dont re-prepare voice messages (#7897)

* dont reprepare voice messages

Signed-off-by: Kerry Archibald <kerrya@element.io>

* remove debug

Signed-off-by: Kerry Archibald <kerrya@element.io>

* test Playback

Signed-off-by: Kerry Archibald <kerrya@element.io>

* test RecordingPlayback

Signed-off-by: Kerry Archibald <kerrya@element.io>

* forgotten copyright

Signed-off-by: Kerry Archibald <kerrya@element.io>

* add comments

Signed-off-by: Kerry Archibald <kerrya@element.io>

src/audio/Playback.ts

@@ -133,6 +133,13 @@ export class Playback extends EventEmitter implements IDestroyable {
     }
 
     public async prepare() {
+        // don't attempt to decode the media again
+        // AudioContext.decodeAudioData detaches the array buffer `this.buf`
+        // meaning it cannot be re-read
+        if (this.state !== PlaybackState.Decoding) {
+            return;
+        }
+
         // The point where we use an audio element is fairly arbitrary, though we don't want
         // it to be too low. As of writing, voice messages want to show a waveform but audio
         // messages do not. Using an audio element means we can't show a waveform preview, so