pva_to_video

HTTP service that converts EPICS PVA NTNDArray streams into MJPEG video streams consumable by any web browser.

Overview

EPICS areaDetector cameras publish images as NTNDArray structures over PVA. Desktop tools like Phoebus can display these streams directly, but web applications cannot speak PVA. pva-to-video bridges the gap by subscribing to a PVA channel on demand and re-encoding the pixel data as an MJPEG stream served over HTTP — a format every browser understands natively via an <img> tag.

How it works

1. A client requests GET /mjpg/<PV_NAME>.
2. The service opens a PVA monitor on PV_NAME (if one is not already open).
3. Each incoming NTNDArray is normalised to uint8 and JPEG-encoded.
4. Frames are pushed to all connected clients as a multipart/x-mixed-replace MJPEG stream, capped at 30 fps per client.
5. When the last client disconnects the subscription is kept alive for 60 s to avoid churn, then torn down automatically.

Supported pixel formats: uint8/16/32/64, int8/16/32/64, and float32/64. Greyscale (2-D) and colour (H×W×3 RGB) arrays are both handled.

Usage

Embedding in a web page

Point an <img> tag at the service:

<img src="https://my-server:8080/mjpg/BL01T-DI-CAM-01:PVA:OUTPUT" />

A built-in viewer page is available at GET / for quick manual testing.

Running with pip

pip install pva-to-video
pva-to-video                        # listen on 0.0.0.0:8080
pva-to-video --port 9000            # custom port
pva-to-video --log-level debug      # verbose logging

If cameras are on a different subnet, set the PVA name server:

EPICS_PVA_NAME_SERVERS=192.168.1.50 pva-to-video

Running with Docker

docker run --rm -p 8080:8080 ghcr.io/diamondlightsource/pva-to-video:latest

To reach IOCs on the host network:

docker run --rm --network host ghcr.io/diamondlightsource/pva-to-video:latest

With a remote PVA gateway:

docker run --rm -p 8080:8080 \
  -e EPICS_PVA_NAME_SERVERS=192.168.1.50 \
  ghcr.io/diamondlightsource/pva-to-video:latest

CLI options

Trying it with example-services

The epics-containers/example-services repository provides a simulated areaDetector camera (bl01t-di-cam-01) and a PVA gateway (pvagw) that bridges the camera stream to 127.0.0.1:9075.

Follow the epics-containers workstation setup tutorial to install Docker or Podman and clone example-services, then follow the launch a simulation beamline tutorial to start the simulation IOC.

Once the services are running, start pva-to-video:

EPICS_PVA_NAME_SERVERS=127.0.0.1:9075 pva-to-video

Open http://localhost:8080 in a browser, enter the PV name BL01T-DI-CAM-01:PVA:OUTPUT, and click View to see the live 1024 × 1024 simulated detector image. You can also point an <img> tag directly at the stream:

http://localhost:8080/mjpg/BL01T-DI-CAM-01:PVA:OUTPUT