videoproc

This is a small helper module that allows you to substitute a video element with a canvas element. This can be useful when you want to do pixel manipulation of the rendered images, or in situations when a video element does not behave as you expect.

Example Usage

var crel = require('crel');
var videoproc = require('videoproc');
var video = crel('video', { src: '../test/assets/tennis.webm', autoplay: true });
var canvas = crel('canvas');
var processor = videoproc(video, canvas, {
  filter: require('rtc-filter-grayscale')
});
 
document.body.appendChild(canvas);
 

Using the Processing Pipeline

A processing pipeline has been included to assist with manipulating the canvas on the fly. To specify the filters to be used in the processing pipeline, this is done in the options accepted by videoproc. Either specifying an array of filters with the filters option or a single filter function with the filter option is fine. If you use both then the individual filter will be added filter list and used in series.

videoproc(srcVideo, targetCanvas, {
  filters: [
    require('rtc-filter-grayscale'),
    myCustomFilterFunction
  ]
});

Writing a Filter Function

Writing a filter function is very simple, and they use the following function signature:

function filter(imageData, tick) {
}

The imageData arg is an ImageData, and the tick argument refers to the tick that has been captured as part of the capture loop (be aware that it could be a high resolution timer value if rAF is being used).

If you are writing an analysis filter, then simply do what you need to do and exit the function. If you have written a filter that modifies the pixel data and you want this drawn back to the canvas then your filter must return true to tell rtc-videoproc that it should draw the imageData back to the canvas.

Listening for custom frame events

In addition to providing the opportunity to analyse and modify pixel data the rtc-videoproc module also provides the a custom frame event for detecting when a new frame has been drawn to the canvas.

A simple example can be found below:

var videoproc = require('videoproc');
var crel = require('crel');
var video = crel('video', { src: '../test/assets/tennis.webm', autoplay: true });
 
// set up the video processing pipeline
videoproc(video).on('frame', function(tick) {
  console.log('captured frame at: ' + tick);
});
 
// add the canvas to the dom
document.body.appendChild(video);
 

NOTE: The frame event occurs after the filter pipeline has been run and and the imageData may have been modified from the original video frame.

A Note with Regards to CPU Usage

By default rtc-videoproc will draw at 25fps but this can be modified to capture at a lower frame rate for slower devices, or increased if you have a machine with plenty of grunt.

Reference

videoproc(src, target, opts?)

Create (or patch) a <canvas> element that will receive the video images from a video element. The following options are supported.

• canvas - the canvas to draw video data to. If not supplied a new canvas element will be created.

• video - the video element that will be used as the source of the video. If not supplied a new <video> element will be created.

• fps - the redraw rate of the fake video (default = 25)

• greedy - Specify greedy: true if you want the videoproc module to run it's capture loop using setTimeout rather than requestAnimationFrame. Doing this will mean you application will continue to capture and process frames even when it's tab / window becomes inactive. This is usually the desired behaviour with video conferencing applications.

License(s)

ISC

Copyright (c) 2015, Damon Oehlman damon.oehlman@gmail.com

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.