The time required to analyze the audio content of a file and generate its waveform can be affected by several factors. The most relevant one is the size of the file. Since WavePlayer needs to fully load an audio file in order to analyze its content and generate a waveform, the longer is the audio track, the longer it will take it to generate its waveform. Usually, we consider that it takes 1 or 2 seconds per minute of audio recording. So, for example, the waveform of a 5-minute track should render in 5 to 10 seconds.
Of course, also a higher bitrate will affect the time required to generate a waveform.