xiph opusfile support and taglib write support.

opusfile-decoder.rkt

@@ -24,9 +24,21 @@
   ;; Opus decode output is always 48 kHz PCM.  The original input rate, if
   ;; present in metadata, is not the actual decoder output rate.
 
-  (define libopusfile
-    (with-handlers ([exn:fail? (lambda (_) #f)])
-      (ffi-lib "libopusfile" '("0" #f))))
+
+  (define libogg (get-lib (case (system-type 'os)
+                                 [(windows) '("ogg")]
+                                 [else      '("ogg" "libogg")])
+                               '(#f)))
+
+  (define libopus (get-lib (case (system-type 'os)
+                             [(windows) '("opus")]
+                             [else      '("opus" "libopus")])
+                           '(#f)))
+  
+  (define libopusfile (get-lib (case (system-type 'os)
+                                 [(windows) '("opusfile")]
+                                 [else      '("opusfile" "libopusfile")])
+                               '(#f)))
 
   (define _OggOpusFile _pointer)
 
@@ -36,12 +48,16 @@
   (define (opusfile-output-format? v)
     (or (eq? v 's16) (eq? v 's24)))
 
-  (define current-opusfile-output-format
-    (make-parameter 's16
-      (lambda (v)
-        (unless (opusfile-output-format? v)
-          (raise-argument-error 'current-opusfile-output-format "(or/c 's16 's24)" v))
-        v)))
+  (define cur-output-format 's16)
+
+  (define (current-opusfile-output-format . args)
+    (unless (null? args)
+      (if (or (> (length args) 1)
+              (not (opusfile-output-format? (car args))))
+          (raise-argument-error 'current-opusfile-output-format
+                                "(or/c 's16 's24)")
+          (set! cur-output-format (car args))))
+    cur-output-format)
 
   (define (opus-bits-per-sample)
     (case (current-opusfile-output-format)