[Fix] Introduce audio channels spec (#31595)

Signed-off-by: Jeremy Teboul <jeremyte@meta.com>

vllm/model_executor/models/qwen2_audio.py

@@ -140,6 +140,10 @@ class Qwen2AudioProcessingInfo(BaseProcessingInfo):
         assert isinstance(feature_extractor, WhisperFeatureExtractor)
         return feature_extractor
 
+    def get_target_channels(self) -> int:
+        """Return target audio channels for Qwen2 Audio models (mono)."""
+        return 1
+
     def get_supported_mm_limits(self) -> Mapping[str, int | None]:
         return {"audio": None}
 
@@ -201,7 +205,10 @@ class Qwen2AudioMultiModalDataParser(MultiModalDataParser):
 class Qwen2AudioMultiModalProcessor(BaseMultiModalProcessor[Qwen2AudioProcessingInfo]):
     def _get_data_parser(self) -> MultiModalDataParser:
         feature_extractor = self.info.get_feature_extractor()
-        return Qwen2AudioMultiModalDataParser(target_sr=feature_extractor.sampling_rate)
+        return Qwen2AudioMultiModalDataParser(
+            target_sr=feature_extractor.sampling_rate,
+            target_channels=self.info.get_target_channels(),
+        )
 
     def _call_hf_processor(
         self,