chrome/test/data/webrtc/video_detector.js

   1 /**
   2  * Copyright (c) 2012 The Chromium Authors. All rights reserved.
   3  * Use of this source code is governed by a BSD-style license that can be
   4  * found in the LICENSE file.
   5  */
   6
   7 // This file requires the functions defined in test_functions.js.
   8
   9 var gFingerprints = [];
  10
  11 // Public interface.
  12
  13 /**
  14  * Starts capturing frames from a video tag. The algorithm will fingerprint a
  15  * a frame every now and then. After calling this function and running for a
  16  * while (at least 200 ms) you will be able to call isVideoPlaying to see if
  17  * we detected any video.
  18  *
  19  * @param {string} videoElementId The video element to analyze.
  20  * @param {string} canvasId A canvas element to write fingerprints into.
  21  * @param {int}    width The video element's width.
  22  * @param {int}    width The video element's height.
  23  *
  24  * @return {string} Returns ok-started to the test.
  25  */
  26 //
  27 function startDetection(videoElementId, canvasId, width, height) {
  28   var video = document.getElementById(videoElementId);
  29   var canvas = document.getElementById(canvasId);
  30   var NUM_FINGERPRINTS_TO_SAVE = 5;
  31
  32   setInterval(function() {
  33     var context = canvas.getContext('2d');
  34     captureFrame_(video, context, width, height);
  35     gFingerprints.push(fingerprint_(context, width, height));
  36     if (gFingerprints.length > NUM_FINGERPRINTS_TO_SAVE) {
  37       gFingerprints.shift();
  38     }
  39   }, 100);
  40
  41   returnToTest('ok-started');
  42 }
  43
  44 /**
  45  * Checks if we have detected any video so far.
  46  *
  47  * @return {string} video-playing if we detected video, otherwise
  48  *                  video-not-playing.
  49  */
  50 function isVideoPlaying() {
  51   // Video is considered to be playing if at least one finger print has changed
  52   // since the oldest fingerprint. Even small blips in the pixel data will cause
  53   // this check to pass. We only check for rough equality though to account for
  54   // rounding errors.
  55   try {
  56     if (gFingerprints.length > 1) {
  57       if (!allElementsRoughlyEqualTo_(gFingerprints, gFingerprints[0])) {
  58         returnToTest('video-playing');
  59         return;
  60       }
  61     }
  62   } catch (exception) {
  63     throw failTest('Failed to detect video: ' + exception.message);
  64   }
  65   returnToTest('video-not-playing');
  66 }
  67
  68 // Internals.
  69
  70 /** @private */
  71 function allElementsRoughlyEqualTo_(elements, element_to_compare) {
  72   if (elements.length == 0)
  73     return false;
  74
  75   var PIXEL_DIFF_TOLERANCE = 100;
  76   for (var i = 0; i < elements.length; i++) {
  77     if (Math.abs(elements[i] - element_to_compare) > PIXEL_DIFF_TOLERANCE) {
  78       return false;
  79     }
  80   }
  81   return true;
  82 }
  83
  84 /** @private */
  85 function captureFrame_(video, canvasContext, width, height) {
  86   canvasContext.drawImage(video, 0, 0, width, height);
  87 }
  88
  89 /** @private */
  90 function fingerprint_(canvasContext, width, height) {
  91   var imageData = canvasContext.getImageData(0, 0, width, height);
  92   var pixels = imageData.data;
  93
  94   var fingerprint = 0;
  95   for (var i = 0; i < pixels.length; i++) {
  96     fingerprint += pixels[i];
  97   }
  98   return fingerprint;
  99 }