mjpeg-decoder

mjpeg-decoder

A NodeJS M-JPEG decoder which can be used to retrieve individual JPEG frames or take a snapshot from a IP/network camera which serves M-JPEG video stream.

Installation

npm install mjpeg-decoder

or

yarn add mjpeg-decoder

Usage

Typically, you use the mjpeg-decoder to read JPEG frames from an M-JPEG video stream.

const fs = require('fs');
const MjpegDecoder = require('mjpeg-decoder');

// create a decoder which delivers a JPEG frame
// via the 'frame' event every 3 seconds.
const decoder = new MjpegDecoder(
  '<your stream url>', { interval: 3000 }
  );

decoder.on('frame', (frame, seq) => {
  fs.writeFileSync(`${seq}.jpg`, frame);
});

decoder.start();

But sometimes, you just want to take a snapshot of the M-JPEG video stream, and then forget. In this case, you can do like this:

// create a decoder which takes a snapshot and forget
const decoder = new MjpegDecoder(
  '<your stream url>', { maxFrames: 1 }
  );
const frame = await decoder.takeSnapshot();
fs.writeFileSync('snapshot.jpg', frame);

Or, you can use the MjpegDecoder.decoderForSnapshot shorthand method to create the decoder instance:

const decoder = MjpegDecoder.decoderForSnapshot('<your stream url>');
const frame = await decoder.takeSnapshot();
fs.writeFileSync('snapshot.jpg', frame);

API

Options

MjpegDecoder.MjpegDecoderOptions

• interval: Specify the time interval in which the frames will be delivered (default: 0)
• maxFrames: Specify the max frames to consume before stopping (default: 0)
• timeout: Specify the timeout before the http connection is aborted (default: 10000ms)

Constructor

constructor(url: string, options?: Partial<MjpegDecoder.MjpegDecoderOptions>)

• url: url of the M-JPEG video stream source.
• options: control how the decoder will work as expected.

How to find the url of the camera? The camera user manual should usually mention the URL, or searching the camera model number should get you a result as well. You can also try this tool http://skjm.com/icam/mjpeg.php or this tool https://www.ispyconnect.com/man.aspx.

decoderForSnapshot

static decoderForSnapshot(
  url: string,
  options?: Partial<MjpegDecoder.MjpegDecoderOptions>
): MjpegDecoder

Create an instance of MjpegDecoder used to take a onetime snapshot of the video stream.

• url: url of the M-JPEG video stream source.
• options: control how the decoder will work as expected.

start

start(): void

Start the M-JPEG decoder and begin consuming the M-JPEG video stream. Listen for 'frame' event to get the decoded JPEG frames sequently.

stop

stop(): void

Stop consuming the M-JPEG video stream.

takeSnapshot

takeSnapshot(): Promise<Buffer>

Take snapshot of the M-JPEG video stream.

Events

frame

on(event: 'frame', listener: (frame: Buffer, seq: number) => void): this

Add listener for frame event which is emitted when a JPEG frame is decoded. The event listener takes the decoded JPEG frame and sequence number as the parameters.

abort

on(event: 'abort', listener: (reason: MjpegDecoder.AbortReason, error?: Error) => void): this

Add listener for abort event which is emitted for some reason. The decoder will stop consuming the video stream in the following cases:

• timeout: network timeout while connecting to the video stream source at the given url.
• http_error: when a network error or http error occured
• invalid_mjpeg_stream: if the source is not a valid M-JPEG video stream
• end: when you call the stop method of the decoder or the max frames have been delivered.
• max_buffer_size_exceeded: when the internal data buffer size reached the limit, and this might be caused by the M-JPEG decoding problem. If you accountered this error, please create an issue.

Capture M-JPEG snapshot the other ways

Use wget:

$ wget <url> -O snapshot.jpg

Use ffmpeg:

ffmpeg -f MJPEG -y -i <url> -r 1 -vframes 1 -q:v 1 snapshot.jpg

References

• https://aeroquartet.com/movierepair/jpeg.en.html
• https://www.media.mit.edu/pia/Research/deepview/exif.html
• https://github.com/jacksonliam/mjpg-streamer/
• https://channel9.msdn.com/coding4fun/articles/MJPEG-Decoder
• https://medium.com/@petehouston/capture-mjpg-streamer-snapshot-9d0e253b9bbd