add blank_penalty for online transducer (#548)

python-api-examples/speech-recognition-from-microphone.py

@@ -111,6 +111,17 @@ def get_args():
         """,
     )
 
+    parser.add_argument(
+        "--blank-penalty",
+        type=float,
+        default=0.0,
+        help="""
+        The penalty applied on blank symbol during decoding.
+        Note: It is a positive value that would be applied to logits like
+        this `logits[:, 0] -= blank_penalty` (suppose logits.shape is
+        [batch_size, vocab] and blank id is 0).
+        """,
+    )
 
     return parser.parse_args()
 
@@ -136,6 +147,7 @@ def create_recognizer(args):
         provider=args.provider,
         hotwords_file=args.hotwords_file,
         hotwords_score=args.hotwords_score,
+        blank_penalty=args.blank_penalty,
     )
     return recognizer