fftSamples shouldn't scale the spectrogram image

[wxfred]

Bug description

On the page https://wavesurfer.xyz/examples/?spectrogram.js, set the Spectrogram plugin option fftSamples from 1024 to 128 (or others), the height of the spectrogram image will change.

Environment

• Browser: Chrome

Expected result

The fftSamples parameter only affects the resolution of the image, not its height.
I think the final image should be stretched to cover the whole range.
If the sample rate is 48000Hz, the image should always cover 0 - 24000Hz, independent of fftSamples.
The lower fftSamples means the highlights in the image will be more blur, more like a mosaic effect.

Screenshots