Improve UX around seeing audio wave forms.

- Attempts to generate the wave form on download instead on display
- Allows multi-threaded generation of wave forms instead of serial
  executor

app/src/main/java/org/thoughtcrime/securesms/audio/AudioFileInfo.java

@@ -0,0 +1,45 @@
+package org.thoughtcrime.securesms.audio;
+
+import androidx.annotation.NonNull;
+
+import com.google.protobuf.ByteString;
+
+import org.thoughtcrime.securesms.database.model.databaseprotos.AudioWaveFormData;
+
+import java.util.concurrent.TimeUnit;
+
+public class AudioFileInfo {
+  private final long    durationUs;
+  private final byte[]  waveFormBytes;
+  private final float[] waveForm;
+
+  public static @NonNull AudioFileInfo fromDatabaseProtobuf(@NonNull AudioWaveFormData audioWaveForm) {
+    return new AudioFileInfo(audioWaveForm.getDurationUs(), audioWaveForm.getWaveForm().toByteArray());
+  }
+
+  AudioFileInfo(long durationUs, byte[] waveFormBytes) {
+    this.durationUs    = durationUs;
+    this.waveFormBytes = waveFormBytes;
+    this.waveForm      = new float[waveFormBytes.length];
+
+    for (int i = 0; i < waveFormBytes.length; i++) {
+      int unsigned = waveFormBytes[i] & 0xff;
+      this.waveForm[i] = unsigned / 255f;
+    }
+  }
+
+  public long getDuration(@NonNull TimeUnit timeUnit) {
+    return timeUnit.convert(durationUs, TimeUnit.MICROSECONDS);
+  }
+
+  public float[] getWaveForm() {
+    return waveForm;
+  }
+
+  public @NonNull AudioWaveFormData toDatabaseProtobuf() {
+    return AudioWaveFormData.newBuilder()
+                            .setDurationUs(durationUs)
+                            .setWaveForm(ByteString.copyFrom(waveFormBytes))
+                            .build();
+  }
+}