ID3 is a metadata container most often used in conjunction with the MP3 audio file format. It allows information such as the title, artist, album, track number, and other information about the file to be stored in the file itself.";
this.infoURL = "https://wikipedia.org/wiki/ID3";
this.inputType = "ArrayBuffer";
this.outputType = "JSON";
this.presentType = "html";
this.args = [];
}
/**
* @param {ArrayBuffer} input
* @param {Object[]} args
* @returns {JSON}
*/
run(input, args) {
input = new Uint8Array(input);
/**
* Extracts the ID3 header fields.
*/
function extractHeader() {
if (!Array.from(input.slice(0, 3)).equals([0x49, 0x44, 0x33]))
throw new OperationError("No valid ID3 header.");
const header = {
"Type": "ID3",
// Tag version
"Version": input[3].toString() + "." + input[4].toString(),
// Header version
"Flags": input[5].toString()
};
input = input.slice(6);
return header;
}
/**
* Converts the size fields to a single integer.
*
* @param {number} num
* @returns {string}
*/
function readSize(num) {
let result = 0;
// The sizes are 7 bit numbers stored in 8 bit locations
for (let i = (num) * 7; i; i -= 7) {
result = (result << i) | input[0];
input = input.slice(1);
}
return result;
}
/**
* Reads frame header based on ID.
*
* @param {string} id
* @returns {number}
*/
function readFrame(id) {
const frame = {};
// Size of frame
const size = readSize(4);
frame.Size = size.toString();
frame.Description = FRAME_DESCRIPTIONS[id];
input = input.slice(2);
// Read data from frame
let data = "";
for (let i = 1; i < size; i++)
data += String.fromCharCode(input[i]);
frame.Data = data;
// Move to next Frame
input = input.slice(size);
return [frame, size];
}
const result = extractHeader();
const headerTagSize = readSize(4);
result.Size = headerTagSize.toString();
const tags = {};
let pos = 10;
// While the current element is in the header
while (pos < headerTagSize) {
// Frame Identifier of frame
let id = String.fromCharCode(input[0]) + String.fromCharCode(input[1]) + String.fromCharCode(input[2]);
input = input.slice(3);
// If the next character is non-zero it is an identifier
if (input[0] !== 0) {
id += String.fromCharCode(input[0]);
}
input = input.slice(1);
if (id in FRAME_DESCRIPTIONS) {
const [frame, size] = readFrame(id);
tags[id] = frame;
pos += 10 + size;
} else if (id === "\x00\x00\x00") { // end of header
break;
} else {
throw new OperationError("Unknown Frame Identifier: " + id);
}
}
result.Tags = tags;
return result;
}
/**
* Displays the extracted data in a more accessible format for web apps.
* @param {JSON} data
* @returns {html}
*/
present(data) {
if (!data || !Object.prototype.hasOwnProperty.call(data, "Tags"))
return JSON.stringify(data, null, 4);
let output = `
Tag
Description
Data
`;
for (const tagID in data.Tags) {
const description = data.Tags[tagID].Description,
contents = data.Tags[tagID].Data;
output += `