LÖVE

i dont know why but when i try to do it keeps returning 0 (even though there is actually sound playing)

Hi welcome to the forums. With that information there's very little anyone can do to help. I can only suggest you to double check that the audio corresponds to the soundData.

Edit: Maybe also check that it's a stereo track and that the second channel has data.

The unit returned by Source:tell is seconds by default, whereas SoundData:getSample takes a sample index. You can use Source:tell("samples") to get the current playback position of the Source in the same unit that SoundData:getSample needs.