[Realtime] Introduce Media Transport Adapters

src/content/docs/realtime/sfu/media-transport-adapters/index.mdx

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+---
+pcx_content_type: navigation
+title: Media Transport Adapters
+sidebar:
+  order: 6
+  group:
+    label: Adapters
+---
+
+import { Render } from "~/components";
+
+Media Transport Adapters bridge WebRTC and other transport protocols. Adapters handle protocol conversion, codec transcoding, and bidirectional media flow between WebRTC sessions and external endpoints.
+
+## What adapters do
+
+Adapters extend Realtime beyond WebRTC-to-WebRTC communication:
+
+- Ingest audio/video from external sources into WebRTC sessions
+- Stream WebRTC media to external systems for processing or storage
+- Integrate with AI services for transcription, translation, or generation
+- Bridge WebRTC applications with legacy communication systems
+
+## Available adapters
+
+### WebSocket adapter (beta)
+
+Stream audio between WebRTC tracks and WebSocket endpoints. Currently in beta; the API may change.
+
+[Learn more](/realtime/sfu/media-transport-adapters/websocket-adapter/)
+
+## Architecture
+
+Media Transport Adapters operate as intermediaries between Cloudflare Realtime SFU sessions and external endpoints:
+
+```mermaid
+graph LR
+    A[WebRTC Client] <--> B[Realtime SFU Session]
+    B <--> C[Media Transport Adapter]
+    C <--> D[External Endpoint]
+```
+
+### Key concepts
+
+**Adapter instance**: Each connection creates a unique instance with an `adapterId` to manage its lifecycle.
+
+**Location types**:
+- `local` (Ingest): Receives media from external endpoints to create new WebRTC tracks
+- `remote` (Stream): Sends media from existing WebRTC tracks to external endpoints
+
+**Codec support**: Adapters convert between WebRTC and external system formats.
+
+## Common use cases
+
+### AI processing
+
+- Speech-to-text transcription
+- Text-to-speech generation
+- Real-time translation
+- Audio enhancement
+
+### Media recording
+
+- Cloud recording
+- Content delivery networks
+- Media processing pipelines
+
+### Legacy integration
+
+- Traditional telephony
+- Broadcasting infrastructure
+- Custom media servers
+
+## API overview
+
+Media Transport Adapters are managed through the Realtime SFU API:
+
+```
+POST /v1/apps/{appId}/adapters/{adapterType}/new
+POST /v1/apps/{appId}/adapters/{adapterType}/close
+```
+
+Each adapter type has specific configuration requirements and capabilities. Refer to individual adapter documentation for detailed API specifications.
+
+## Best practices
+
+- Close adapter instances when no longer needed
+- Implement reconnection logic for network failures
+- Choose codecs based on bandwidth and quality requirements
+- Secure endpoints with authentication for sensitive media
+
+## Limitations
+
+- Each adapter type has specific codec and format support
+- Network latency between Cloudflare edge and external endpoints affects real-time performance
+- Maximum message size and streaming modes vary by adapter type
+
+## Get started
+
+[WebSocket adapter (beta)](/realtime/sfu/media-transport-adapters/websocket-adapter/) - Stream audio between WebRTC and WebSocket endpoints