NoBackendError: please add more details to the exception message

[slychief]

Hi,

I just spent 2 hours debugging, why audioread cannot find ffmpeg when everything else can see and access it.

It turned out, I was iterating over a directory and one of the files was not an audio file resulting in the NoBackendError, which is IMHO misleading. Could you please add a descriptive message to the exception? Something like "File xyz has a codec where no backend could be identified for".

Best,
Alex

[2020-02-04 14:58:34,366] ERROR in app: Exception on /upload [GET]
Traceback (most recent call last):
  File "C:\anaconda\envs\msd_demo\lib\site-packages\flask\app.py", line 2446, in wsgi_app
    response = self.full_dispatch_request()
  File "C:\anaconda\envs\msd_demo\lib\site-packages\flask\app.py", line 1951, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "C:\anaconda\envs\msd_demo\lib\site-packages\flask\app.py", line 1820, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "C:\anaconda\envs\msd_demo\lib\site-packages\flask\_compat.py", line 39, in reraise
    raise value
  File "C:\anaconda\envs\msd_demo\lib\site-packages\flask\app.py", line 1949, in full_dispatch_request
    rv = self.dispatch_request()
  File "C:\anaconda\envs\msd_demo\lib\site-packages\flask\app.py", line 1935, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "app.py", line 102, in upload
    ap.convert_audio(f["path"])
  File "C:\Work\Github\slychief\speechrec\audio_processing.py", line 48, in convert_audio
    wave_data = load_audio(src_name)
  File "C:\Work\Github\slychief\speechrec\audio_processing.py", line 44, in load_audio
    wave_data, sample_rate = librosa.core.load(f_name, sr=SAMPLE_RATE, mono=True)
  File "C:\anaconda\envs\msd_demo\lib\site-packages\librosa\core\audio.py", line 119, in load
    with audioread.audio_open(os.path.realpath(path)) as input_file:
  File "C:\anaconda\envs\msd_demo\lib\site-packages\audioread\__init__.py", line 116, in audio_open
    raise NoBackendError()
audioread.exceptions.NoBackendError

[sampsyo]

Sure; a wording clarification would be good idea! I'd be happy to accept a pull request that does something like that (as long as it's backwards-compatible).