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Better fading for PLC: no fading for the first loss, muting after 6

--- a/libcelt/celt.c

+++ b/libcelt/celt.c

@@ -1112,6 +1112,7 @@

    celt_word16_t *oldBandE;

    int last_pitch_index;

+   int loss_count;

 };

 int check_decoder(const CELTDecoder *st) 

@@ -1158,7 +1159,7 @@

    st->preemph_memD = (celt_sig_t*)celt_alloc(C*sizeof(celt_sig_t));

-   st->last_pitch_index = 0;

+   st->loss_count = 0;

    if ((st->decode_mem!=NULL) && (st->out_mem!=NULL) && (st->oldBandE!=NULL) &&

        (st->preemph_memD!=NULL))

@@ -1215,6 +1216,7 @@

 {

    int c, N;

    int pitch_index;

+   celt_word16_t fade = Q15ONE;

    int i, len;

    VARDECL(celt_sig_t, freq);

    const int C = CHANNELS(st->mode);

@@ -1224,25 +1226,27 @@

    ALLOC(freq,C*N, celt_sig_t); /**< Interleaved signal MDCTs */

    len = N+st->mode->overlap;

-#if 0

-   pitch_index = st->last_pitch_index;

-   /* Use the pitch MDCT as the "guessed" signal */

-   compute_mdcts(st->mode, st->mode->window, st->out_mem+pitch_index*C, freq);

+   if (st->loss_count == 0)

+   {

+      find_spectral_pitch(st->mode, st->mode->fft, &st->mode->psy, st->out_mem+MAX_PERIOD-len, st->out_mem, st->mode->window, NULL, len, MAX_PERIOD-len-100, &pitch_index);

+      pitch_index = MAX_PERIOD-len-pitch_index;

+      st->last_pitch_index = pitch_index;

+   } else {

+      pitch_index = st->last_pitch_index;

+      if (st->loss_count < 5)

+         fade = QCONST16(.8f,15);

+      else

+         fade = 0;

+   }

-#else

-   find_spectral_pitch(st->mode, st->mode->fft, &st->mode->psy, st->out_mem+MAX_PERIOD-len, st->out_mem, st->mode->window, NULL, len, MAX_PERIOD-len-100, &pitch_index);

-   pitch_index = MAX_PERIOD-len-pitch_index;

    offset = MAX_PERIOD-pitch_index;

    while (offset+len >= MAX_PERIOD)

       offset -= pitch_index;

    compute_mdcts(st->mode, 0, st->out_mem+offset*C, freq);

    for (i=0;i<C*N;i++)

-      freq[i] = ADD32(EPSILON, MULT16_32_Q15(QCONST16(.9f,15),freq[i]));

-#endif

-   

-   

-   

+      freq[i] = ADD32(VERY_SMALL, MULT16_32_Q15(fade,freq[i]));

+

    CELT_MOVE(st->out_mem, st->out_mem+C*N, C*(MAX_PERIOD+st->mode->overlap-N));

    /* Compute inverse MDCTs */

    compute_inv_mdcts(st->mode, 0, freq, -1, 0, st->out_mem);

@@ -1258,6 +1262,9 @@

          pcm[C*j+c] = SCALEOUT(SIG2WORD16(tmp));

       }

    }

+   

+   st->loss_count++;

+

    RESTORE_STACK;

 }

 #endif

@@ -1317,6 +1324,8 @@

       celt_decode_lost(st, pcm);

       RESTORE_STACK;

       return 0;

+   } else {

+      st->loss_count = 0;

    }

    if (len<0) {

      RESTORE_STACK;

@@ -1348,7 +1357,6 @@

    if (has_pitch)

    {

       pitch_index = ec_dec_uint(&dec, MAX_PERIOD-(2*N-2*N4));

-      st->last_pitch_index = pitch_index;

    } else {

       pitch_index = 0;

       for (i=0;i<st->mode->nbPBands;i++)

@@ -1525,7 +1533,7 @@

          CELT_MEMSET(st->preemph_memD, 0, C);

-         st->last_pitch_index = 0;

+         st->loss_count = 0;

       }

       break;

       default: