@MainThread
  public void playAnimation() {
    running = true;
    notifyStart(isReversed());
    setFrame((int) (isReversed() ? getMaxFrame() : getMinFrame()));
    lastFrameTimeNs = 0;
    repeatCount = 0;
    postFrameCallback();
  }
Returns the current speed. This will be affected by repeat mode REVERSE.
lottie/src/main/java/com/airbnb/lottie/utils/LottieValueAnimator.java