libsox.patch

--- src/formats.c	2014-10-27 02:55:50.000000000 +0000
+++ src/formats_new.c	2020-11-18 19:14:17.398689371 +0000
@@ -91,6 +91,21 @@
 
   if (ext && !strcasecmp(ext, "snd"))
   CHECK(sndr  , 7, 1, ""     , 0,  2, "\0")
+
+#if defined HAVE_MP3 && (defined STATIC_MP3 || !defined HAVE_LIBLTDL)
+  // http://www.mp3-tech.org/programmer/frame_header.html
+  // Check the first two bytes are
+  // expected             1111_1111 111X_X01X
+  // mask         \xEEE6 (1111_1111 1110_0110)
+  // masked value \xEEE2 (1111_1111 1110_0010)
+  if (len >= 2 && !memcmp(data, "\xFF", 1)) {
+    unsigned char second_byte = data[1];
+    unsigned char mask = 0xE6;
+    unsigned char expected = 0xE2;
+    if ((second_byte & mask) == expected)
+      return "mp3";
+  }
+#endif
   #undef CHECK
 
 #if HAVE_MAGIC