You can then listen to the result:

from IPython.display import Audio
Audio(output['audio'], rate=output['sampling_rate']) 

Run inference manually
You can achieve the same inference results without using the pipeline, however, more steps will be required. 
Load the model from the 🤗 Hub: 

model = SpeechT5ForTextToSpeech.from_pretrained("YOUR_ACCOUNT/speecht5_finetuned_voxpopuli_nl")

Pick an example from the test dataset obtain a speaker embedding.