FIx Bark batching feature (#27271)

* fix bark batching

* make style

* add tests and make style

tests/models/bark/test_modeling_bark.py

@@ -1067,6 +1067,37 @@ class BarkModelIntegrationTests(unittest.TestCase):
             self.model.generate(**input_ids, do_sample=True, temperature=0.6, penalty_alpha=0.6)
             self.model.generate(**input_ids, do_sample=True, temperature=0.6, num_beams=4)
 
+    @slow
+    def test_generate_batching(self):
+        args = {"do_sample": False, "temperature": None}
+
+        s1 = "I love HuggingFace"
+        s2 = "In the light of the moon, a little egg lay on a leaf"
+        voice_preset = "en_speaker_6"
+        input_ids = self.processor([s1, s2], voice_preset=voice_preset).to(torch_device)
+
+        # generate in batch
+        outputs, audio_lengths = self.model.generate(**input_ids, **args, return_output_lengths=True)
+
+        # generate one-by-one
+        s1 = self.processor(s1, voice_preset=voice_preset).to(torch_device)
+        s2 = self.processor(s2, voice_preset=voice_preset).to(torch_device)
+        output1 = self.model.generate(**s1, **args)
+        output2 = self.model.generate(**s2, **args)
+
+        # up until the coarse acoustic model (included), results are the same
+        # the fine acoustic model introduces small differences
+        # first verify if same length (should be the same because it's decided in the coarse model)
+        self.assertEqual(tuple(audio_lengths), (output1.shape[1], output2.shape[1]))
+
+        # then assert almost equal
+        self.assertTrue(torch.allclose(outputs[0, : audio_lengths[0]], output1.squeeze(), atol=2e-3))
+        self.assertTrue(torch.allclose(outputs[1, : audio_lengths[1]], output2.squeeze(), atol=2e-3))
+
+        # now test single input with return_output_lengths = True
+        outputs, _ = self.model.generate(**s1, **args, return_output_lengths=True)
+        self.assertTrue((outputs == output1).all().item())
+
     @slow
     def test_generate_end_to_end_with_sub_models_args(self):
         input_ids = self.inputs