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Example: RTSP Streaming with CustomWriter#

This walkthrough demonstrates how to use the CustomWriter to stream live RTSP video from IRA cameras. The RTSPStreamWriter provided by the isaacsim.streaming.rtsp extension serves as the target writer. This page covers only the minimal working example; for full details on encoding modes, frame metadata, server lifecycle, and troubleshooting, refer to Live Camera Streaming over RTSP.

RTSPStreamWriter streams LdrColor frames over RTSP and supports two encoding modes:

  • hardware-accelerated H.264 (default)

  • raw CUDA

Because it is designed with a one-to-one mapping between writer instances and cameras, each camera requires its own CustomWriter entry with a unique port.

Prerequisites#

  • Isaac Sim is installed and can launch successfully.

  • The isaacsim.replicator.agent.core and isaacsim.replicator.agent.ui extensions are enabled (Enable extensions).

  • An RTSP client is available for playback (for example, VLC, ffplay, or a GStreamer pipeline).

Step 1: Enable the RTSP Streaming Extension#

RTSPStreamWriter is provided by the isaacsim.streaming.rtsp extension. If the extension is not already active, enable it before proceeding:

  1. Open Window > Extensions to launch the Extension Manager.

  2. Search for isaacsim.streaming.rtsp.

  3. If the extension is not enabled, click the toggle to enable it. Check the autoload checkbox if you want it to load automatically on future launches.

After enabled, RTSPStreamWriter registers itself in omni.replicator.core.WriterRegistry and becomes available to the CustomWriter selection dialog.

Step 2: Add a CustomWriter and Select the Writer#

  1. Open the Actor SDG panel (Tools > Action and Event Data Generation > Actor SDG).

  2. Scroll to the Replicator section and click Add Writer.

  3. Select CustomWriter from the writer type list and click Next.

  4. In the Configure CustomWriter dialog, open the Writer Name dropdown and look for RTSPStreamWriter.

    • If RTSPStreamWriter appears in the list, select it, click OK to confirm, and proceed to step 4.

    • If it does not appear, follow step 3 below to register it manually.

Important

Always click OK to confirm after selecting or registering a writer. The CustomWriter is not added until you confirm the dialog.

Step 3: Manual Registration#

If RTSPStreamWriter is not listed in the Writer Name dropdown, the extension may not have been enabled or its self-registration may not have run yet. You can register the writer class manually using the Writer Scope field, which accepts three input modes:

  • A dotted class path to a single writer class.

  • A package or module path to scan for all Writer subclasses.

  • A filesystem path to a .py file containing writer classes.

The system auto-detects the mode. To register RTSPStreamWriter:

  1. In the Writer Scope field, enter the class path:

    isaacsim.streaming.rtsp.impl.rtsp_writer.RTSPStreamWriter

    Alternatively, enter the package path isaacsim.streaming.rtsp to discover all writers in the extension.

  2. Click Register. The system imports the class (or scans the package), validates that each discovered class is a subclass of omni.replicator.core.Writer, and registers it in the WriterRegistry.

  3. The Writer Name dropdown refreshes and RTSPStreamWriter appears. Select it.

  4. Click OK to confirm.

Step 4: Configure the Sensor Prim List#

RTSPStreamWriter is designed with a one-to-one mapping: each writer instance streams from exactly one camera. You must specify the target camera by adding it to the Sensor Prim List within the CustomWriter panel:

  1. In the CustomWriter parameters panel, click Add Parameter and select sensor_prim_list.

  2. Add the prim path of the camera you want to stream (for example, /World/Cameras/Camera_01).

Note

If sensor_prim_list is left empty, the writer attempts to attach to all cameras under the sensor root, which is not supported by RTSPStreamWriter. Always specify exactly one camera per CustomWriter instance.

Step 5: Set the Port and Mount Path#

Each RTSP stream requires a unique network port. When streaming from multiple cameras, assign a different port value to each CustomWriter instance to avoid conflicts.

  1. Click Add Parameter and select port. Set a port number (default is 8554). Valid range is 1–65535.

  2. Click Add Parameter and select mountPath. Enter a descriptive mount path that starts with / (for example, /camera_01). This makes it easier to identify each stream when monitoring.

The resulting RTSP URL for this stream is:

rtsp://localhost:<port><mountPath>

For example, with port: 8554 and mountPath: /camera_01, the stream URL is rtsp://localhost:8554/camera_01.

Step 6: Optional Encoding Settings#

RTSPStreamWriter supports two encoding modes controlled by the encoding parameter:

  • "h264" (default): Pre-encoded H.264 with per-frame SEI metadata injection. This is the recommended mode for most use cases.

  • "raw": Uncompressed CUDA RGBA buffer path. The RTSP backend handles encoding internally.

When using "h264" encoding, you can also configure width and height (default 1920x1080) to set the RTSP server resolution.

Note

The width and height parameters on RTSPStreamWriter do not change the RenderProduct resolution — they only configure the RTSP stream to match the existing input dimensions. To change the actual rendered resolution, first adjust the RenderProduct Resolution in the CustomWriter UI panel, then set the writer’s width and height to match. Mismatched values result in stretched or cropped frames.

Parameter Naming in the UI#

The CustomWriter UI generates its parameter fields automatically from the __init__ signature of the selected writer class (for example, sensorSetName in RTSPStreamWriter). Because you can import custom or third-party writers, no specific parameter naming format is enforced. The UI capitalizes the first letter of each parameter name purely for visual consistency (for example, sensorSetName appears as SensorSetName in the panel), but the underlying value is passed to the writer using its original name.

Multi-camera YAML Example#

The following config streams from two cameras on separate ports. Each CustomWriter instance must use a unique port to avoid conflicts:

replicator:
  writers:
    CustomWriter:
      writer_name: "RTSPStreamWriter"
      writer_scope: "isaacsim.streaming.rtsp"
      sensor_prim_list:
        - "<your_camera_prim_path>"
      port: <your_unique_port>
      mountPath: "<your_mount_path>"
      encoding: "h264"
    CustomWriter_1:
      writer_name: "RTSPStreamWriter"
      writer_scope: "isaacsim.streaming.rtsp"
      sensor_prim_list:
        - "<your_camera_prim_path>"
      port: <your_unique_port>  # Must differ from the port above
      mountPath: "<your_mount_path>"
      encoding: "h264"

Tip

If the isaacsim.streaming.rtsp extension is enabled and RTSPStreamWriter is already registered, writer_scope can be omitted. It is included here for robustness so the config works even when the extension has not been loaded yet. You can also use a full class path (for example, "isaacsim.streaming.rtsp.impl.rtsp_writer.RTSPStreamWriter") instead of a package path if you prefer to register only one specific writer.

Verify the Stream#

After clicking Start Data Generation, open an RTSP client and connect to the stream URL. For example, with ffplay:

ffplay rtsp://localhost:8554/camera_01

You should receive live rendered frames from the corresponding camera. Repeat for each port and mount-path pair to verify all streams.

See also

Live Camera Streaming over RTSP for a full reference for the RTSP streaming pipeline, including encoding modes, frame metadata, server lifecycle, and troubleshooting.