to fold below a certain point. */
+            if (codedBands > 17)
+               depth_threshold = j<prev ? 7 : 9;
+            else
+               depth_threshold = 0;
 #ifdef FUZZING
             if ((rand()&0x1) == 0)
 #else
-            if (codedBands<=start+2 || (band_bits > ((j<prev?7:9)*band_width<<LM<<BITRES)>>4 && j<=signalBandwidth))
+            if (codedBands<=start+2 || (band_bits > (depth_threshold*band_width<<LM<<BITRES)>>4 && j<=signalBandwidth))
 #endif
             {
                ec_enc_bit_logp(ec, 1, 1);
                break;
             }
             ec_enc_bit_logp(ec, 0, 1);
          } else if (ec_dec_bit_logp(ec, 1)) {
             break;
          }
          /*We used a bit to skip this band.*/
@@ skipping 263 matching lines @@
       bits1[j] = bits1j;
       bits2[j] = bits2j;
    }
    codedBands = interp_bits2pulses(m, start, end, skip_start, bits1, bits2, thresh, cap,
          total, balance, skip_rsv, intensity, intensity_rsv, dual_stereo, dual_stereo_rsv,
          pulses, ebits, fine_priority, C, LM, ec, encode, prev, signalBandwidth);
    RESTORE_STACK;
    return codedBands;
 }