mirror of https://bitbucket.org/ausocean/av.git
63 lines
2.0 KiB
JavaScript
63 lines
2.0 KiB
JavaScript
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/*
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NAME
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lex-mjpeg.js
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AUTHOR
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Trek Hopton <trek@ausocean.org>
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LICENSE
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This file is Copyright (C) 2019 the Australian Ocean Lab (AusOcean)
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It is free software: you can redistribute it and/or modify them
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under the terms of the GNU General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.
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It is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License in gpl.txt.
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If not, see [GNU licenses](http://www.gnu.org/licenses).
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*/
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// MJPEGLexer lexes a byte array containing MJPEG into individual JPEGs.
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class MJPEGLexer{
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constructor(src){
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this.src = src;
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this.off = 0;
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}
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// read returns the next single frame.
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read(){
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// Check if the src can contain at least the start and end flags (4B).
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if(this.off+4 > this.src.length){
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return null;
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}
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// Iterate through bytes until the start flag is found.
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while(this.src[this.off] != 0xff || this.src[this.off+1] != 0xd8){
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this.off++;
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if(this.off+4 > this.src.length){
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return null;
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}
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}
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// Start after the start flag and loop until the end flag is found.
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let end = this.off+2;
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while(true){
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if(end+2 > this.src.length){
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return null;
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}
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if(this.src[end] == 0xff && this.src[end+1] == 0xd9){
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break;
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}
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end++;
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}
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// Copy the frame's bytes to a new array to return.
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// Note: optimally this would return a reference but since we are in a worker thread,
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// the main thread doesn't have access to the ArrayBuffer that we are working with.
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let frame = this.src.slice(this.off, end+2);
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this.off = end+2
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return frame;
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}
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}
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