add ffmpeg instruct

README.md

@@ -997,6 +997,30 @@ pip install "transformers==4.51.0" accelerate "torch>=2.3.0,<=2.8.0" "torchaudio
 pip install "transformers==4.51.0" accelerate "torch>=2.3.0,<=2.8.0" "torchaudio<=2.8.0" "minicpmo-utils[all]>=1.0.2"
 ```
 
+<details>
+<summary>Click to show FFmpeg installation instructions (optional).</summary>
+
+**Note:** FFmpeg is required for video frame extraction (`get_video_frame_audio_segments` with `use_ffmpeg=True`) and video generation (`generate_duplex_video`). For more information, visit the [official FFmpeg website](https://www.ffmpeg.org/).
+
+  **macOS (Homebrew):**
+
+  ```bash
+  brew install ffmpeg
+  ```
+
+  **Ubuntu/Debian:**
+
+  ```bash
+  sudo apt update && sudo apt install ffmpeg
+  ```
+
+  **Verify installation:**
+
+  ```bash
+  ffmpeg -version
+  ```
+</details>
+
 
 ### Model Initialization  <!-- omit in toc -->