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Improving the transient detection

When a transient occurs in the overlap between two frames, we
now make sure that both these frames are coded as transients

--- a/libcelt/celt.c

+++ b/libcelt/celt.c

@@ -95,6 +95,7 @@

    celt_word16 gain_prod;

    celt_word32 frame_max;

    int start, end;

+   int next_transient;

    /* VBR-related parameters */

    celt_int32 vbr_reservoir;

@@ -175,6 +176,7 @@

    st->delayedIntra = 1;

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

    st->fold_decision = 1;

+   st->next_transient = 0;

    st->in_mem = celt_alloc(st->overlap*C*sizeof(celt_sig));

    st->out_mem = celt_alloc((MAX_PERIOD+st->overlap)*C*sizeof(celt_sig));

@@ -259,9 +261,9 @@

 static int transient_analysis(const celt_word32 * restrict in, int len, int C,

                               int *transient_time, int *transient_shift,

-                              celt_word32 *frame_max)

+                              int *next, celt_word32 *frame_max, int overlap)

 {

-   int i, n;

+   int i, n, ret;

    celt_word32 ratio;

    celt_word32 threshold;

    VARDECL(celt_word32, begin);

@@ -312,8 +314,10 @@

    *transient_time = n;

    *frame_max = begin[len];

+   ret = ratio > 20 || *next;

+   *next = ret && n>len-overlap;

    RESTORE_STACK;

-   return ratio > 20;

+   return ret;

 }

 /** Apply window and compute the MDCT for all sub-frames and 

@@ -630,7 +634,7 @@

    resynth = st->pitch_available>0 || optional_resynthesis!=NULL;

-   if (M > 1 && transient_analysis(in, N+st->overlap, C, &transient_time, &transient_shift, &st->frame_max))

+   if (M > 1 && transient_analysis(in, N+st->overlap, C, &transient_time, &transient_shift, &st->next_transient, &st->frame_max, st->overlap))

    {

 #ifndef FIXED_POINT

       float gain_1;

@@ -719,7 +723,7 @@

       st->delayedIntra = 0;

    NN = M*st->mode->eBands[st->mode->nbEBands];

-   if (shortBlocks && !transient_shift) 

+   if (shortBlocks && !transient_shift)

    {

       celt_word32 sum[8]={1,1,1,1,1,1,1,1};

       int m;