Librispeech documentation, clarification on format
https://github.com/huggingface/datasets/blob/cd3ce34ab1604118351e1978d26402de57188901/datasets/librispeech_asr/librispeech_asr.py#L53

> Note that in order to limit the required storage for preparing this dataset, the audio
> is stored in the .flac format and is not converted to a float32 array. To convert, the audio
> file to a float32 array, please make use of the `.map()` function as follows:
> 
> ```python
> import soundfile as sf
> def map_to_array(batch):
>     speech_array, _ = sf.read(batch["file"])
>     batch["speech"] = speech_array
>     return batch
> dataset = dataset.map(map_to_array, remove_columns=["file"])
> ```

Is this still true?

In my case, `ds["train.100"]` returns:
```
Dataset({
    features: ['file', 'audio', 'text', 'speaker_id', 'chapter_id', 'id'],
    num_rows: 28539
})
```
and taking the first instance yields:
```
{'file': '374-180298-0000.flac',
 'audio': {'path': '374-180298-0000.flac',
  'array': array([ 7.01904297e-04,  7.32421875e-04,  7.32421875e-04, ...,
         -2.74658203e-04, -1.83105469e-04, -3.05175781e-05]),
  'sampling_rate': 16000},
 'text': 'CHAPTER SIXTEEN I MIGHT HAVE TOLD YOU OF THE BEGINNING OF THIS LIAISON IN A FEW LINES BUT I WANTED YOU TO SEE EVERY STEP BY WHICH WE CAME I TO AGREE TO WHATEVER MARGUERITE WISHED',
 'speaker_id': 374,
 'chapter_id': 180298,
 'id': '374-180298-0000'}
```

The `audio` `array` seems to be already decoded. So such convert/decode code as mentioned in the doc is wrong?

But I wonder, is it actually stored as flac on disk, and the decoding is done on-the-fly? Or was it decoded already during the preparation and is stored as raw samples on disk?

Note that I also used `datasets.load_dataset("librispeech_asr", "clean").save_to_disk(...)` and then `datasets.load_from_disk(...)` in this example. Does this change anything on how it is stored on disk?

A small related question: Actually I would prefer to even store it as mp3 or ogg on disk. Is this easy to convert?