path: root/fdk-aac/libAACenc/src/block_switch.cpp

/* -----------------------------------------------------------------------------
Software License for The Fraunhofer FDK AAC Codec Library for Android

© Copyright  1995 - 2018 Fraunhofer-Gesellschaft zur Förderung der angewandten
Forschung e.V. All rights reserved.

 1.    INTRODUCTION
The Fraunhofer FDK AAC Codec Library for Android ("FDK AAC Codec") is software
that implements the MPEG Advanced Audio Coding ("AAC") encoding and decoding
scheme for digital audio. This FDK AAC Codec software is intended to be used on
a wide variety of Android devices.

AAC's HE-AAC and HE-AAC v2 versions are regarded as today's most efficient
general perceptual audio codecs. AAC-ELD is considered the best-performing
full-bandwidth communications codec by independent studies and is widely
deployed. AAC has been standardized by ISO and IEC as part of the MPEG
specifications.

Patent licenses for necessary patent claims for the FDK AAC Codec (including
those of Fraunhofer) may be obtained through Via Licensing
(www.vialicensing.com) or through the respective patent owners individually for
the purpose of encoding or decoding bit streams in products that are compliant
with the ISO/IEC MPEG audio standards. Please note that most manufacturers of
Android devices already license these patent claims through Via Licensing or
directly from the patent owners, and therefore FDK AAC Codec software may
already be covered under those patent licenses when it is used for those
licensed purposes only.

Commercially-licensed AAC software libraries, including floating-point versions
with enhanced sound quality, are also available from Fraunhofer. Users are
encouraged to check the Fraunhofer website for additional applications
information and documentation.

2.    COPYRIGHT LICENSE

Redistribution and use in source and binary forms, with or without modification,
are permitted without payment of copyright license fees provided that you
satisfy the following conditions:

You must retain the complete text of this software license in redistributions of
the FDK AAC Codec or your modifications thereto in source code form.

You must retain the complete text of this software license in the documentation
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charge copies of the complete source code of the FDK AAC Codec and your
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of the FDK AAC Codec, the term "Fraunhofer FDK AAC Codec Library for Android"
must be replaced by the term "Third-Party Modified Version of the Fraunhofer FDK
AAC Codec Library for Android."

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NO EXPRESS OR IMPLIED LICENSES TO ANY PATENT CLAIMS, including without
limitation the patents of Fraunhofer, ARE GRANTED BY THIS SOFTWARE LICENSE.
Fraunhofer provides no warranty of patent non-infringement with respect to this
software.

You may use this FDK AAC Codec software or modifications thereto only for
purposes that are authorized by appropriate patent licenses.

4.    DISCLAIMER

This FDK AAC Codec software is provided by Fraunhofer on behalf of the copyright
holders and contributors "AS IS" and WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES,
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5.    CONTACT INFORMATION

Fraunhofer Institute for Integrated Circuits IIS
Attention: Audio and Multimedia Departments - FDK AAC LL
Am Wolfsmantel 33
91058 Erlangen, Germany

www.iis.fraunhofer.de/amm
amm-info@iis.fraunhofer.de
----------------------------------------------------------------------------- */

/**************************** AAC encoder library ******************************

   Author(s):   M. Werner, Tobias Chalupka

   Description: Block switching

*******************************************************************************/

/****************** Includes *****************************/

#include "block_switch.h"
#include "genericStds.h"

#define LOWOV_WINDOW _LOWOV_WINDOW

/**************** internal function prototypes ***********/

static FIXP_DBL FDKaacEnc_GetWindowEnergy(const FIXP_DBL in[],
                                          const INT blSwWndIdx);

static void FDKaacEnc_CalcWindowEnergy(
    BLOCK_SWITCHING_CONTROL *RESTRICT blockSwitchingControl, INT windowLen,
    const INT_PCM *pTimeSignal);

/****************** Constants *****************************/
/*                                                LONG         START
 * SHORT         STOP         LOWOV                  */
static const INT blockType2windowShape[2][5] = {
    {SINE_WINDOW, KBD_WINDOW, WRONG_WINDOW, SINE_WINDOW, KBD_WINDOW},  /* LD */
    {KBD_WINDOW, SINE_WINDOW, SINE_WINDOW, KBD_WINDOW, WRONG_WINDOW}}; /* LC */

/* IIR high pass coeffs */

#ifndef SINETABLE_16BIT

static const FIXP_DBL hiPassCoeff[BLOCK_SWITCHING_IIR_LEN] = {
    FL2FXCONST_DBL(-0.5095), FL2FXCONST_DBL(0.7548)};

static const FIXP_DBL accWindowNrgFac =
    FL2FXCONST_DBL(0.3f); /* factor for accumulating filtered window energies */
static const FIXP_DBL oneMinusAccWindowNrgFac = FL2FXCONST_DBL(0.7f);
/* static const float attackRatio = 10.0; */ /* lower ratio limit for attacks */
static const FIXP_DBL invAttackRatio =
    FL2FXCONST_DBL(0.1f); /* inverted lower ratio limit for attacks */

/* The next constants are scaled, because they are used for comparison with
 * scaled values*/
/* minimum energy for attacks */
static const FIXP_DBL minAttackNrg =
    (FL2FXCONST_DBL(1e+6f * NORM_PCM_ENERGY) >>
     BLOCK_SWITCH_ENERGY_SHIFT); /* minimum energy for attacks */

#else

static const FIXP_SGL hiPassCoeff[BLOCK_SWITCHING_IIR_LEN] = {
    FL2FXCONST_SGL(-0.5095), FL2FXCONST_SGL(0.7548)};

static const FIXP_DBL accWindowNrgFac =
    FL2FXCONST_DBL(0.3f); /* factor for accumulating filtered window energies */
static const FIXP_SGL oneMinusAccWindowNrgFac = FL2FXCONST_SGL(0.7f);
/* static const float attackRatio = 10.0; */ /* lower ratio limit for attacks */
static const FIXP_SGL invAttackRatio =
    FL2FXCONST_SGL(0.1f); /* inverted lower ratio limit for attacks */
/* minimum energy for attacks */
static const FIXP_DBL minAttackNrg =
    (FL2FXCONST_DBL(1e+6f * NORM_PCM_ENERGY) >>
     BLOCK_SWITCH_ENERGY_SHIFT); /* minimum energy for attacks */

#endif

/**************** internal function prototypes ***********/

/****************** Routines ****************************/
void FDKaacEnc_InitBlockSwitching(
    BLOCK_SWITCHING_CONTROL *blockSwitchingControl, INT isLowDelay) {
  FDKmemclear(blockSwitchingControl, sizeof(BLOCK_SWITCHING_CONTROL));

  if (isLowDelay) {
    blockSwitchingControl->nBlockSwitchWindows = 4;
    blockSwitchingControl->allowShortFrames = 0;
    blockSwitchingControl->allowLookAhead = 0;
  } else {
    blockSwitchingControl->nBlockSwitchWindows = 8;
    blockSwitchingControl->allowShortFrames = 1;
    blockSwitchingControl->allowLookAhead = 1;
  }

  blockSwitchingControl->noOfGroups = MAX_NO_OF_GROUPS;

  /* Initialize startvalue for blocktype */
  blockSwitchingControl->lastWindowSequence = LONG_WINDOW;
  blockSwitchingControl->windowShape =
      blockType2windowShape[blockSwitchingControl->allowShortFrames]
                           [blockSwitchingControl->lastWindowSequence];
}

static const INT suggestedGroupingTable[TRANS_FAC][MAX_NO_OF_GROUPS] = {
    /* Attack in Window 0 */ {1, 3, 3, 1},
    /* Attack in Window 1 */ {1, 1, 3, 3},
    /* Attack in Window 2 */ {2, 1, 3, 2},
    /* Attack in Window 3 */ {3, 1, 3, 1},
    /* Attack in Window 4 */ {3, 1, 1, 3},
    /* Attack in Window 5 */ {3, 2, 1, 2},
    /* Attack in Window 6 */ {3, 3, 1, 1},
    /* Attack in Window 7 */ {3, 3, 1, 1}};

/* change block type depending on current blocktype and whether there's an
 * attack */
/* assume no look-ahead */
static const INT chgWndSq[2][N_BLOCKTYPES] = {
    /*             LONG WINDOW   START_WINDOW  SHORT_WINDOW  STOP_WINDOW,
       LOWOV_WINDOW, WRONG_WINDOW */
    /*no attack*/ {LONG_WINDOW, STOP_WINDOW, WRONG_WINDOW, LONG_WINDOW,
                   STOP_WINDOW, WRONG_WINDOW},
    /*attack   */ {START_WINDOW, LOWOV_WINDOW, WRONG_WINDOW, START_WINDOW,
                   LOWOV_WINDOW, WRONG_WINDOW}};

/* change block type depending on current blocktype and whether there's an
 * attack */
/* assume look-ahead */
static const INT chgWndSqLkAhd[2][2][N_BLOCKTYPES] = {
    /*attack         LONG WINDOW    START_WINDOW   SHORT_WINDOW   STOP_WINDOW   LOWOV_WINDOW, WRONG_WINDOW */ /* last attack */
    /*no attack*/ {
        {LONG_WINDOW, SHORT_WINDOW, STOP_WINDOW, LONG_WINDOW, WRONG_WINDOW,
         WRONG_WINDOW}, /* no attack   */
        /*attack   */ {START_WINDOW, SHORT_WINDOW, SHORT_WINDOW, START_WINDOW,
                       WRONG_WINDOW, WRONG_WINDOW}}, /* no attack   */
    /*no attack*/ {{LONG_WINDOW, SHORT_WINDOW, SHORT_WINDOW, LONG_WINDOW,
                    WRONG_WINDOW, WRONG_WINDOW}, /* attack      */
                   /*attack   */ {START_WINDOW, SHORT_WINDOW, SHORT_WINDOW,
                                  START_WINDOW, WRONG_WINDOW,
                                  WRONG_WINDOW}} /* attack      */
};

int FDKaacEnc_BlockSwitching(BLOCK_SWITCHING_CONTROL *blockSwitchingControl,
                             const INT granuleLength, const int isLFE,
                             const INT_PCM *pTimeSignal) {
  UINT i;
  FIXP_DBL enM1, enMax;

  UINT nBlockSwitchWindows = blockSwitchingControl->nBlockSwitchWindows;

  /* for LFE : only LONG window allowed */
  if (isLFE) {
    /* case LFE: */
    /* only long blocks, always use sine windows (MPEG2 AAC, MPEG4 AAC) */
    blockSwitchingControl->lastWindowSequence = LONG_WINDOW;
    blockSwitchingControl->windowShape = SINE_WINDOW;
    blockSwitchingControl->noOfGroups = 1;
    blockSwitchingControl->groupLen[0] = 1;

    return (0);
  };

  /* Save current attack index as last attack index */
  blockSwitchingControl->lastattack = blockSwitchingControl->attack;
  blockSwitchingControl->lastAttackIndex = blockSwitchingControl->attackIndex;

  /* Save current window energy as last window energy */
  FDKmemcpy(blockSwitchingControl->windowNrg[0],
            blockSwitchingControl->windowNrg[1],
            sizeof(blockSwitchingControl->windowNrg[0]));
  FDKmemcpy(blockSwitchingControl->windowNrgF[0],
            blockSwitchingControl->windowNrgF[1],
            sizeof(blockSwitchingControl->windowNrgF[0]));

  if (blockSwitchingControl->allowShortFrames) {
    /* Calculate suggested grouping info for the last frame */

    /* Reset grouping info */
    FDKmemclear(blockSwitchingControl->groupLen,
                sizeof(blockSwitchingControl->groupLen));

    /* Set grouping info */
    blockSwitchingControl->noOfGroups = MAX_NO_OF_GROUPS;

    FDKmemcpy(blockSwitchingControl->groupLen,
              suggestedGroupingTable[blockSwitchingControl->lastAttackIndex],
              sizeof(blockSwitchingControl->groupLen));

    if (blockSwitchingControl->attack == TRUE)
      blockSwitchingControl->maxWindowNrg =
          FDKaacEnc_GetWindowEnergy(blockSwitchingControl->windowNrg[0],
                                    blockSwitchingControl->lastAttackIndex);
    else
      blockSwitchingControl->maxWindowNrg = FL2FXCONST_DBL(0.0);
  }

  /* Calculate unfiltered and filtered energies in subwindows and combine to
   * segments */
  FDKaacEnc_CalcWindowEnergy(
      blockSwitchingControl,
      granuleLength >> (nBlockSwitchWindows == 4 ? 2 : 3), pTimeSignal);

  /* now calculate if there is an attack */

  /* reset attack */
  blockSwitchingControl->attack = FALSE;

  /* look for attack */
  enMax = FL2FXCONST_DBL(0.0f);
  enM1 = blockSwitchingControl->windowNrgF[0][nBlockSwitchWindows - 1];

  for (i = 0; i < nBlockSwitchWindows; i++) {
    FIXP_DBL tmp =
        fMultDiv2(oneMinusAccWindowNrgFac, blockSwitchingControl->accWindowNrg);
    blockSwitchingControl->accWindowNrg = fMultAdd(tmp, accWindowNrgFac, enM1);

    if (fMult(blockSwitchingControl->windowNrgF[1][i], invAttackRatio) >
        blockSwitchingControl->accWindowNrg) {
      blockSwitchingControl->attack = TRUE;
      blockSwitchingControl->attackIndex = i;
    }
    enM1 = blockSwitchingControl->windowNrgF[1][i];
    enMax = fixMax(enMax, enM1);
  }

  if (enMax < minAttackNrg) blockSwitchingControl->attack = FALSE;

  /* Check if attack spreads over frame border */
  if ((blockSwitchingControl->attack == FALSE) &&
      (blockSwitchingControl->lastattack == TRUE)) {
    /* if attack is in last window repeat SHORT_WINDOW */
    if (((blockSwitchingControl->windowNrgF[0][nBlockSwitchWindows - 1] >> 4) >
         fMult((FIXP_DBL)(10 << (DFRACT_BITS - 1 - 4)),
               blockSwitchingControl->windowNrgF[1][1])) &&
        (blockSwitchingControl->lastAttackIndex ==
         (INT)nBlockSwitchWindows - 1)) {
      blockSwitchingControl->attack = TRUE;
      blockSwitchingControl->attackIndex = 0;
    }
  }

  if (blockSwitchingControl->allowLookAhead) {
    blockSwitchingControl->lastWindowSequence =
        chgWndSqLkAhd[blockSwitchingControl->lastattack]
                     [blockSwitchingControl->attack]
                     [blockSwitchingControl->lastWindowSequence];
  } else {
    /* Low Delay */
    blockSwitchingControl->lastWindowSequence =
        chgWndSq[blockSwitchingControl->attack]
                [blockSwitchingControl->lastWindowSequence];
  }

  /* update window shape */
  blockSwitchingControl->windowShape =
      blockType2windowShape[blockSwitchingControl->allowShortFrames]
                           [blockSwitchingControl->lastWindowSequence];

  return (0);
}

static FIXP_DBL FDKaacEnc_GetWindowEnergy(const FIXP_DBL in[],
                                          const INT blSwWndIdx) {
  /* For coherency, change FDKaacEnc_GetWindowEnergy() to calcluate the energy
     for a block switching analysis windows, not for a short block. The same is
     done FDKaacEnc_CalcWindowEnergy(). The result of
     FDKaacEnc_GetWindowEnergy() is used for a comparision of the max energy of
     left/right channel. */

  return in[blSwWndIdx];
}

static void FDKaacEnc_CalcWindowEnergy(
    BLOCK_SWITCHING_CONTROL *RESTRICT blockSwitchingControl, INT windowLen,
    const INT_PCM *pTimeSignal) {
  INT i;
  UINT w;

#ifndef SINETABLE_16BIT
  const FIXP_DBL hiPassCoeff0 = hiPassCoeff[0];
  const FIXP_DBL hiPassCoeff1 = hiPassCoeff[1];
#else
  const FIXP_SGL hiPassCoeff0 = hiPassCoeff[0];
  const FIXP_SGL hiPassCoeff1 = hiPassCoeff[1];
#endif

  FIXP_DBL temp_iirState0 = blockSwitchingControl->iirStates[0];
  FIXP_DBL temp_iirState1 = blockSwitchingControl->iirStates[1];

  /* sum up scalarproduct of timesignal as windowed Energies */
  for (w = 0; w < blockSwitchingControl->nBlockSwitchWindows; w++) {
    ULONG temp_windowNrg = 0x0;
    ULONG temp_windowNrgF = 0x0;

    /* windowNrg = sum(timesample^2) */
    for (i = 0; i < windowLen; i++) {
      FIXP_DBL tempUnfiltered, t1, t2;
      /* tempUnfiltered is scaled with 1 to prevent overflows during calculation
       * of tempFiltred */
#if SAMPLE_BITS == DFRACT_BITS
      tempUnfiltered = (FIXP_DBL)*pTimeSignal++ >> 1;
#else
      tempUnfiltered = (FIXP_DBL)*pTimeSignal++
                       << (DFRACT_BITS - SAMPLE_BITS - 1);
#endif
      t1 = fMultDiv2(hiPassCoeff1, tempUnfiltered - temp_iirState0);
      t2 = fMultDiv2(hiPassCoeff0, temp_iirState1);
      temp_iirState0 = tempUnfiltered;
      temp_iirState1 = (t1 - t2) << 1;

      temp_windowNrg += (LONG)fPow2Div2(temp_iirState0) >>
                        (BLOCK_SWITCH_ENERGY_SHIFT - 1 - 2);
      temp_windowNrgF += (LONG)fPow2Div2(temp_iirState1) >>
                         (BLOCK_SWITCH_ENERGY_SHIFT - 1 - 2);
    }
    blockSwitchingControl->windowNrg[1][w] =
        (LONG)fMin(temp_windowNrg, (UINT)MAXVAL_DBL);
    blockSwitchingControl->windowNrgF[1][w] =
        (LONG)fMin(temp_windowNrgF, (UINT)MAXVAL_DBL);
  }
  blockSwitchingControl->iirStates[0] = temp_iirState0;
  blockSwitchingControl->iirStates[1] = temp_iirState1;
}

static const UCHAR synchronizedBlockTypeTable[5][5] = {
    /*                  LONG_WINDOW   START_WINDOW  SHORT_WINDOW  STOP_WINDOW
       LOWOV_WINDOW*/
    /* LONG_WINDOW  */ {LONG_WINDOW, START_WINDOW, SHORT_WINDOW, STOP_WINDOW,
                        LOWOV_WINDOW},
    /* START_WINDOW */
    {START_WINDOW, START_WINDOW, SHORT_WINDOW, SHORT_WINDOW, LOWOV_WINDOW},
    /* SHORT_WINDOW */
    {SHORT_WINDOW, SHORT_WINDOW, SHORT_WINDOW, SHORT_WINDOW, WRONG_WINDOW},
    /* STOP_WINDOW  */
    {STOP_WINDOW, SHORT_WINDOW, SHORT_WINDOW, STOP_WINDOW, LOWOV_WINDOW},
    /* LOWOV_WINDOW */
    {LOWOV_WINDOW, LOWOV_WINDOW, WRONG_WINDOW, LOWOV_WINDOW, LOWOV_WINDOW},
};

int FDKaacEnc_SyncBlockSwitching(
    BLOCK_SWITCHING_CONTROL *blockSwitchingControlLeft,
    BLOCK_SWITCHING_CONTROL *blockSwitchingControlRight, const INT nChannels,
    const INT commonWindow) {
  UCHAR patchType = LONG_WINDOW;

  if (nChannels == 2 && commonWindow == TRUE) {
    /* could be better with a channel loop (need a handle to psy_data) */
    /* get suggested Block Types and synchronize */
    patchType = synchronizedBlockTypeTable[patchType][blockSwitchingControlLeft
                                                          ->lastWindowSequence];
    patchType = synchronizedBlockTypeTable[patchType][blockSwitchingControlRight
                                                          ->lastWindowSequence];

    /* sanity check (no change from low overlap window to short winow and vice
     * versa) */
    if (patchType == WRONG_WINDOW) return -1; /* mixed up AAC-LC and AAC-LD */

    /* Set synchronized Blocktype */
    blockSwitchingControlLeft->lastWindowSequence = patchType;
    blockSwitchingControlRight->lastWindowSequence = patchType;

    /* update window shape */
    blockSwitchingControlLeft->windowShape =
        blockType2windowShape[blockSwitchingControlLeft->allowShortFrames]
                             [blockSwitchingControlLeft->lastWindowSequence];
    blockSwitchingControlRight->windowShape =
        blockType2windowShape[blockSwitchingControlLeft->allowShortFrames]
                             [blockSwitchingControlRight->lastWindowSequence];
  }

  if (blockSwitchingControlLeft->allowShortFrames) {
    int i;

    if (nChannels == 2) {
      if (commonWindow == TRUE) {
        /* Synchronize grouping info */
        int windowSequenceLeftOld =
            blockSwitchingControlLeft->lastWindowSequence;
        int windowSequenceRightOld =
            blockSwitchingControlRight->lastWindowSequence;

        /* Long Blocks */
        if (patchType != SHORT_WINDOW) {
          /* Set grouping info */
          blockSwitchingControlLeft->noOfGroups = 1;
          blockSwitchingControlRight->noOfGroups = 1;
          blockSwitchingControlLeft->groupLen[0] = 1;
          blockSwitchingControlRight->groupLen[0] = 1;

          for (i = 1; i < MAX_NO_OF_GROUPS; i++) {
            blockSwitchingControlLeft->groupLen[i] = 0;
            blockSwitchingControlRight->groupLen[i] = 0;
          }
        }

        /* Short Blocks */
        else {
          /* in case all two channels were detected as short-blocks before
           * syncing, use the grouping of channel with higher maxWindowNrg */
          if ((windowSequenceLeftOld == SHORT_WINDOW) &&
              (windowSequenceRightOld == SHORT_WINDOW)) {
            if (blockSwitchingControlLeft->maxWindowNrg >
                blockSwitchingControlRight->maxWindowNrg) {
              /* Left Channel wins */
              blockSwitchingControlRight->noOfGroups =
                  blockSwitchingControlLeft->noOfGroups;
              for (i = 0; i < MAX_NO_OF_GROUPS; i++) {
                blockSwitchingControlRight->groupLen[i] =
                    blockSwitchingControlLeft->groupLen[i];
              }
            } else {
              /* Right Channel wins */
              blockSwitchingControlLeft->noOfGroups =
                  blockSwitchingControlRight->noOfGroups;
              for (i = 0; i < MAX_NO_OF_GROUPS; i++) {
                blockSwitchingControlLeft->groupLen[i] =
                    blockSwitchingControlRight->groupLen[i];
              }
            }
          } else if ((windowSequenceLeftOld == SHORT_WINDOW) &&
                     (windowSequenceRightOld != SHORT_WINDOW)) {
            /* else use grouping of short-block channel */
            blockSwitchingControlRight->noOfGroups =
                blockSwitchingControlLeft->noOfGroups;
            for (i = 0; i < MAX_NO_OF_GROUPS; i++) {
              blockSwitchingControlRight->groupLen[i] =
                  blockSwitchingControlLeft->groupLen[i];
            }
          } else if ((windowSequenceRightOld == SHORT_WINDOW) &&
                     (windowSequenceLeftOld != SHORT_WINDOW)) {
            blockSwitchingControlLeft->noOfGroups =
                blockSwitchingControlRight->noOfGroups;
            for (i = 0; i < MAX_NO_OF_GROUPS; i++) {
              blockSwitchingControlLeft->groupLen[i] =
                  blockSwitchingControlRight->groupLen[i];
            }
          } else {
            /* syncing a start and stop window ... */
            blockSwitchingControlLeft->noOfGroups =
                blockSwitchingControlRight->noOfGroups = 2;
            blockSwitchingControlLeft->groupLen[0] =
                blockSwitchingControlRight->groupLen[0] = 4;
            blockSwitchingControlLeft->groupLen[1] =
                blockSwitchingControlRight->groupLen[1] = 4;
          }
        } /* Short Blocks */
      } else {
        /* stereo, no common window */
        if (blockSwitchingControlLeft->lastWindowSequence != SHORT_WINDOW) {
          blockSwitchingControlLeft->noOfGroups = 1;
          blockSwitchingControlLeft->groupLen[0] = 1;
          for (i = 1; i < MAX_NO_OF_GROUPS; i++) {
            blockSwitchingControlLeft->groupLen[i] = 0;
          }
        }
        if (blockSwitchingControlRight->lastWindowSequence != SHORT_WINDOW) {
          blockSwitchingControlRight->noOfGroups = 1;
          blockSwitchingControlRight->groupLen[0] = 1;
          for (i = 1; i < MAX_NO_OF_GROUPS; i++) {
            blockSwitchingControlRight->groupLen[i] = 0;
          }
        }
      } /* common window */
    } else {
      /* Mono */
      if (blockSwitchingControlLeft->lastWindowSequence != SHORT_WINDOW) {
        blockSwitchingControlLeft->noOfGroups = 1;
        blockSwitchingControlLeft->groupLen[0] = 1;

        for (i = 1; i < MAX_NO_OF_GROUPS; i++) {
          blockSwitchingControlLeft->groupLen[i] = 0;
        }
      }
    }
  } /* allowShortFrames */

  /* Translate LOWOV_WINDOW block type to a meaningful window shape. */
  if (!blockSwitchingControlLeft->allowShortFrames) {
    if (blockSwitchingControlLeft->lastWindowSequence != LONG_WINDOW &&
        blockSwitchingControlLeft->lastWindowSequence != STOP_WINDOW) {
      blockSwitchingControlLeft->lastWindowSequence = LONG_WINDOW;
      blockSwitchingControlLeft->windowShape = LOL_WINDOW;
    }
  }
  if (nChannels == 2) {
    if (!blockSwitchingControlRight->allowShortFrames) {
      if (blockSwitchingControlRight->lastWindowSequence != LONG_WINDOW &&
          blockSwitchingControlRight->lastWindowSequence != STOP_WINDOW) {
        blockSwitchingControlRight->lastWindowSequence = LONG_WINDOW;
        blockSwitchingControlRight->windowShape = LOL_WINDOW;
      }
    }
  }

  return 0;
}