/**
* Copyright 2012 The Chromium Authors
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
// This file requires the functions defined in test_functions.js.
var gFingerprints = [];
var gDetectorInterval = null;
// Public interface.
/**
* Starts capturing frames from a video tag. The algorithm will fingerprint a
* a frame every now and then. After calling this function and running for a
* while (at least 200 ms) you will be able to call isVideoPlaying to see if
* we detected any video.
*
* @param {string} videoElementId The video element to analyze.
* @param {int} width The video element's width.
* @param {int} width The video element's height.
*
* @return {string} Returns ok-started to the test.
*/
//
function startDetection(videoElementId, width, height) {
var video = document.getElementById(videoElementId);
if (!video)
throw failTest('Could not find video element with id ' + videoElementId);
if (gDetectorInterval)
throw failTest('Detector is already running.');
var NUM_FINGERPRINTS_TO_SAVE = 5;
var canvas = document.createElement('canvas');
canvas.style.display = 'none';
gFingerprints = [];
gDetectorInterval = setInterval(function() {
var context = canvas.getContext('2d', {willReadFrequently: true});
if (video.videoWidth == 0)
return; // The video element isn't playing anything.
captureFrame_(video, context, width, height);
gFingerprints.push(fingerprint_(context, width, height));
if (gFingerprints.length > NUM_FINGERPRINTS_TO_SAVE) {
gFingerprints.shift();
}
}, 100);
return logAndReturn('ok-started');
}
/**
* Checks if we have detected any video so far.
*
* @return {string} video-playing if we detected video, otherwise
* video-not-playing.
*/
function isVideoPlaying() {
// Video is considered to be playing if at least one finger print has changed
// since the oldest fingerprint. Even small blips in the pixel data will cause
// this check to pass. We only check for rough equality though to account for
// rounding errors.
try {
if (gFingerprints.length > 1) {
if (!allElementsRoughlyEqualTo_(gFingerprints, gFingerprints[0])) {
clearInterval(gDetectorInterval);
gDetectorInterval = null;
return 'video-playing';
}
}
} catch (exception) {
throw failTest('Failed to detect video: ' + exception.message);
}
return 'video-not-playing';
}
/**
* Checks if the video has stopped
*
* @return {string} video-stopped or video-not-stopped.
*/
function isVideoStopped() {
// Video is considered to be stopped if the last 5 fingerprints are the same.
// We only check for rough equality though to account for rounding errors.
if (gFingerprints.length < 5) {
return 'video-not-stopped';
}
if (allElementsRoughlyEqualTo_(gFingerprints.slice(-5),
gFingerprints[gFingerprints.length - 1])) {
return 'video-stopped';
}
return 'video-not-stopped';
}
/**
* Queries for the stream size (not necessarily the size at which the video tag
* is rendered).
*
* @param videoElementId The video element to check.
* @return {string} ok-<width>x<height>, e.g. ok-640x480 for VGA.
*/
function getStreamSize(videoElementId) {
var video = document.getElementById(videoElementId);
if (!video)
throw failTest('Could not find video element with id ' + videoElementId);
return logAndReturn('ok-' + video.videoWidth + 'x' + video.videoHeight);
}
// Internals.
/** @private */
function allElementsRoughlyEqualTo_(elements, element_to_compare) {
if (elements.length == 0)
return false;
var PIXEL_DIFF_TOLERANCE = 100;
for (var i = 0; i < elements.length; i++) {
if (Math.abs(elements[i] - element_to_compare) > PIXEL_DIFF_TOLERANCE) {
return false;
}
}
return true;
}
/** @private */
function captureFrame_(video, canvasContext, width, height) {
canvasContext.drawImage(video, 0, 0, width, height);
}
/** @private */
function fingerprint_(canvasContext, width, height) {
var imageData = canvasContext.getImageData(0, 0, width, height);
var pixels = imageData.data;
var fingerprint = 0;
for (var i = 0; i < pixels.length; i++) {
fingerprint += pixels[i];
}
return fingerprint;
}
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