v4l2-camera-ts

Camera library for Linux (V4L2) written in pure TypeScript using libv4l2-ts for the interaction with the kernel.

Installation

npm install v4l2-camera-ts

Usage

import { Camera } from "v4l2-camera-ts";
import fsp from "fs/promises";

async function main() {
	const cam = new Camera();

	cam.open("/dev/video0");

	console.log(cam.queryFormat());

	// the format can only be set before starting
	cam.setFormat({ width: 1920, height: 1080, pixelFormatStr: "MJPG" });
	
	// allocate memory-mapped buffers and turn the stream on
	cam.start();

	// capture 10 frames and write them to JPEG files
	for (let i = 0; i < 10; i++) {
		// asynchronously wait until the camera fd is readable
		// and then exchange one of the memory-mapped buffers
		const frame = await cam.getNextFrame();

		await fsp.writeFile(`./test/frame-${i}.jpg`, frame);
	}

	// turn the stream off and unmap all buffers
	cam.stop();

	cam.close();
}

main();

Methods & Classes

Camera

open(path: string): void
Opens the camera at the specified path.

close(): void
Closes the camera. This needs to be the last operation done on the camera, otherwise its going to throw an error about the device being busy.

queryFormat(): GetCameraFormat
Fetches information about the currently set format from the camera. You can use this to determine if your setFormat call was successful.

setFormat(format: SetCameraFormat): void
Set the width, height, pixel format and optionally the fps of the camera. The fps can only be set for some pixel formats however (not for MJPG for example).

queryControls(): CameraControl[]
Returns a list of all controls on the camera as well as all menu entries for menu controls.

getControl(id: number): number
Get the current value for a control. Valid numbers for the id parameter can be found in v4l2_controls in libv4l2-ts. The constants always begin with V4L2_CID_.

setControl(id: number, value: number): number
Sets a control value. Valid numbers for the id parameter can be found in v4l2_controls in libv4l2-ts. The constants always begin with V4L2_CID_. The function returns the value that was provided in the value parameter.

start(bufferCount: number = 2): void
Create and memory map buffers which are used for data exchange and turn the video stream on. After this call returns, video frames can be retrieved with getNextFrame().

stop(): void
Stops the stream and unmaps all buffers. After this call, buffers returned from getNextFrame() should not be accessed anymore, so make sure to copy all the data out of them before stopping the stream.

async getNextFrame(): Promise<Buffer>
Wait for the next frame to be available, exchange a buffer with the driver and then return that buffer. The buffer will contain data in the format set by setFormat. The returned buffers are not normal Buffers however, since their underlying data points to a memory-mapped region that the V4L2 driver can write into. This means that you need to copy the data out of them (e.g. with Buffer.from(buf)), or they are going to get overwritten by a later call to getNextFrame().