Add support for .ogg, .flac, .aac, and others

Instead of throwing an error, unknown audio formats will be interpreted
by the system's AudioContext and encoded as a wav instead.
File sizes are pretty bad, but this is still net improvement.
ScratchAddons/ScratchAddons#6515 (comment)

src/containers/sound-tab.jsx

@@ -230,7 +230,7 @@ class SoundTab extends React.Component {
                     title: intl.formatMessage(messages.fileUploadSound),
                     img: fileUploadIcon,
                     onClick: this.handleFileUploadClick,
-                    fileAccept: '.wav, .mp3',
+                    fileAccept: '.wav, .mp3, .ogg, .flac, .aac',
                     fileChange: this.handleSoundUpload,
                     fileInput: this.setFileInput,
                     fileMultiple: true

src/lib/file-uploader.js

@@ -3,6 +3,7 @@ import randomizeSpritePosition from './randomize-sprite-position.js';
 import bmpConverter from './bmp-converter';
 import gifDecoder from './gif-decoder';
 import fixSVG from './tw-svg-fixer';
+import convertAudioToWav from './tw-convert-audio-wav.js';
 
 /**
  * Extract the file name given a string of the form fileName + ext
@@ -211,7 +212,11 @@ const soundUpload = function (fileData, fileType, storage, handleSound, handleEr
         break;
     }
     default:
-        handleError(`Encountered unexpected file type: ${fileType}`);
+        convertAudioToWav(fileData)
+            .then(fixed => {
+                soundUpload(fixed, 'audio/wav', storage, handleSound, handleError);
+            })
+            .catch(handleError);
         return;
     }
 

src/lib/tw-convert-audio-wav.js

@@ -0,0 +1,21 @@
+import SharedAudioContext from './audio/shared-audio-context';
+import WavEncoder from 'wav-encoder';
+
+const convertAudioToWav = fileData => {
+    /** @type {AudioContext} */
+    const audioContext = new SharedAudioContext();
+
+    return audioContext.decodeAudioData(fileData)
+        .then(decodedData => {
+            const channels = [];
+            for (let i = 0; i < decodedData.numberOfChannels; i++) {
+                channels.push(decodedData.getChannelData(i));
+            }
+            return WavEncoder.encode({
+                sampleRate: decodedData.sampleRate,
+                channelData: channels
+            });
+        });
+};
+
+export default convertAudioToWav;