[Whisper] Fix decoder ids methods (#20599)

* [Whisper] Fix decoder ids methods

* enum property

src/transformers/models/whisper/tokenization_whisper.py

@@ -583,5 +583,6 @@ class WhisperTokenizer(PreTrainedTokenizer):
         return input_ids
 
     def get_decoder_prompt_ids(self, task=None, language=None, no_timestamps=True):
-        self.set_prefix_tokens(task=task, language=language, predict_timestamps=no_timestamps)
-        return self.prefix_tokens
+        self.set_prefix_tokens(task=task, language=language, predict_timestamps=not no_timestamps)
+        forced_decoder_ids = [(rank + 1, token) for rank, token in enumerate(self.prefix_tokens)]
+        return forced_decoder_ids

tests/models/whisper/test_processor_whisper.py

@@ -26,6 +26,11 @@ if is_speech_available():
     from transformers import WhisperFeatureExtractor, WhisperProcessor
 
 
+START_OF_TRANSCRIPT = 50257
+TRANSCRIBE = 50358
+NOTIMESTAMPS = 50362
+
+
 @require_torch
 @require_torchaudio
 @require_sentencepiece
@@ -128,3 +133,17 @@ class WhisperProcessorTest(unittest.TestCase):
             feature_extractor.model_input_names,
             msg="`processor` and `feature_extractor` model input names do not match",
         )
+
+    def test_get_decoder_prompt_ids(self):
+        feature_extractor = self.get_feature_extractor()
+        tokenizer = self.get_tokenizer()
+
+        processor = WhisperProcessor(tokenizer=tokenizer, feature_extractor=feature_extractor)
+        forced_decoder_ids = processor.get_decoder_prompt_ids(task="transcribe", no_timestamps=True)
+
+        self.assertIsInstance(forced_decoder_ids, list)
+        for ids in forced_decoder_ids:
+            self.assertIsInstance(ids, (list, tuple))
+
+        expected_ids = [START_OF_TRANSCRIPT, TRANSCRIBE, NOTIMESTAMPS]
+        self.assertListEqual([ids[-1] for ids in forced_decoder_ids], expected_ids)