[Feature] WebSocket streaming audio input for ASR (#22848)

Co-authored-by: Yihao Wang <42559837+AgainstEntropy@users.noreply.github.com>

python/sglang/srt/entrypoints/http_server.py

@@ -54,6 +54,7 @@ from fastapi import (
     Query,
     Request,
     UploadFile,
+    WebSocket,
 )
 from fastapi.exceptions import RequestValidationError
 from fastapi.middleware.cors import CORSMiddleware
@@ -1605,6 +1606,17 @@ async def openai_v1_audio_transcriptions(
     )
 
 
+@app.websocket("/v1/realtime")
+async def openai_v1_realtime_transcription(ws: WebSocket):
+    """OpenAI Realtime transcription WebSocket endpoint."""
+    # /v1/realtime is OpenAI's unified Realtime URL covering transcription +
+    # chat modes. This handler implements the transcription subset only;
+    # chat-mode session.update payloads are rejected by the
+    # `Literal["transcription"]` constraint on TranscriptionSessionConfig.type
+    # (see realtime/protocol.py).
+    await ws.app.state.openai_serving_transcription.handle_websocket(ws)
+
+
 @app.get("/v1/models", response_class=ORJSONResponse)
 async def available_models():
     """Show available models. OpenAI-compatible endpoint."""