1 files changed, 128 insertions, 0 deletions
diff --git a/circuitpython/lib/mp3/examples/standalone/main.c b/circuitpython/lib/mp3/examples/standalone/main.c
new file mode 100644
index 0000000..9120424
--- /dev/null
+++ b/circuitpython/lib/mp3/examples/standalone/main.c
@@ -0,0 +1,128 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include "mp3dec.h"
+
+#define MAX_BUFFER_LEN (MAX_NSAMP * MAX_NGRAN * MAX_NCHAN)
+
+int16_t audiodata[MAX_BUFFER_LEN];
+
+typedef struct {
+    char *ptr, *end;
+} stream;
+#define READ_PTR(stream) ((void*)((stream)->ptr))
+#define BYTES_LEFT(stream) ((stream)->end - (stream)->ptr)
+#define CONSUME(stream, n) ((stream)->ptr += n)
+
+void skip_id3v2(stream* self) {
+    if (BYTES_LEFT(self) < 10) {
+        return;
+    }
+    uint8_t *data = READ_PTR(self);
+    if (!(
+            data[0] == 'I' &&
+            data[1] == 'D' &&
+            data[2] == '3' &&
+            data[3] != 0xff &&
+            data[4] != 0xff &&
+            (data[5] & 0x1f) == 0 &&
+            (data[6] & 0x80) == 0 &&
+            (data[7] & 0x80) == 0 &&
+            (data[8] & 0x80) == 0 &&
+            (data[9] & 0x80) == 0)) {
+        return;
+    }
+    uint32_t size = (data[6] << 21) | (data[7] << 14) | (data[8] << 7) | (data[9]);
+    size += 10; // size excludes the "header" (but not the "extended header")
+    CONSUME(self, size + 10);
+}
+
+bool mp3file_find_sync_word(stream* self) {
+    int offset = MP3FindSyncWord(READ_PTR(self), BYTES_LEFT(self));
+    if (offset >= 0) {
+        CONSUME(self, offset);
+        return true;
+    }
+    return false;
+}
+
+void fatal(const char *msg) { fprintf(stderr, "%s\n", msg); exit(1); }
+void perror_fatal(const char *msg) { perror(msg); exit(1); }
+
+bool probable_overflow(int16_t a, int16_t b) {
+    if(a > 32700 && b < -32700) {
+        return true;
+    } else if(b > 32700 && a < -32700) {
+        return true;
+    } else {
+        return false;
+    }
+}
+
+void look_for_overflow(int16_t *ptr, size_t os, int frame) {
+    for(size_t i=2; i<os; i+=2) {
+        int16_t l_old = ptr[i-2];
+        int16_t l_new = ptr[i];
+        int16_t r_old = ptr[i-1];
+        int16_t r_new = ptr[i+1];
+
+        if(probable_overflow(l_old, l_new)) {
+            printf("probable overflow, left  channel,  frame %5d sample %5d, %5d\n", frame, (i/2)-1, i/2);
+            printf("Consecutive sample values: %5d %5d\n", l_old, l_new);
+        }
+        if(probable_overflow(r_old, r_new)) {
+            printf("probable overflow, right channel,  frame %5d sample %5d, %5d\n", frame, (i/2)-1, i/2);
+            printf("Consecutive sample values: %5d %5d\n", r_old, r_new);
+        }
+    }
+}
+
+int main(int argc, char **argv) {
+    if(argc != 3) {
+        fprintf(stderr, "Decode MP3 into headerless LE16 stereo\n");
+        fprintf(stderr, "Usage: %s input.mp3 output.bin\n", argv[0]);
+        exit(99);
+    }
+
+    HMP3Decoder decoder = MP3InitDecoder();
+
+    FILE *fi = fopen(argv[1], "rb");
+    if(!fi) perror_fatal("open");
+
+    struct stat st;
+    if(fstat(fileno(fi), &st) < 0) perror_fatal("fstat");
+
+    stream s;
+    s.ptr = malloc(st.st_size);
+    if(!s.ptr) perror_fatal("malloc");
+    s.end = s.ptr + st.st_size;
+
+    if(fread(s.ptr, 1, st.st_size, fi) != st.st_size) perror_fatal("fread");
+
+    FILE *fo = fopen(argv[2], "wb");
+    if(!fo) perror_fatal("open");
+    
+    skip_id3v2(&s);
+
+    int frame=0;
+    while(mp3file_find_sync_word(&s)) {
+        MP3FrameInfo fi;
+        int err = MP3GetNextFrameInfo(decoder, &fi, READ_PTR(&s));
+        if(err != ERR_MP3_NONE) fatal("MP3GetNextFrameInfo");
+        int bytes_left = (int)BYTES_LEFT(&s);
+        uint8_t *inbuf = READ_PTR(&s);
+        err = MP3Decode(decoder, &inbuf, &bytes_left,
+                audiodata, 0);
+        if(err != ERR_MP3_NONE) fatal("MP3Decode");
+        look_for_overflow(audiodata, fi.outputSamps, ++frame);
+        if(fwrite(audiodata, 1, fi.outputSamps*sizeof(int16_t), fo)
+                != fi.outputSamps*sizeof(int16_t))
+            perror_fatal("fwrite");
+        CONSUME(&s, BYTES_LEFT(&s) - bytes_left); 
+    }
+
+    return 0;
+}