padding.patch

~/W/v/cljs-audio-utils (jannis/mp3-encoder) $ git diff
diff --git a/src/devcards/audio_utils/devcards/mp3_encoder.cljs b/src/devcards/audio_utils/devcards/mp3_encoder.cljs
index 5a5813f..121651a 100644
--- a/src/devcards/audio_utils/devcards/mp3_encoder.cljs
+++ b/src/devcards/audio_utils/devcards/mp3_encoder.cljs
@@ -72,11 +72,15 @@
     (reduce (fn [length-so-far buf]
               (doseq [channel (range 0 (.-numberOfChannels buffer))]
                 (let [in-chan  (.getChannelData buf channel)
-                      out-chan (.getChannelData buffer channel)]
-                  (doseq [n (range 0 (.-length in-chan))]
-                    (aset out-chan (+ length-so-far n)
+                      out-chan (.getChannelData buffer channel)
+                      padding  4410]
+                  (doseq [n (range padding (- (.-length in-chan)
+                                              (* 2 padding)))]
+                    (aset out-chan (+ length-so-far (- n padding))
                           (aget in-chan n)))))
-              (+ length-so-far (.-length buf)))
+              (+ length-so-far
+                 (- (.-length buf)
+                    (* 2 padding))))
             0 buffers)
     buffer))
 
diff --git a/src/main/audio_utils/mp3_encoder.cljs b/src/main/audio_utils/mp3_encoder.cljs
index 97b80c3..9b41d4b 100644
--- a/src/main/audio_utils/mp3_encoder.cljs
+++ b/src/main/audio_utils/mp3_encoder.cljs
@@ -11,8 +11,11 @@
     (reset! next nil))
 
   (process-audio [this data]
-    (let [int-data (mapv (fn [samples]
-                           (into-array (map #(* 32768 %) samples)))
+    (let [padding  4410
+          int-data (mapv (fn [samples]
+                           (into-array (concat (repeat padding 0)
+                                               (map #(* 32768 %) samples)
+                                               (repeat padding 0))))
                          data)
           encoder  (js/lamejs.Mp3Encoder. 2 sample-rate bit-rate)
           encoded  #js []]