Reopen the OPUS decoder when a note moves to another sample (#7137)

The decoder cached on a note was keyed on nothing, so a note reused for a
different streamed sample carried on decoding the previous track. Audible as
the wrong custom music: the sequence and soundfont the audio editor reports
are correct, only the samples reaching the mixer are not.

Reproduced on the game-start cutscene chain with a streamed music pack in 4
of 6 runs; 0 of 6 after.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
Co-authored-by: serprex <159546+serprex@users.noreply.github.com>

soh/include/z64audio.h

@@ -468,7 +468,7 @@ typedef struct {
     /* 0x00F0 */ s16 dummyResampleState[0x10];
 } NoteSynthesisBuffers; // size = 0x110
 
-struct OggOpusFile;
+struct OpusDecState;
 
 typedef struct {
     /* 0x00 */ u8 restart;
@@ -488,7 +488,7 @@ typedef struct {
     /* 0x1A */ u8 unk_1A;
     /* 0x1C */ u16 unk_1C;
     /* 0x1E */ u16 unk_1E;
-    struct OggOpusFile* opusFile; // Only for streamed opus audio
+    struct OpusDecState* opusFile; // Only for streamed opus audio
 } NoteSynthesisState; // size = 0x20
 
 typedef struct {

soh/soh/mixer.c

@@ -2,6 +2,7 @@
 //! when unoptimized and clang does not allow optimizing a single function.
 
 #include <stdint.h>
+#include <stdlib.h>
 #include <string.h>
 
 #include "mixer.h"
@@ -108,28 +109,52 @@ void aLoadBufferImpl(const void* source_addr, uint16_t dest_addr, uint16_t nbyte
 
 #include <opusfile.h>
 
-void aOPUSdecImpl(void* source_addr, uint16_t dest_addr, uint16_t nbytes, struct OggOpusFile** decState, int32_t pos,
+// The decoder is cached on the note, so remember which buffer it was opened for.
+struct OpusDecState {
+    OggOpusFile* file;
+    const void* source;
+};
+
+void aOPUSdecImpl(void* source_addr, uint16_t dest_addr, uint16_t nbytes, struct OpusDecState** decState, int32_t pos,
                   uint32_t size) {
     int readSamples = 0;
-    if (*decState == NULL) {
-        *decState = op_open_memory(source_addr, size, NULL);
+    struct OpusDecState* dec = *decState;
+
+    // Note reused for another streamed sample may have previous decoder opened,
+    // which would keep playing the previous track under new note.
+    if (dec != NULL && dec->source != source_addr) {
+        aOPUSFree(dec);
+        dec = NULL;
+        *decState = NULL;
     }
-    op_pcm_seek(*decState, pos);
-    int ret = op_read(*decState, BUF_S16(dest_addr), nbytes / 2, NULL);
+    if (dec == NULL) {
+        OggOpusFile* file = op_open_memory(source_addr, size, NULL);
+        if (file == NULL) {
+            return;
+        }
+        dec = malloc(sizeof(struct OpusDecState));
+        dec->file = file;
+        dec->source = source_addr;
+        *decState = dec;
+    }
+
+    op_pcm_seek(dec->file, pos);
+    int ret = op_read(dec->file, BUF_S16(dest_addr), nbytes / 2, NULL);
     if (ret < 0) {
         return;
     }
     readSamples += ret;
     while (readSamples < nbytes / 2) {
-        ret = op_read(*decState, BUF_S16(dest_addr + readSamples * 2), (nbytes - readSamples * 2) / 2, NULL);
+        ret = op_read(dec->file, BUF_S16(dest_addr + readSamples * 2), (nbytes - readSamples * 2) / 2, NULL);
         if (ret == 0)
             break;
         readSamples += ret;
     }
 }
 
-void aOPUSFree(struct OggOpusFile* opusFile) {
-    op_free(opusFile);
+void aOPUSFree(struct OpusDecState* dec) {
+    op_free(dec->file);
+    free(dec);
 }
 
 void aSaveBufferImpl(uint16_t source_addr, int16_t* dest_addr, uint16_t nbytes) {

soh/soh/mixer.h

@@ -57,10 +57,11 @@ void aHiLoGainImpl(uint8_t g, uint16_t count, uint16_t addr);
 void aUnkCmd3Impl(uint16_t a, uint16_t b, uint16_t c);
 void aUnkCmd19Impl(uint8_t f, uint16_t count, uint16_t out_addr, uint16_t in_addr);
 
-struct OggOpusFile;
+struct OpusDecState;
 
-void aOPUSdecImpl(void* source_addr, uint16_t dest_addr, uint16_t nbytes, struct OggOpusFile** decState, int32_t pos,
+void aOPUSdecImpl(void* source_addr, uint16_t dest_addr, uint16_t nbytes, struct OpusDecState** decState, int32_t pos,
                   uint32_t size);
+void aOPUSFree(struct OpusDecState* dec);
 
 #define aSegment(pkt, s, b) \
     do {                    \

soh/src/code/audio_playback.c

@@ -150,7 +150,7 @@ void Audio_NoteInit(Note* note) {
     note->noteSubEu = gDefaultNoteSub;
 }
 
-extern void aOPUSFree(struct OggOpusFile* opusFile);
+extern void aOPUSFree(struct OpusDecState* dec);
 void Audio_NoteDisable(Note* note) {
     if (note->noteSubEu.bitField0.needsInit == true) {
         note->noteSubEu.bitField0.needsInit = false;