path: root/libAACenc/src/block_switch.cpp

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

� Copyright  1995 - 2012 Fraunhofer-Gesellschaft zur F�rderung 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 and/or other materials
provided with redistributions of the FDK AAC Codec or your modifications thereto in binary form.
You must make available free of charge copies of the complete source code of the FDK AAC Codec and your
modifications thereto to recipients of copies in binary form.

The name of Fraunhofer may not be used to endorse or promote products derived from this library without
prior written permission.

You may not charge copyright license fees for anyone to use, copy or distribute the FDK AAC Codec
software or your modifications thereto.

Your modified versions of the FDK AAC Codec must carry prominent notices stating that you changed the software
and the date of any change. For modified versions 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."

3.    NO PATENT LICENSE

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, including but not limited to the implied warranties
of merchantability and fitness for a particular purpose. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
CONTRIBUTORS BE LIABLE for any direct, indirect, incidental, special, exemplary, or consequential damages,
including but not limited to procurement of substitute goods or services; loss of use, data, or profits,
or business interruption, however caused and on any theory of liability, whether in contract, strict
liability, or tort (including negligence), arising in any way out of the use of this software, even if
advised of the possibility of such damage.

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
----------------------------------------------------------------------------------------------------------- */

/*****************************  MPEG-4 AAC Encoder  **************************

   Author(s):   M. Werner
   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);


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

static INT FDKaacEnc_GetWindowIndex(INT blockSwWindowIndex);

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

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



/****************** Routines ****************************/
void FDKaacEnc_InitBlockSwitching(BLOCK_SWITCHING_CONTROL *blockSwitchingControl, INT isLowDelay)
{
  /* note: the pointer to timeSignal can be zeroed here, because it is initialized for every call
           to FDKaacEnc_BlockSwitching anew */
  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)
{
    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 ));

    /* 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)
{
    INT  i;
    UINT w;

    FIXP_SGL hiPassCoeff0 = hiPassCoeff[0];
    FIXP_SGL hiPassCoeff1 = hiPassCoeff[1];

    INT_PCM *timeSignal = blockSwitchingControl->timeSignal;

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

        FIXP_DBL temp_windowNrg  = FL2FXCONST_DBL(0.0f);
        FIXP_DBL temp_windowNrgF = FL2FXCONST_DBL(0.0f);
        FIXP_DBL temp_iirState0  = blockSwitchingControl->iirStates[0];
        FIXP_DBL temp_iirState1  = blockSwitchingControl->iirStates[1];

        /* windowNrg = sum(timesample^2) */
        for(i=0;i<windowLen;i++)
        {

            FIXP_DBL tempUnfiltered, tempFiltred, t1, t2;
            /* tempUnfiltered is scaled with 1 to prevent overflows during calculation of tempFiltred */
#if SAMPLE_BITS == DFRACT_BITS
            tempUnfiltered = (FIXP_DBL) *timeSignal++ >> 1;
#else
            tempUnfiltered = (FIXP_DBL) *timeSignal++ << (DFRACT_BITS-SAMPLE_BITS-1);
#endif
            t1 = fMultDiv2(hiPassCoeff1, tempUnfiltered-temp_iirState0);
            t2 = fMultDiv2(hiPassCoeff0, temp_iirState1);
            tempFiltred = (t1 - t2) << 1;

            temp_iirState0 = tempUnfiltered;
            temp_iirState1 = tempFiltred;

            /* subtract 2 from overallscaling (BLOCK_SWITCH_ENERGY_SHIFT)
             * because tempUnfiltered was already scaled with 1 (is 2 after squaring)
             * subtract 1 from overallscaling (BLOCK_SWITCH_ENERGY_SHIFT)
             * because of fMultDiv2 is doing a scaling by one */
            temp_windowNrg += fPow2Div2(tempUnfiltered) >> (BLOCK_SWITCH_ENERGY_SHIFT - 1 - 2);
            temp_windowNrgF += fPow2Div2(tempFiltred) >> (BLOCK_SWITCH_ENERGY_SHIFT - 1 - 2);
        }
        blockSwitchingControl->windowNrg[1][w]  = temp_windowNrg;
        blockSwitchingControl->windowNrgF[1][w] = temp_windowNrgF;
        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;
}