readme: Note: This recipe is trained with the codes from this PR https://github.com/k2-fsa/icefall/pull/399
  # Pre-trained Transducer-Stateless5 models for the AISHELL4 dataset with icefall.
  The model was trained on the far data of [AISHELL4](https://www.openslr.org/111) with the scripts in [icefall](https://github.com/k2-fsa/icefall) based on the latest version k2.  
  ## Training procedure
  The main repositories are list below, we will update the training and decoding scripts with the update of version.  
  k2: https://github.com/k2-fsa/k2 
  icefall: https://github.com/k2-fsa/icefall 
  lhotse: https://github.com/lhotse-speech/lhotse
  * Install k2 and lhotse, k2 installation guide refers to https://k2.readthedocs.io/en/latest/installation/index.html, lhotse refers to https://lhotse.readthedocs.io/en/latest/getting-started.html#installation. I think the latest version would be ok. And please also install the requirements listed in icefall.
  * Clone icefall(https://github.com/k2-fsa/icefall) and check to the commit showed above.
  ```
  git clone https://github.com/k2-fsa/icefall
  cd icefall
  ```
  * Preparing data.
  ```
  cd egs/aishell4/ASR
  bash ./prepare.sh
  ```
  * Training
  ```
  export CUDA_VISIBLE_DEVICES="0,1,2,3"
  ./pruned_transducer_stateless5/train.py \
                    --world-size 4 \
                    --num-epochs 30 \
                    --start-epoch 1 \
                    --exp-dir pruned_transducer_stateless5/exp \
                    --lang-dir data/lang_char \
                    --max-duration 220
  ```
  ## Evaluation results
  The decoding results (CER%) on AISHELL4(test) are listed below:
  
  When use-averaged-model=False, the CERs are
  
  |                                    |    test    | comment                                  |
  |------------------------------------|------------|------------------------------------------|
  |          greedy search             | 30.05      | --epoch 30, --avg 25, --max-duration 800 |
  | modified beam search (beam size 4) | 29.16      | --epoch 30, --avg 25, --max-duration 800 |
  | fast beam search (set as default)  | 29.20      | --epoch 30, --avg 25, --max-duration 1500|
  
  When use-averaged-model=True, the CERs are
  
  |                                    |    test    | comment                                                              |
  |------------------------------------|------------|----------------------------------------------------------------------|
  |          greedy search             | 29.89      | --iter 36000, --avg 8, --max-duration 800  --use-averaged-model=True |
  | modified beam search (beam size 4) | 28.91      | --iter 36000, --avg 8, --max-duration 800  --use-averaged-model=True |
  | fast beam search (set as default)  | 29.08      | --iter 36000, --avg 8, --max-duration 1500 --use-averaged-model=True |
  
  