1/* 2 * Copyright 2017, The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17const WINSCOPE_META_MAGIC_STRING = [0x23, 0x56, 0x56, 0x31, 0x4e, 0x53, 0x43, 0x30, 0x50, 0x45, 0x54, 0x31, 0x4d, 0x45, 0x21, 0x23]; // #VV1NSC0PET1ME!# 18 19// Suitable only for short patterns 20function findFirstInArray(array, pattern) { 21 for (var i = 0; i < array.length; i++) { 22 var match = true; 23 for (var j = 0; j < pattern.length; j++) { 24 if (array[i + j] != pattern[j]) { 25 match = false; 26 break; 27 } 28 } 29 if (match) { 30 return i; 31 } 32 } 33 return -1; 34} 35 36function parseUintNLE(buffer, position, bytes) { 37 var num = 0; 38 for (var i = bytes - 1; i >= 0; i--) { 39 num = num * 256 40 num += buffer[position + i]; 41 } 42 return num; 43} 44 45function parseUint32LE(buffer, position) { 46 return parseUintNLE(buffer, position, 4) 47} 48 49function parseUint64LE(buffer, position) { 50 return parseUintNLE(buffer, position, 8) 51} 52 53function mp4Decoder(buffer) { 54 var dataStart = findFirstInArray(buffer, WINSCOPE_META_MAGIC_STRING); 55 if (dataStart < 0) { 56 throw new Error('Unable to find sync metadata in the file. Are you using the latest Android ScreenRecorder version?'); 57 } 58 dataStart += WINSCOPE_META_MAGIC_STRING.length; 59 var frameNum = parseUint32LE(buffer, dataStart); 60 dataStart += 4; 61 var timeline = []; 62 for (var i = 0; i < frameNum; i++) { 63 timeline.push(parseUint64LE(buffer, dataStart) * 1000); 64 dataStart += 8; 65 } 66 return [buffer, timeline] 67} 68 69export { mp4Decoder }; 70