Added capability information

audio-decoder.rkt

@@ -10,6 +10,7 @@
            racket/contract
            racket/string
            racket/path
+           racket-mimetypes
            )
 
   (provide audio-open
@@ -24,6 +25,8 @@
            make-audio-reader
            audio-handle?
            audio-supported-extensions
+           audio-supported-formats
+           audio-decoder-for-extension
            current-opusfile-output-format
            opusfile-output-format?
            )
@@ -107,6 +110,20 @@
   (define (audio-supported-extensions)
     known-extensions)
 
+  (define/contract (audio-supported-formats)
+    (-> (listof
+         (cons/c string?
+                 string?)))
+    (for/list ((extension
+                (in-list known-extensions)))
+      (cons
+       extension
+       (mimetype-for-ext
+        (string-append "audio."
+                       extension)
+        #:default
+        "application/octet-stream"))))
+
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;; Register audio reader
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
@@ -268,6 +285,14 @@
            (cons 'wma 'ffmpeg)
            (cons 'matroska 'ffmpeg))))
 
+  (define/contract (audio-decoder-for-extension extension)
+    (-> (or/c string? symbol?)
+        (or/c #f symbol?))
+    (hash-ref
+     reader-for-kind
+     (audio-format-for-extension extension)
+     #f))
+
 
 
   (define (find-reader audio-file)

audio-placed-player.rkt

@@ -414,7 +414,8 @@
         (audio-seek ao-dec percentage)))
 
     (define (volume percentage)
-      (set! req-volume percentage))
+      (set! req-volume percentage)
+      (check-volume))
 
     (define (ao-buf-ms)
       (ao-playback-buf-ms))

audio-sniffer.rkt

@@ -10,6 +10,7 @@
          audio-sniff-format
          audio-sniff-format/extension
          audio-sniff-extension
+         audio-format-for-extension
          audio-format-matches?
          audio-format-known?)
 
@@ -46,6 +47,30 @@
              (substring s 1)
              s))])))
 
+(define (audio-format-for-extension* extension)
+  (let* ((text (string-downcase
+                (format "~a" extension)))
+         (normalized
+          (if (string-prefix? text ".")
+              (substring text 1)
+              text)))
+    (case (string->symbol normalized)
+      [(mp3 mp2 mp1) 'mp3]
+      [(flac) 'flac]
+      [(ogg oga) 'ogg]
+      [(opus) 'opus]
+      [(wav wave) 'wav]
+      [(aif aiff aifc) 'aiff]
+      [(m4a mp4 m4b m4p) 'mp4]
+      [(aac) 'aac]
+      [(alac) 'alac]
+      [(ac3) 'ac3]
+      [(ape) 'ape]
+      [(wv wvp wvpk wavpack) 'wavpack]
+      [(wma asf) 'wma]
+      [(webm mka mkv) 'matroska]
+      [else 'unknown])))
+
 (define (file-readable-status file)
   (cond
     [(not (file-exists? file)) 'file-not-found]
@@ -294,22 +319,9 @@
        fmt]
       [(not (eq? fmt 'unknown)) fmt]
       [else
-       (case (string->symbol (or (audio-sniff-extension* file) ""))
+       (audio-format-for-extension*
-         [(mp3 mp2 mp1) 'mp3]
+        (or (audio-sniff-extension* file)
-         [(flac) 'flac]
+            ""))])))
-         [(ogg oga) 'ogg]
-         [(opus) 'opus]
-         [(wav wave) 'wav]
-         [(aif aiff aifc) 'aiff]
-         [(m4a mp4 m4b m4p) 'mp4]
-         [(aac) 'aac]
-         [(alac) 'alac]
-         [(ac3) 'ac3]
-         [(ape) 'ape]
-         [(wv wvp wvpk wavpack) 'wavpack]
-         [(wma asf) 'wma]
-         [(webm mka mkv) 'matroska]
-         [else 'unknown])])))
 
 (define (audio-format-known?* fmt)
   (not (eq? (memq fmt audio-formats) #f)))
@@ -321,6 +333,10 @@
   (-> path-string? (or/c string? #f))
   (audio-sniff-extension* file))
 
+(define/contract (audio-format-for-extension extension)
+  (-> (or/c string? symbol?) audio-format?)
+  (audio-format-for-extension* extension))
+
 (define/contract (audio-sniff-format file)
   (-> path-string? audio-format?)
   (audio-sniff-format* file))

info.rkt

@@ -15,6 +15,7 @@
   '("racket/gui" "racket/base" "racket"
                  "finalizer" "draw-lib" "net-lib"
                  "simple-log" "simple-ini" "racket-sprintf"
+                 "racket-mimetypes"
                  "early-return" "let-assert"
                  "uni-channel" "port-channel"
                  "rackunit-lib"

main.rkt

@@ -3,12 +3,19 @@
 (require "taglib.rkt"
          "audio-sniffer.rkt"
          "audio-player.rkt"
+         (only-in "audio-decoder.rkt"
+                  audio-supported-extensions
+                  audio-supported-formats
+                  audio-decoder-for-extension)
          "opusfile-decoder.rkt"
          )
 
 (provide (all-from-out "taglib.rkt")
          (all-from-out "audio-sniffer.rkt")
          (all-from-out "audio-player.rkt")
+         audio-supported-extensions
+         audio-supported-formats
+         audio-decoder-for-extension
          current-opusfile-output-format
          opusfile-output-format?
          )

scrbl/audio-decoder.scrbl

@@ -105,6 +105,24 @@ Returns the current list of supported filename extensions. This is the
 same list returned by @racket[audio-known-exts?].
 }
 
+@defproc[(audio-supported-formats)
+         (listof (cons/c string? string?))]{
+
+Returns the supported filename extensions together with the MIME type
+reported by @racketmodname[racket-mimetypes]. Unknown MIME types use
+@racket["application/octet-stream"].
+}
+
+@defproc[(audio-decoder-for-extension
+          [extension (or/c string? symbol?)])
+         (or/c #f symbol?)]{
+
+Returns the decoder selected for audio with @racket[extension], such as
+@racket['flac], @racket['opusfile], or @racket['ffmpeg]. The result is
+@racket[#f] when the extension is not recognized. Actual playback still
+sniffs the file contents before selecting its decoder.
+}
+
 @section{Built-in decoder selection}
 
 The built-in decoder table contains:

tests/capabilities-test.rkt

@@ -0,0 +1,32 @@
+#lang racket/base
+
+(require rackunit
+         racket-audio)
+
+(define formats
+  (audio-supported-formats))
+
+(check-not-false
+ (member "flac"
+         (audio-supported-extensions)))
+(check-equal?
+ (cdr (assoc "flac" formats))
+ "audio/x-flac")
+(check-eq?
+ (audio-decoder-for-extension "flac")
+ 'flac)
+(check-eq?
+ (audio-decoder-for-extension ".mp3")
+ 'ffmpeg)
+(check-not-false
+ (member (audio-decoder-for-extension 'opus)
+         '(opusfile ffmpeg)))
+(check-false
+ (audio-decoder-for-extension "not-audio"))
+
+(for ((extension
+       (in-list
+        (audio-supported-extensions))))
+  (check-true
+   (symbol?
+    (audio-decoder-for-extension extension))))