examples: add LangChain integration guide (FunASR as agent tool)

Author: LauraGPT

examples/langchain/README.md

@@ -0,0 +1,83 @@
+# FunASR + LangChain Integration
+
+Use FunASR as a speech-to-text tool in your LangChain agents. Since FunASR exposes an OpenAI-compatible API, integration is straightforward.
+
+## Setup
+
+```bash
+# Start FunASR server
+pip install torch torchaudio
+pip install funasr vllm fastapi uvicorn python-multipart
+funasr-server --device cuda
+
+# Install LangChain
+pip install langchain langchain-openai
+```
+
+## As a LangChain Tool
+
+```python
+from langchain.tools import tool
+from openai import OpenAI
+
+asr_client = OpenAI(base_url="http://localhost:8000/v1", api_key="unused")
+
+@tool
+def speech_to_text(audio_path: str) -> str:
+    """Transcribe an audio file to text using local FunASR.
+    Supports wav, mp3, flac. Returns transcribed text with speaker IDs."""
+    result = asr_client.audio.transcriptions.create(
+        model="fun-asr-nano",
+        file=open(audio_path, "rb"),
+        response_format="verbose_json"
+    )
+    return result.text
+
+
+# Use with any LangChain agent
+from langchain_openai import ChatOpenAI
+from langchain.agents import AgentExecutor, create_tool_calling_agent
+from langchain_core.prompts import ChatPromptTemplate
+
+llm = ChatOpenAI(model="gpt-4o")
+tools = [speech_to_text]
+prompt = ChatPromptTemplate.from_messages([
+    ("system", "You are a helpful assistant that can transcribe audio files."),
+    ("human", "{input}"),
+    ("placeholder", "{agent_scratchpad}"),
+])
+
+agent = create_tool_calling_agent(llm, tools, prompt)
+executor = AgentExecutor(agent=agent, tools=tools)
+result = executor.invoke({"input": "Please transcribe meeting.wav"})
+```
+
+## With Dify / AutoGen / CrewAI
+
+Any framework supporting OpenAI audio API connects directly:
+
+```python
+from openai import OpenAI
+client = OpenAI(
+    base_url="http://localhost:8000/v1",  # FunASR server
+    api_key="unused"
+)
+result = client.audio.transcriptions.create(
+    model="fun-asr-nano",
+    file=open("audio.wav", "rb")
+)
+```
+
+## Features
+
+- 50+ languages (Chinese dialects, English, Japanese, Korean...)
+- Speaker diarization (`spk=true`)
+- Word-level timestamps (`response_format="verbose_json"`)
+- Hotword boosting
+- 170x realtime, fully local, MIT license
+
+## Links
+
+- [FunASR GitHub](https://github.com/modelscope/FunASR)
+- [OpenAI API examples](../openai_api/)
+- [Website](https://www.funasr.com)