aac: Reset some state variables when turning SBR off

This makes sure the reset flag gets set when SBR gets turned back on
and sets control variables for unguided mode back to their defaults.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org

libavcodec/aacsbr.c

@@ -127,11 +127,22 @@ av_cold void ff_aac_sbr_init(void)
     ff_ps_init();
 }
 
+/** Places SBR in pure upsampling mode. */
+static void sbr_turnoff(SpectralBandReplication *sbr) {
+    sbr->start = 0;
+    // Init defults used in pure upsampling mode
+    sbr->kx[1] = 32; //Typo in spec, kx' inits to 32
+    sbr->m[1] = 0;
+    // Reset values for first SBR header
+    sbr->data[0].e_a[1] = sbr->data[1].e_a[1] = -1;
+    memset(&sbr->spectrum_params, -1, sizeof(SpectrumParameters));
+}
+
 av_cold void ff_aac_sbr_ctx_init(AACContext *ac, SpectralBandReplication *sbr)
 {
     float mdct_scale;
-    sbr->kx[0] = sbr->kx[1] = 32; //Typo in spec, kx' inits to 32
-    sbr->data[0].e_a[1] = sbr->data[1].e_a[1] = -1;
+    sbr->kx[0] = sbr->kx[1];
+    sbr_turnoff(sbr);
     sbr->data[0].synthesis_filterbank_samples_offset = SBR_SYNTHESIS_BUF_SIZE - (1280 - 128);
     sbr->data[1].synthesis_filterbank_samples_offset = SBR_SYNTHESIS_BUF_SIZE - (1280 - 128);
     /* SBR requires samples to be scaled to +/-32768.0 to work correctly.
@@ -994,18 +1005,18 @@ static unsigned int read_sbr_data(AACContext *ac, SpectralBandReplication *sbr,
 
     if (id_aac == TYPE_SCE || id_aac == TYPE_CCE) {
         if (read_sbr_single_channel_element(ac, sbr, gb)) {
-            sbr->start = 0;
+            sbr_turnoff(sbr);
             return get_bits_count(gb) - cnt;
         }
     } else if (id_aac == TYPE_CPE) {
         if (read_sbr_channel_pair_element(ac, sbr, gb)) {
-            sbr->start = 0;
+            sbr_turnoff(sbr);
             return get_bits_count(gb) - cnt;
         }
     } else {
         av_log(ac->avctx, AV_LOG_ERROR,
             "Invalid bitstream - cannot apply SBR to element type %d\n", id_aac);
-        sbr->start = 0;
+        sbr_turnoff(sbr);
         return get_bits_count(gb) - cnt;
     }
     if (get_bits1(gb)) { // bs_extended_data
@@ -1037,7 +1048,7 @@ static void sbr_reset(AACContext *ac, SpectralBandReplication *sbr)
     if (err < 0) {
         av_log(ac->avctx, AV_LOG_ERROR,
                "SBR reset failed. Switching SBR to pure upsampling mode.\n");
-        sbr->start = 0;
+        sbr_turnoff(sbr);
     }
 }
 
@@ -1072,6 +1083,7 @@ int ff_decode_sbr_extension(AACContext *ac, SpectralBandReplication *sbr,
     //Save some state from the previous frame.
     sbr->kx[0] = sbr->kx[1];
     sbr->m[0] = sbr->m[1];
+    sbr->kx_and_m_pushed = 1;
 
     num_sbr_bits++;
     if (get_bits1(gb)) // bs_header_flag
@@ -1633,6 +1645,13 @@ void ff_sbr_apply(AACContext *ac, SpectralBandReplication *sbr, int id_aac,
     int ch;
     int nch = (id_aac == TYPE_CPE) ? 2 : 1;
 
+    if (!sbr->kx_and_m_pushed) {
+        sbr->kx[0] = sbr->kx[1];
+        sbr->m[0] = sbr->m[1];
+    } else {
+        sbr->kx_and_m_pushed = 0;
+    }
+
     if (sbr->start) {
         sbr_dequant(sbr, id_aac);
     }
@@ -1642,6 +1661,7 @@ void ff_sbr_apply(AACContext *ac, SpectralBandReplication *sbr, int id_aac,
                          (float*)sbr->qmf_filter_scratch,
                          sbr->data[ch].W);
         sbr_lf_gen(ac, sbr, sbr->X_low, sbr->data[ch].W);
+        sbr->data[ch].Ypos ^= 1;
         if (sbr->start) {
             sbr_hf_inverse_filter(&sbr->dsp, sbr->alpha0, sbr->alpha1, sbr->X_low, sbr->k[0]);
             sbr_chirp(sbr, &sbr->data[ch]);
@@ -1653,7 +1673,6 @@ void ff_sbr_apply(AACContext *ac, SpectralBandReplication *sbr, int id_aac,
             sbr_mapping(ac, sbr, &sbr->data[ch], sbr->data[ch].e_a);
             sbr_env_estimate(sbr->e_curr, sbr->X_high, sbr, &sbr->data[ch]);
             sbr_gain_calc(ac, sbr, &sbr->data[ch], sbr->data[ch].e_a);
-            sbr->data[ch].Ypos ^= 1;
             sbr_hf_assemble(sbr->data[ch].Y[sbr->data[ch].Ypos],
                             sbr->X_high, sbr, &sbr->data[ch],
                             sbr->data[ch].e_a);

libavcodec/sbr.h

@@ -133,6 +133,7 @@ typedef struct {
     unsigned           kx[2];
     ///M' and M respectively, M is the number of QMF subbands that use SBR.
     unsigned           m[2];
+    unsigned           kx_and_m_pushed;
     ///The number of frequency bands in f_master
     unsigned           n_master;
     SBRData            data[2];