# pipe2jpeg
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Parse individual jpegs from an FFmpeg pipe when the output codec(**-c:v**) is set to ***mjpeg*** and the format(**-f**) is set to ***image2pipe***, ***singlejpeg***, ***mjpeg***, or ***mpjpeg***.
### installation:
```
npm install pipe2jpeg --save
```
### usage:
The following example uses ffmpeg's **testsrc** to simulate a video input and generate 100 downscaled jpeg images at a rate of 1 per second. The jpeg images are piped in from ffmpeg's stdout and parsed for the start of image(SOI) and end of image(EOI) file markers. Using the default configuration, Pipe2Jpeg dispatches a "data" event that contains a complete jpeg image buffer. For more configuration options, view the [docs](https://kevingodell.github.io/pipe2jpeg/Pipe2Jpeg.html).
```javascript
const Pipe2Jpeg = require('pipe2jpeg');

const { spawn } = require('child_process');

let jpegCounter = 0;

const params = [
  /* log info to console */
  '-loglevel',
  'quiet',

  /* use an artificial video input */
  '-re',
  '-f',
  'lavfi',
  '-i',
  'testsrc=size=1920x1080:rate=15',

  /* set output flags */
  '-an',
  '-c:v',
  'mjpeg',
  '-pix_fmt',
  'yuvj420p',
  '-f',
  'image2pipe', // image2pipe, singlejpeg, mjpeg, or mpjpeg
  '-vf',
  'fps=1,scale=640:360',
  '-q',
  '2',
  '-frames',
  '100',
  'pipe:1'
];

const p2j = new Pipe2Jpeg();

p2j.on('data', (jpeg) => {
  console.log('received jpeg', ++jpegCounter);
});

const ffmpeg = spawn('ffmpeg', params, {stdio : ['ignore', 'pipe', 'ignore']});

ffmpeg.on('error', (error) => {
  console.log(error);
});

ffmpeg.on('exit', (code, signal) => {
  console.log('exit', code, signal);
});

ffmpeg.stdout.pipe(p2j);
```
Setting **readableObjectMode** to true will cause the output to be an object containing **list** and **totalLength** properties:
```javascript
const p2j = new Pipe2Jpeg({ readableObjectMode: true /* default false */ });

p2j.on('data', ({ list, totalLength }) => {
  // list is array of buffers comprising the jpeg
  console.log(Array.isArray(list), Buffer.isBuffer(list[0]));
  // totalLength is cumulative size of buffers in list
  console.log(Number.isInteger(totalLength));
  // list of buffers can be concatenated as needed
  const jpeg = Buffer.concat(list, totalLength);
});

// the list property will be set with the latest value
const list = p2j.list;
```
While **readableObjectMode** is set to true, **bufferConcat** can be set to true to cause the list of buffers to be concatenated into a single buffer:
```javascript
const p2j = new Pipe2Jpeg({ readableObjectMode: true /* default false */, bufferConcat: true /* default false */ });

p2j.on('data', ({ jpeg }) => {
  // jpeg is complete as a single buffer
  console.log(Buffer.isBuffer(jpeg));
});

// the jpeg property will be set with the latest value
const jpeg = p2j.jpeg;
```
If you have consistently sized jpegs, then setting **byteOffset** to a number approximately 75% of the expected size can minimize the time searching for EOI and result in a small performance gain:
```javascript
const p2j = new Pipe2Jpeg({ byteOffset: 10000 /* default 200 */ });
```
While **readableObjectMode** is set to false or **bufferConcat** is set to true, an experimental buffer pool can be used to reduce garbage collection and increase performance:
```javascript
const p2j = new Pipe2Jpeg({ pool: 1 /* default 0 */ });
```
### testing:
Clone the repository
```
git clone https://github.com/kevinGodell/pipe2jpeg.git
```
Change into the directory
```
cd pipe2jpeg
```
Initialize with npm
```
npm install
```
Start the tests
```
npm test
```