aacenc: add support for encoding files using Long Term Prediction

Long Term Prediction allows for prediction of spectral coefficients
via the previously decoded time-dependent samples. This feature
works well with harmonic content 2 or more frames long, like speech,
human or non-human, piano music or any constant tones at very low
bitrates.

It should be noted that the current coder is highly efficient and
the rate control system is unable to encode files at extremely
low bitrates (less than 14kbps seems to be impossible) so this
extension isn't capable of optimum operation. Dramatic difference
is observable with some types of audio and speech but for the most
part the audiable differences are subtle. The spectrum looks better
however so the encoder is able to harvest the additional bits that
this feature provies, should the user choose to enable it. So
it's best to enable this feature only if encoding at the absolutely
lowest bitrate that the encoder is capable of.

7 files changed, 341 insertions, 0 deletions

diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index 1e1e479473..af93f8acb9 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -135,6 +135,7 @@ OBJS-$(CONFIG_AAC_ENCODER)             += aacenc.o aaccoder.o aacenctab.o    \
                                           aacpsy.o aactab.o      \
                                           aacenc_is.o \
                                           aacenc_tns.o \
+                                          aacenc_ltp.o \
                                           aacenc_pred.o \
                                           psymodel.o mpeg4audio.o kbdwin.o
 OBJS-$(CONFIG_AASC_DECODER)            += aasc.o msrledec.o
diff --git a/libavcodec/aac.h b/libavcodec/aac.h
index 37f98adb31..3333bfe5b2 100644
--- a/libavcodec/aac.h
+++ b/libavcodec/aac.h
@@ -161,6 +161,7 @@ typedef struct PredictorState {
 typedef struct LongTermPrediction {
     int8_t present;
     int16_t lag;
+    int coef_idx;
     INTFLOAT coef;
     int8_t used[MAX_LTP_LONG_SFB];
 } LongTermPrediction;
@@ -260,6 +261,7 @@ typedef struct SingleChannelElement {
     DECLARE_ALIGNED(32, INTFLOAT, saved)[1536];     ///< overlap
     DECLARE_ALIGNED(32, INTFLOAT, ret_buf)[2048];   ///< PCM output buffer
     DECLARE_ALIGNED(16, INTFLOAT, ltp_state)[3072]; ///< time signal for LTP
+    DECLARE_ALIGNED(32, AAC_FLOAT, lcoeffs)[1024];  ///< MDCT of LTP coefficients (used by encoder)
     DECLARE_ALIGNED(32, AAC_FLOAT, prcoeffs)[1024]; ///< Main prediction coefs (used by encoder)
     PredictorState predictor_state[MAX_PREDICTORS];
     INTFLOAT *ret;                                  ///< PCM output
diff --git a/libavcodec/aaccoder.c b/libavcodec/aaccoder.c
index c25189dbda..fd9785e26a 100644
--- a/libavcodec/aaccoder.c
+++ b/libavcodec/aaccoder.c
@@ -48,6 +48,7 @@
 
 #include "aacenc_is.h"
 #include "aacenc_tns.h"
+#include "aacenc_ltp.h"
 #include "aacenc_pred.h"
 
 #include "libavcodec/aaccoder_twoloop.h"
@@ -911,14 +912,19 @@ AACCoefficientsEncoder ff_aac_coders[AAC_CODER_NB] = {
         encode_window_bands_info,
         quantize_and_encode_band,
         ff_aac_encode_tns_info,
+        ff_aac_encode_ltp_info,
         ff_aac_encode_main_pred,
         ff_aac_adjust_common_pred,
+        ff_aac_adjust_common_ltp,
         ff_aac_apply_main_pred,
         ff_aac_apply_tns,
+        ff_aac_update_ltp,
+        ff_aac_ltp_insert_new_frame,
         set_special_band_scalefactors,
         search_for_pns,
         mark_pns,
         ff_aac_search_for_tns,
+        ff_aac_search_for_ltp,
         search_for_ms,
         ff_aac_search_for_is,
         ff_aac_search_for_pred,
@@ -928,14 +934,19 @@ AACCoefficientsEncoder ff_aac_coders[AAC_CODER_NB] = {
         encode_window_bands_info,
         quantize_and_encode_band,
         ff_aac_encode_tns_info,
+        ff_aac_encode_ltp_info,
         ff_aac_encode_main_pred,
         ff_aac_adjust_common_pred,
+        ff_aac_adjust_common_ltp,
         ff_aac_apply_main_pred,
         ff_aac_apply_tns,
+        ff_aac_update_ltp,
+        ff_aac_ltp_insert_new_frame,
         set_special_band_scalefactors,
         search_for_pns,
         mark_pns,
         ff_aac_search_for_tns,
+        ff_aac_search_for_ltp,
         search_for_ms,
         ff_aac_search_for_is,
         ff_aac_search_for_pred,
@@ -945,14 +956,19 @@ AACCoefficientsEncoder ff_aac_coders[AAC_CODER_NB] = {
         codebook_trellis_rate,
         quantize_and_encode_band,
         ff_aac_encode_tns_info,
+        ff_aac_encode_ltp_info,
         ff_aac_encode_main_pred,
         ff_aac_adjust_common_pred,
+        ff_aac_adjust_common_ltp,
         ff_aac_apply_main_pred,
         ff_aac_apply_tns,
+        ff_aac_update_ltp,
+        ff_aac_ltp_insert_new_frame,
         set_special_band_scalefactors,
         search_for_pns,
         mark_pns,
         ff_aac_search_for_tns,
+        ff_aac_search_for_ltp,
         search_for_ms,
         ff_aac_search_for_is,
         ff_aac_search_for_pred,
@@ -962,14 +978,19 @@ AACCoefficientsEncoder ff_aac_coders[AAC_CODER_NB] = {
         encode_window_bands_info,
         quantize_and_encode_band,
         ff_aac_encode_tns_info,
+        ff_aac_encode_ltp_info,
         ff_aac_encode_main_pred,
         ff_aac_adjust_common_pred,
+        ff_aac_adjust_common_ltp,
         ff_aac_apply_main_pred,
         ff_aac_apply_tns,
+        ff_aac_update_ltp,
+        ff_aac_ltp_insert_new_frame,
         set_special_band_scalefactors,
         search_for_pns,
         mark_pns,
         ff_aac_search_for_tns,
+        ff_aac_search_for_ltp,
         search_for_ms,
         ff_aac_search_for_is,
         ff_aac_search_for_pred,
diff --git a/libavcodec/aacenc.c b/libavcodec/aacenc.c
index 8d5f4387f3..9454a9491b 100644
--- a/libavcodec/aacenc.c
+++ b/libavcodec/aacenc.c
@@ -60,6 +60,7 @@ static const struct AACProfileOptions aacenc_profiles[] = {
             .mid_side = 0,
             .pns = 1,
             .tns = 0,
+            .ltp = OPT_BANNED,
             .pred = OPT_REQUIRED,
             .intensity_stereo = 1,
         },
@@ -69,6 +70,7 @@ static const struct AACProfileOptions aacenc_profiles[] = {
             .mid_side = 0,
             .pns = 1,
             .tns = 0,
+            .ltp = OPT_NEEDS_LTP,
             .pred = OPT_NEEDS_MAIN,
             .intensity_stereo = 1,
         },
@@ -78,6 +80,17 @@ static const struct AACProfileOptions aacenc_profiles[] = {
             .mid_side = 0,
             .pns = OPT_BANNED,
             .tns = 0,
+            .ltp = OPT_BANNED,
+            .pred = OPT_BANNED,
+            .intensity_stereo = 1,
+        },
+    },
+    {FF_PROFILE_AAC_LTP,
+        {  /* Long term prediction profile */
+            .mid_side = 0,
+            .pns = 1,
+            .tns = 0,
+            .ltp = OPT_REQUIRED,
             .pred = OPT_BANNED,
             .intensity_stereo = 1,
         },
@@ -475,6 +488,8 @@ static int encode_individual_channel(AVCodecContext *avctx, AACEncContext *s,
         put_ics_info(s, &sce->ics);
         if (s->coder->encode_main_pred)
             s->coder->encode_main_pred(s, sce);
+        if (s->coder->encode_ltp_info)
+            s->coder->encode_ltp_info(s, sce, 0);
     }
     encode_band_info(s, sce);
     encode_scale_factors(avctx, s, sce);
@@ -625,6 +640,13 @@ static int aac_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
             }
 
             apply_window_and_mdct(s, sce, overlap);
+
+            if (s->options.ltp && s->coder->update_ltp) {
+                s->coder->update_ltp(s, sce);
+                apply_window[sce->ics.window_sequence[0]](s->fdsp, sce, &sce->ltp_state[0]);
+                s->mdct1024.mdct_calc(&s->mdct1024, sce->lcoeffs, sce->ret_buf);
+            }
+
             if (isnan(cpe->ch->coeffs[0])) {
                 av_log(avctx, AV_LOG_ERROR, "Input contains NaN\n");
                 return AVERROR(EINVAL);
@@ -659,6 +681,8 @@ static int aac_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
                 sce = &cpe->ch[ch];
                 coeffs[ch] = sce->coeffs;
                 sce->ics.predictor_present = 0;
+                sce->ics.ltp.present = 0;
+                memset(sce->ics.ltp.used, 0, sizeof(sce->ics.ltp.used));
                 memset(sce->ics.prediction_used, 0, sizeof(sce->ics.prediction_used));
                 memset(&sce->tns, 0, sizeof(TemporalNoiseShaping));
                 for (w = 0; w < 128; w++)
@@ -738,12 +762,26 @@ static int aac_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
                 apply_mid_side_stereo(cpe);
             }
             adjust_frame_information(cpe, chans);
+            if (s->options.ltp) { /* LTP */
+                for (ch = 0; ch < chans; ch++) {
+                    sce = &cpe->ch[ch];
+                    s->cur_channel = start_ch + ch;
+                    if (s->coder->search_for_ltp)
+                        s->coder->search_for_ltp(s, sce, cpe->common_window);
+                    if (sce->ics.ltp.present) pred_mode = 1;
+                }
+                s->cur_channel = start_ch;
+                if (s->coder->adjust_common_ltp)
+                    s->coder->adjust_common_ltp(s, cpe);
+            }
             if (chans == 2) {
                 put_bits(&s->pb, 1, cpe->common_window);
                 if (cpe->common_window) {
                     put_ics_info(s, &cpe->ch[0].ics);
                     if (s->coder->encode_main_pred)
                         s->coder->encode_main_pred(s, &cpe->ch[0]);
+                    if (s->coder->encode_ltp_info)
+                        s->coder->encode_ltp_info(s, &cpe->ch[0], 1);
                     encode_ms_info(&s->pb, cpe);
                     if (cpe->ms_mode) ms_mode = 1;
                 }
@@ -816,6 +854,9 @@ static int aac_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
         }
     } while (1);
 
+    if (s->options.ltp && s->coder->ltp_insert_new_frame)
+        s->coder->ltp_insert_new_frame(s);
+
     put_bits(&s->pb, 3, TYPE_END);
     flush_put_bits(&s->pb);
     avctx->frame_bits = put_bits_count(&s->pb);
@@ -935,6 +976,7 @@ static av_cold int aac_encode_init(AVCodecContext *avctx)
     AAC_OPT_SET(&s->options, p_opt, 1, coder);
     AAC_OPT_SET(&s->options, p_opt, 0, pns);
     AAC_OPT_SET(&s->options, p_opt, 1, tns);
+    AAC_OPT_SET(&s->options, p_opt, 0, ltp);
     AAC_OPT_SET(&s->options, p_opt, 0, pred);
     AAC_OPT_SET(&s->options, p_opt, 1, mid_side);
     AAC_OPT_SET(&s->options, p_opt, 0, intensity_stereo);
@@ -993,6 +1035,7 @@ static const AVOption aacenc_options[] = {
     {"aac_is", "Intensity stereo coding", offsetof(AACEncContext, options.intensity_stereo), AV_OPT_TYPE_BOOL, {.i64 = OPT_AUTO}, -1, 1, AACENC_FLAGS},
     {"aac_pns", "Perceptual noise substitution", offsetof(AACEncContext, options.pns), AV_OPT_TYPE_BOOL, {.i64 = OPT_AUTO}, -1, 1, AACENC_FLAGS},
     {"aac_tns", "Temporal noise shaping", offsetof(AACEncContext, options.tns), AV_OPT_TYPE_BOOL, {.i64 = 0}, -1, 1, AACENC_FLAGS},
+    {"aac_ltp", "Long term prediction", offsetof(AACEncContext, options.ltp), AV_OPT_TYPE_BOOL, {.i64 = OPT_AUTO}, -1, 1, AACENC_FLAGS},
     {"aac_pred", "AAC-Main prediction", offsetof(AACEncContext, options.pred), AV_OPT_TYPE_BOOL, {.i64 = OPT_AUTO}, -1, 1, AACENC_FLAGS},
     {NULL}
 };
diff --git a/libavcodec/aacenc.h b/libavcodec/aacenc.h
index 0f4fc05e3d..d8bed82abe 100644
--- a/libavcodec/aacenc.h
+++ b/libavcodec/aacenc.h
@@ -45,6 +45,7 @@ typedef struct AACEncOptions {
     int coder;
     int pns;
     int tns;
+    int ltp;
     int pred;
     int mid_side;
     int intensity_stereo;
@@ -60,14 +61,19 @@ typedef struct AACCoefficientsEncoder {
     void (*quantize_and_encode_band)(struct AACEncContext *s, PutBitContext *pb, const float *in, float *out, int size,
                                      int scale_idx, int cb, const float lambda, int rtz);
     void (*encode_tns_info)(struct AACEncContext *s, SingleChannelElement *sce);
+    void (*encode_ltp_info)(struct AACEncContext *s, SingleChannelElement *sce, int common_window);
     void (*encode_main_pred)(struct AACEncContext *s, SingleChannelElement *sce);
     void (*adjust_common_pred)(struct AACEncContext *s, ChannelElement *cpe);
+    void (*adjust_common_ltp)(struct AACEncContext *s, ChannelElement *cpe);
     void (*apply_main_pred)(struct AACEncContext *s, SingleChannelElement *sce);
     void (*apply_tns_filt)(struct AACEncContext *s, SingleChannelElement *sce);
+    void (*update_ltp)(struct AACEncContext *s, SingleChannelElement *sce);
+    void (*ltp_insert_new_frame)(struct AACEncContext *s);
     void (*set_special_band_scalefactors)(struct AACEncContext *s, SingleChannelElement *sce);
     void (*search_for_pns)(struct AACEncContext *s, AVCodecContext *avctx, SingleChannelElement *sce);
     void (*mark_pns)(struct AACEncContext *s, AVCodecContext *avctx, SingleChannelElement *sce);
     void (*search_for_tns)(struct AACEncContext *s, SingleChannelElement *sce);
+    void (*search_for_ltp)(struct AACEncContext *s, SingleChannelElement *sce, int common_window);
     void (*search_for_ms)(struct AACEncContext *s, ChannelElement *cpe);
     void (*search_for_is)(struct AACEncContext *s, AVCodecContext *avctx, ChannelElement *cpe);
     void (*search_for_pred)(struct AACEncContext *s, SingleChannelElement *sce);
diff --git a/libavcodec/aacenc_ltp.c b/libavcodec/aacenc_ltp.c
new file mode 100644
index 0000000000..066e1952e7
--- /dev/null
+++ b/libavcodec/aacenc_ltp.c
@@ -0,0 +1,227 @@
+/*
+ * AAC encoder TNS
+ * Copyright (C) 2015 Rostislav Pehlivanov
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * AAC encoder long term prediction
+ * @author Rostislav Pehlivanov ( atomnuker gmail com )
+ */
+
+#include "aacenc_ltp.h"
+#include "aacenc_quantization.h"
+#include "aacenc_utils.h"
+
+/**
+ * Encode LTP data.
+ */
+void ff_aac_encode_ltp_info(AACEncContext *s, SingleChannelElement *sce,
+                            int common_window)
+{
+    int i;
+    IndividualChannelStream *ics = &sce->ics;
+    if (s->profile != FF_PROFILE_AAC_LTP || !ics->predictor_present)
+        return;
+    if (common_window)
+        put_bits(&s->pb, 1, 0);
+    put_bits(&s->pb, 1, ics->ltp.present);
+    if (!ics->ltp.present)
+        return;
+    put_bits(&s->pb, 11, ics->ltp.lag);
+    put_bits(&s->pb, 3,  ics->ltp.coef_idx);
+    for (i = 0; i < FFMIN(ics->max_sfb, MAX_LTP_LONG_SFB); i++)
+        put_bits(&s->pb, 1, ics->ltp.used[i]);
+}
+
+void ff_aac_ltp_insert_new_frame(AACEncContext *s)
+{
+    int i, ch, tag, chans, cur_channel, start_ch = 0;
+    ChannelElement *cpe;
+    SingleChannelElement *sce;
+    for (i = 0; i < s->chan_map[0]; i++) {
+        cpe = &s->cpe[i];
+        tag      = s->chan_map[i+1];
+        chans    = tag == TYPE_CPE ? 2 : 1;
+        for (ch = 0; ch < chans; ch++) {
+            sce = &cpe->ch[ch];
+            cur_channel = start_ch + ch;
+            /* New sample + overlap */
+            memcpy(&sce->ltp_state[0],    &sce->ltp_state[1024], 1024*sizeof(sce->ltp_state[0]));
+            memcpy(&sce->ltp_state[1024], &s->planar_samples[cur_channel][2048], 1024*sizeof(sce->ltp_state[0]));
+            memcpy(&sce->ltp_state[2048], &sce->ret_buf[0], 1024*sizeof(sce->ltp_state[0]));
+        }
+        start_ch += chans;
+    }
+}
+
+/**
+ * Process LTP parameters
+ * @see Patent WO2006070265A1
+ */
+void ff_aac_update_ltp(AACEncContext *s, SingleChannelElement *sce)
+{
+    int i, j, lag;
+    float corr, s0, s1, max_corr = 0.0f;
+    float *samples = &s->planar_samples[s->cur_channel][1024];
+    float *pred_signal = &sce->ltp_state[0];
+    int samples_num = 2048;
+
+    if (s->profile != FF_PROFILE_AAC_LTP)
+        return;
+
+    /* Calculate lag */
+    for (i = 0; i < samples_num; i++) {
+        s0 = s1 = 0.0f;
+        for (j = 0; j < samples_num; j++) {
+            if (j + 1024 < i)
+                continue;
+            s0 += samples[j]*pred_signal[j-i+1024];
+            s1 += pred_signal[j-i+1024]*pred_signal[j-i+1024];
+        }
+        corr = s1 > 0.0f ? s0/sqrt(s1) : 0.0f;
+        if (corr > max_corr) {
+            max_corr = corr;
+            lag = i;
+        }
+    }
+    lag = av_clip(lag, 0, 2048); /* 11 bits => 2^11 = 2048 */
+
+    if (!lag) {
+        sce->ics.ltp.lag = lag;
+        return;
+    }
+
+    s0 = s1 = 0.0f;
+    for (i = 0; i < lag; i++) {
+        s0 += samples[i];
+        s1 += pred_signal[i-lag+1024];
+    }
+
+    sce->ics.ltp.coef_idx = quant_array_idx(s0/s1, ltp_coef, 8);
+    sce->ics.ltp.coef     = ltp_coef[sce->ics.ltp.coef_idx];
+
+    /* Predict the new samples */
+    if (lag < 1024)
+        samples_num = lag + 1024;
+    for (i = 0; i < samples_num; i++)
+        pred_signal[i+1024] = sce->ics.ltp.coef*pred_signal[i-lag+1024];
+    memset(&pred_signal[samples_num], 0, (2048 - samples_num)*sizeof(float));
+
+    sce->ics.ltp.lag = lag;
+}
+
+void ff_aac_adjust_common_ltp(AACEncContext *s, ChannelElement *cpe)
+{
+    int sfb, count = 0;
+    SingleChannelElement *sce0 = &cpe->ch[0];
+    SingleChannelElement *sce1 = &cpe->ch[1];
+
+    if (!cpe->common_window ||
+        sce0->ics.window_sequence[0] == EIGHT_SHORT_SEQUENCE ||
+        sce1->ics.window_sequence[0] == EIGHT_SHORT_SEQUENCE)
+        return;
+
+    for (sfb = 0; sfb < FFMIN(sce0->ics.max_sfb, MAX_LTP_LONG_SFB); sfb++) {
+        int sum = sce0->ics.ltp.used[sfb] + sce1->ics.ltp.used[sfb];
+        if (sum != 2) {
+            sce0->ics.ltp.used[sfb] = 0;
+        } else if (sum == 2) {
+            count++;
+        }
+    }
+
+    sce0->ics.ltp.present = !!count;
+    sce0->ics.predictor_present = !!count;
+}
+
+/**
+ * Mark LTP sfb's
+ */
+void ff_aac_search_for_ltp(AACEncContext *s, SingleChannelElement *sce,
+                           int common_window)
+{
+    int w, g, w2, i, start = 0, count = 0;
+    int saved_bits = -(15 + FFMIN(sce->ics.max_sfb, MAX_LTP_LONG_SFB));
+    float *C34 = &s->scoefs[128*0], *PCD = &s->scoefs[128*1];
+    float *PCD34 = &s->scoefs[128*2];
+    const int max_ltp = FFMIN(sce->ics.max_sfb, MAX_LTP_LONG_SFB);
+
+    if (sce->ics.window_sequence[0] == EIGHT_SHORT_SEQUENCE ||
+        !sce->ics.ltp.lag)
+        return;
+
+    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
+        start = 0;
+        for (g = 0;  g < sce->ics.num_swb; g++) {
+            int bits1 = 0, bits2 = 0;
+            float dist1 = 0.0f, dist2 = 0.0f;
+            if (w*16+g > max_ltp) {
+                start += sce->ics.swb_sizes[g];
+                continue;
+            }
+            for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
+                int bits_tmp1, bits_tmp2;
+                FFPsyBand *band = &s->psy.ch[s->cur_channel].psy_bands[(w+w2)*16+g];
+                for (i = 0; i < sce->ics.swb_sizes[g]; i++)
+                    PCD[i] = sce->coeffs[start+(w+w2)*128+i] - sce->lcoeffs[start+(w+w2)*128+i];
+                abs_pow34_v(C34,  &sce->coeffs[start+(w+w2)*128],  sce->ics.swb_sizes[g]);
+                abs_pow34_v(PCD34, PCD, sce->ics.swb_sizes[g]);
+                dist1 += quantize_band_cost(s, &sce->coeffs[start+(w+w2)*128], C34, sce->ics.swb_sizes[g],
+                                            sce->sf_idx[(w+w2)*16+g], sce->band_type[(w+w2)*16+g],
+                                            s->lambda/band->threshold, INFINITY, &bits_tmp1, NULL, 0);
+                dist2 += quantize_band_cost(s, PCD, PCD34, sce->ics.swb_sizes[g],
+                                            sce->sf_idx[(w+w2)*16+g],
+                                            sce->band_type[(w+w2)*16+g],
+                                            s->lambda/band->threshold, INFINITY, &bits_tmp2, NULL, 0);
+                bits1 += bits_tmp1;
+                bits2 += bits_tmp2;
+            }
+            if (dist2 < dist1 && bits2 < bits1) {
+                for (w2 = 0; w2 < sce->ics.group_len[w]; w2++)
+                    for (i = 0; i < sce->ics.swb_sizes[g]; i++)
+                        sce->coeffs[start+(w+w2)*128+i] -= sce->lcoeffs[start+(w+w2)*128+i];
+                sce->ics.ltp.used[w*16+g] = 1;
+                saved_bits += bits1 - bits2;
+                count++;
+            }
+            start += sce->ics.swb_sizes[g];
+        }
+    }
+
+    sce->ics.ltp.present = !!count && (saved_bits >= 0);
+    sce->ics.predictor_present = !!sce->ics.ltp.present;
+
+    /* Reset any marked sfbs */
+    if (!sce->ics.ltp.present && !!count) {
+        for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
+            start = 0;
+            for (g = 0;  g < sce->ics.num_swb; g++) {
+                if (sce->ics.ltp.used[w*16+g]) {
+                    for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
+                        for (i = 0; i < sce->ics.swb_sizes[g]; i++) {
+                            sce->coeffs[start+(w+w2)*128+i] += sce->lcoeffs[start+(w+w2)*128+i];
+                        }
+                    }
+                }
+                start += sce->ics.swb_sizes[g];
+            }
+        }
+    }
+}
diff --git a/libavcodec/aacenc_ltp.h b/libavcodec/aacenc_ltp.h
new file mode 100644
index 0000000000..7276878427
--- /dev/null
+++ b/libavcodec/aacenc_ltp.h
@@ -0,0 +1,41 @@
+/*
+ * AAC encoder long term prediction extension
+ * Copyright (C) 2015 Rostislav Pehlivanov
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * AAC encoder long term prediction extension
+ * @author Rostislav Pehlivanov ( atomnuker gmail com )
+ */
+
+#ifndef AVCODEC_AACENC_LTP_H
+#define AVCODEC_AACENC_LTP_H
+
+#include "aacenc.h"
+
+void ff_aac_encode_ltp_info(AACEncContext *s, SingleChannelElement *sce,
+                            int common_window);
+void ff_aac_update_ltp(AACEncContext *s, SingleChannelElement *sce);
+void ff_aac_adjust_common_ltp(AACEncContext *s, ChannelElement *cpe);
+void ff_aac_ltp_insert_new_frame(AACEncContext *s);
+void ff_aac_search_for_ltp(AACEncContext *s, SingleChannelElement *sce,
+                           int common_window);
+
+#endif /* AVCODEC_AACENC_LTP_H */