The line is here debug link 1
The data I use is Aishell-1, which is a Chinese ASR coupus.
the pre-trained model is  pretrained model
btw, it seems that ctc just predict blank is a frequent problem，here are some examples raised by others
ctc problem 1
ctc problem
ctc problem
Some answers said that ctc learn blank firstly and then turn to learn commot characters. I don’t know whether such interpretation is ture or not.
perhaps, in fact, I use a huge vocab including 8000+ Chinese characters and train data only have 170h,the model was hard to be trained?