Don't update duration if last timestamp is same as begin (#191)

whisper/transcribe.py

@@ -220,7 +220,7 @@ def transcribe(
             else:
                 duration = segment_duration
                 timestamps = tokens[timestamp_tokens.nonzero().flatten()]
-                if len(timestamps) > 0:
+                if len(timestamps) > 0 and timestamps[-1].item() != tokenizer.timestamp_begin:
                     # no consecutive timestamps but it has a timestamp; use the last one.
                     # single timestamp at the end means no speech after the last timestamp.
                     last_timestamp_position = timestamps[-1].item() - tokenizer.timestamp_begin