pva-to-video 0.0.2

HTTP service that provides on demand video streams from NTNDArrays served over EPICS PVA

pva_to_video

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

What	Where
Source	https://github.com/DiamondLightSource/pva-to-video
PyPI	pip install pva-to-video
Docker	docker run ghcr.io/diamondlightsource/pva-to-video:latest
Releases	https://github.com/DiamondLightSource/pva-to-video/releases

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

Flag	Default	Description
--host	0.0.0.0	Bind address
--port	8080	Bind port
--log-level	info	debug, info, warning, or error

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