How to execute tf.signal.stft?

Hi,

i am trying to get the result of tf.signal.stft, eg.

test_stft = tf.math.log(tf.abs(tf.signal.stft(test,frame_length=512,frame_step=128))) 

I thought in eager execution it will give me the result, but all i get is:

 tf.Tensor([], shape=(20000, 0, 257), dtype=float32) 

What can I do, to get Tensorflow to finally calcuate the result. I have trouble to understand EagerMode and GraphMode. Maybe a good Youtube resource may also help.