[Misc] Raise error for missing video metadata in `MultiModalDataParser` (#27664)

Signed-off-by: Isotr0py <mozf@mail2.sysu.edu.cn>
Signed-off-by: Isotr0py <2037008807@qq.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

vllm/multimodal/parse.py

@@ -506,6 +506,11 @@ class MultiModalDataParser:
         for data_item in data_items:
             video, metadata = self._get_video_with_metadata(data_item)
             if self.video_needs_metadata:
+                if metadata is None:
+                    raise ValueError(
+                        "Video metadata is required but not found in mm input. "
+                        "Please check your video input in `multi_modal_data`"
+                    )
                 new_videos.append((video, metadata))
                 metadata_lst.append(metadata)
             else: