Fixes a SILK bandwidth switching regression

The bug was triggered because f982b84d started using prefill for
SILK bandwidth changes, which reinitialized the encoder state and
prevented the variable lowpass from working properly. To fix the problem,
we preserve the sampling rate and variable low-pass when prefilling.

1 files changed, 11 insertions, 5 deletions

diff --git a/silk/control_audio_bandwidth.c b/silk/control_audio_bandwidth.c
index 4f9bc5cb..f6d22d83 100644
--- a/silk/control_audio_bandwidth.c
+++ b/silk/control_audio_bandwidth.c
@@ -39,9 +39,15 @@ opus_int silk_control_audio_bandwidth(
 )
 {
     opus_int   fs_kHz;
+    opus_int   orig_kHz;
     opus_int32 fs_Hz;
 
-    fs_kHz = psEncC->fs_kHz;
+    orig_kHz = psEncC->fs_kHz;
+    /* Handle a bandwidth-switching reset where we need to be aware what the last sampling rate was. */
+    if( orig_kHz == 0 ) {
+        orig_kHz = psEncC->sLP.saved_fs_kHz;
+    }
+    fs_kHz = orig_kHz;
     fs_Hz = silk_SMULBB( fs_kHz, 1000 );
     if( fs_Hz == 0 ) {
         /* Encoder has just been initialized */
@@ -61,7 +67,7 @@ opus_int silk_control_audio_bandwidth(
         }
         if( psEncC->allow_bandwidth_switch || encControl->opusCanSwitch ) {
             /* Check if we should switch down */
-            if( silk_SMULBB( psEncC->fs_kHz, 1000 ) > psEncC->desiredInternal_fs_Hz )
+            if( silk_SMULBB( orig_kHz, 1000 ) > psEncC->desiredInternal_fs_Hz )
             {
                 /* Switch down */
                 if( psEncC->sLP.mode == 0 ) {
@@ -76,7 +82,7 @@ opus_int silk_control_audio_bandwidth(
                     psEncC->sLP.mode = 0;
 
                     /* Switch to a lower sample frequency */
-                    fs_kHz = psEncC->fs_kHz == 16 ? 12 : 8;
+                    fs_kHz = orig_kHz == 16 ? 12 : 8;
                 } else {
                    if( psEncC->sLP.transition_frame_no <= 0 ) {
                        encControl->switchReady = 1;
@@ -90,12 +96,12 @@ opus_int silk_control_audio_bandwidth(
             }
             else
             /* Check if we should switch up */
-            if( silk_SMULBB( psEncC->fs_kHz, 1000 ) < psEncC->desiredInternal_fs_Hz )
+            if( silk_SMULBB( orig_kHz, 1000 ) < psEncC->desiredInternal_fs_Hz )
             {
                 /* Switch up */
                 if( encControl->opusCanSwitch ) {
                     /* Switch to a higher sample frequency */
-                    fs_kHz = psEncC->fs_kHz == 8 ? 12 : 16;
+                    fs_kHz = orig_kHz == 8 ? 12 : 16;
 
                     /* New transition */
                     psEncC->sLP.transition_frame_no = 0;