Created by: chenjiasheng

https://github.com/PaddlePaddle/models/blob/8b5c739a847b03ae8e7daa10f5311ef8cd12290b/deep_speech_2/model_utils/decoder.py#L87

If vocabulary dosen't contain blank, we have:

vocabulary=['a', 'b', ..., 'z', ' ', '.']
len(vocabulary) = 28
len(prob_list) = 29

Then at line 135,

new_char = vocabulary[c]

here c ranges from 0 to len(prob_list), but vocabulary[28] causes index out of range.

To use this decoder, one have to make the vocabulary a dict indexed from 1 instead of a list indexed from 0, in spite of that the doc suggests vocabulary to be a list.

    :param vocabulary: Vocabulary list.
    :type vocabulary: list

This is really confusing.

@xinghai-sun @kuke