decode mp3 with librosa if torchaudio is > 0.12 as a temporary workaround 
_The documentation is not available anymore as the PR was closed or merged._ Thanks ! Should we still support torchaudio>0.12 if it works ? And if it doesn't we can explain that downgrading is the right solution, or alternatively use librosa @lhoestq 

> Should we still support torchaudio>0.12 if it works ? And if it doesn't we can explain that downgrading is the right solution, or alternatively use librosa

I'm not sure here, because from the one hand, if `torchaudio` works - it works 60 times faster then `librosa`.
But from the other hand, we will get inconsistent behavior (=different results of decoding) for users of `torchaudio>=0.12`. 
I'd better go for using `librosa` only to avoid inconsistency then. wdyt? It seems a bit too constraining to not allow users who have a working torchaudio 0.12 setup to not use it. 

If the issue is about avoiding silent errors if the decoding changes, maybe we can log which back-end is used ? It can even be a warning with performance suggestions ("you're using librosa but torchaudio 0.xx is recommended").

Note that users can still have a requirements.txt or whatever in their projects if they really want full reproducibility (and it's the bare minimum imo)

There are multiple possible back-ends so it's maybe not reasonable to only allow one back-end, especially since each back-end has installation constrains and there's no "best" back-end. Woohoo all green ! Feel free to merge if it's all good for you :)
`torchaudio>0.12` fails with decoding mp3 files if `ffmpeg<4`. currently we ask users to downgrade torchaudio, but sometimes it's not possible as torchaudio version is binded to torch version. as a temporary workaround we can decode mp3 with librosa (though it 60 times slower, at least it works)

another option would be to ask users to install the required version of `ffmpeg`, but is non-trivial on colab: it's not in apt packages in ubuntu 18 and `conda` is not preinstalled (with `conda` it would be easily installable)

- [x] decode with torchaudio anyway if the version of ffmpeg is correct? it's 60 times faster
- [x] tests 
- [x] DO NOT FORGET to get back all the tests

see https://github.com/huggingface/datasets/issues/4776 and https://github.com/huggingface/datasets/issues/3663#issuecomment-1225797165 (there is a Colab notebook to reproduce the error)