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 var gDetectorInterval = null;
  11
  12 // Public interface.
  13
  14 /**
  15  * Starts capturing frames from a video tag. The algorithm will fingerprint a
  16  * a frame every now and then. After calling this function and running for a
  17  * while (at least 200 ms) you will be able to call isVideoPlaying to see if
  18  * we detected any video.
  19  *
  20  * @param {string} videoElementId The video element to analyze.
  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, width, height) {
  28   var video = document.getElementById(videoElementId);
  29   if (!video)
  30     throw failTest('Could not find video element with id ' + videoElementId);
  31
  32   if (gDetectorInterval)
  33     throw failTest('Detector is already running.');
  34
  35   var NUM_FINGERPRINTS_TO_SAVE = 5;
  36   var canvas = document.createElement('canvas');
  37   canvas.style.display = 'none';
  38
  39   gFingerprints = [];
  40   gDetectorInterval = setInterval(function() {
  41     var context = canvas.getContext('2d');
  42     if (video.videoWidth == 0)
  43       return;  // The video element isn't playing anything.
  44
  45     captureFrame_(video, context, width, height);
  46     gFingerprints.push(fingerprint_(context, width, height));
  47     if (gFingerprints.length > NUM_FINGERPRINTS_TO_SAVE) {
  48       gFingerprints.shift();
  49     }
  50   }, 100);
  51
  52   returnToTest('ok-started');
  53 }
  54
  55 /**
  56  * Checks if we have detected any video so far.
  57  *
  58  * @return {string} video-playing if we detected video, otherwise
  59  *                  video-not-playing.
  60  */
  61 function isVideoPlaying() {
  62   // Video is considered to be playing if at least one finger print has changed
  63   // since the oldest fingerprint. Even small blips in the pixel data will cause
  64   // this check to pass. We only check for rough equality though to account for
  65   // rounding errors.
  66   try {
  67     if (gFingerprints.length > 1) {
  68       if (!allElementsRoughlyEqualTo_(gFingerprints, gFingerprints[0])) {
  69         clearInterval(gDetectorInterval);
  70         gDetectorInterval = null;
  71         returnToTest('video-playing');
  72         return;
  73       }
  74     }
  75   } catch (exception) {
  76     throw failTest('Failed to detect video: ' + exception.message);
  77   }
  78   returnToTest('video-not-playing');
  79 }
  80
  81 /**
  82  * Queries for the stream size (not necessarily the size at which the video tag
  83  * is rendered).
  84  *
  85  * @param videoElementId The video element to check.
  86  * @return {string} ok-<width>x<height>, e.g. ok-640x480 for VGA.
  87  */
  88 function getStreamSize(videoElementId) {
  89   var video = document.getElementById(videoElementId);
  90   if (!video)
  91     throw failTest('Could not find video element with id ' + videoElementId);
  92
  93   returnToTest('ok-' + video.videoWidth + 'x' + video.videoHeight);
  94 }
  95
  96 // Internals.
  97
  98 /** @private */
  99 function allElementsRoughlyEqualTo_(elements, element_to_compare) {
 100   if (elements.length == 0)
 101     return false;
 102
 103   var PIXEL_DIFF_TOLERANCE = 100;
 104   for (var i = 0; i < elements.length; i++) {
 105     if (Math.abs(elements[i] - element_to_compare) > PIXEL_DIFF_TOLERANCE) {
 106       return false;
 107     }
 108   }
 109   return true;
 110 }
 111
 112 /** @private */
 113 function captureFrame_(video, canvasContext, width, height) {
 114   canvasContext.drawImage(video, 0, 0, width, height);
 115 }
 116
 117 /** @private */
 118 function fingerprint_(canvasContext, width, height) {
 119   var imageData = canvasContext.getImageData(0, 0, width, height);
 120   var pixels = imageData.data;
 121
 122   var fingerprint = 0;
 123   for (var i = 0; i < pixels.length; i++) {
 124     fingerprint += pixels[i];
 125   }
 126   return fingerprint;
 127 }