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Support files with id3v2 tags #4

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14a7316
Support files with id3v2 tags
alza-bitz Apr 28, 2019
0a16505
Additional assert in test for id3v2_offset
alza-bitz May 2, 2019
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1 change: 1 addition & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,7 @@ Once you parse a header, these are the properties you can access from the packag
| -------------------------- | -------- | ------------ | --------- |
| `parsed` | Boolean | Both | `true` |
| `is_valid` | Boolean | Both | `true` |
| `id3v2_offset` | Integer | Both | `42005` |
| `mpeg_version` | Integer | Both | `2` |
| `mpeg_layer` | Integer | Both | `3` |
| `mpeg_has_padding` | Boolean | Both | `true` |
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48 changes: 36 additions & 12 deletions fixtures/file_metadata.js
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,8 @@ module.exports = [
xing_offset: 21,
xing_frames: 223,
xing_bytes: 43008,
num_samples: 576
num_samples: 576,
id3v2_offset: 0
},{
filename: "mp3-cbr-stereo-32000khz-64kbps.mp3",
type: "cbr",
Expand All @@ -20,7 +21,8 @@ module.exports = [
xing_offset: 36,
xing_frames: 146,
xing_bytes: 42336,
num_samples: 1152
num_samples: 1152,
id3v2_offset: 0
},{
filename: "mp3-cbr-mono-44100khz-64kbps.mp3",
type: "cbr",
Expand All @@ -31,7 +33,8 @@ module.exports = [
xing_offset: 21,
xing_frames: 222,
xing_bytes: 46601,
num_samples: 1152
num_samples: 1152,
id3v2_offset: 0
},{
filename: "mp3-cbr-mono-44100khz-128kbps.mp3",
type: "cbr",
Expand All @@ -42,7 +45,8 @@ module.exports = [
xing_offset: 21,
xing_frames: 238,
xing_bytes: 99891,
num_samples: 1152
num_samples: 1152,
id3v2_offset: 0
},{
filename: "mp3-cbr-stereo-44100khz-128kbps.mp3",
type: "cbr",
Expand All @@ -53,7 +57,8 @@ module.exports = [
xing_offset: 36,
xing_frames: 243,
xing_bytes: 101981,
num_samples: 1152
num_samples: 1152,
id3v2_offset: 0
},{
filename: "mp3-cbr-stereo-44100khz-192kbps.mp3",
type: "cbr",
Expand All @@ -64,7 +69,20 @@ module.exports = [
xing_offset: 36,
xing_frames: 247,
xing_bytes: 155479,
num_samples: 1152
num_samples: 1152,
id3v2_offset: 0
},{
filename: "mp3-cbr-stereo-44100khz-192kbps-id3v2.mp3",
type: "cbr",
channels: 2,
samplerate: 44100,
bitrate: 192,
frame_length: 626,
xing_offset: 42041,
xing_frames: 247,
xing_bytes: 155479,
num_samples: 1152,
id3v2_offset: 42005
},{
filename: "mp3-cbr-mono-48000khz-64kbps.mp3",
type: "cbr",
Expand All @@ -75,7 +93,8 @@ module.exports = [
xing_offset: 21,
xing_frames: 215,
xing_bytes: 41472,
num_samples: 1152
num_samples: 1152,
id3v2_offset: 0
},{
filename: "mp3-cbr-stereo-48000khz-128kbps.mp3",
type: "cbr",
Expand All @@ -86,7 +105,8 @@ module.exports = [
xing_offset: 36,
xing_frames: 237,
xing_bytes: 91392,
num_samples: 1152
num_samples: 1152,
id3v2_offset: 0
},{
filename: "mp3-vbr-mono-22050khz-64kbps.mp3",
type: "vbr",
Expand All @@ -97,7 +117,8 @@ module.exports = [
xing_offset: 13,
xing_frames: 205,
xing_bytes: 22813,
num_samples: 576
num_samples: 576,
id3v2_offset: 0
},{
filename: "mp3-vbr-stereo-22050khz-64kbps.mp3",
type: "vbr",
Expand All @@ -108,7 +129,8 @@ module.exports = [
xing_offset: 21,
xing_frames: 215,
xing_bytes: 50342,
num_samples: 576
num_samples: 576,
id3v2_offset: 0
},{
filename: "mp3-vbr-mono-44100khz-128kbps.mp3",
type: "vbr",
Expand All @@ -119,7 +141,8 @@ module.exports = [
xing_offset: 21,
xing_frames: 235,
xing_bytes: 98295,
num_samples: 1152
num_samples: 1152,
id3v2_offset: 0
},{
filename: "mp3-vbr-stereo-44100khz-128kbps.mp3",
type: "vbr",
Expand All @@ -130,6 +153,7 @@ module.exports = [
xing_offset: 36,
xing_frames: 241,
xing_bytes: 77751,
num_samples: 1152
num_samples: 1152,
id3v2_offset: 0
}
];
Binary file added fixtures/mp3-cbr-stereo-44100khz-192kbps-id3v2.mp3
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41 changes: 39 additions & 2 deletions src/Mp3Header.js
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Expand Up @@ -35,6 +35,24 @@ const SAMPLES_PER_FRAME = {
2: {0: 0, 1: 384, 2: 1152, 3: 576}
}

// https://en.wikipedia.org/wiki/Synchsafe
function _unsynchsafe(int) {
var out = 0, mask = 0x7F000000;
while (mask) {
out >>= 1;
out |= int & mask;
mask >>= 8;
}
return out;
}

function _isKthBitSet(n, k) {
if (n & (1 << (k - 1))) {
return true;
}
return false;
}

module.exports = class Mp3Header {

constructor(buffer) {
Expand All @@ -43,6 +61,7 @@ module.exports = class Mp3Header {
this.parsed = false;
this.header = null;
this.is_valid = false;
this.id3v2_offset = 0;

this._parse();
}
Expand All @@ -53,15 +72,33 @@ module.exports = class Mp3Header {
return;
}

// Not enough data to check for id3v2
if (this.buffer.length < 3) {
return;
}

// http://fileformats.archiveteam.org/wiki/ID3#How_to_skip_past_an_ID3v2_segment
var maybe_id3 = this.buffer.toString("ascii", 0, 3);
if (maybe_id3 == "ID3") {
// Decode bytes 6-9 as a 32-bit "synchsafe int" (refer to any ID3v2 spec).
var synchsafe = this.buffer.readInt32BE(6);
var synchsafe_decoded = _unsynchsafe(synchsafe);
this.id3v2_offset = 10 + synchsafe_decoded;
// If the 0x10 bit of byte 5 is set, let OFFSET = OFFSET + 10 (for the footer).
if (_isKthBitSet(this.buffer.readUInt8(5), 2)) {
this.id3v2_offset += 10;
}
}

// Not enough data to read the header
if (this.buffer.length < 4) {
if (this.buffer.length < this.id3v2_offset + 4) {
return;
}

this.parsed = true;

// Read the first 4 bytes
var header = [this.buffer.readUInt8(0), this.buffer.readUInt8(1), this.buffer.readUInt8(2), this.buffer.readUInt8(3)];
var header = [this.buffer.readUInt8(this.id3v2_offset + 0), this.buffer.readUInt8(this.id3v2_offset + 1), this.buffer.readUInt8(this.id3v2_offset + 2), this.buffer.readUInt8(this.id3v2_offset + 3)];
this.is_valid = this._isMpegHeader(header);
if (!this.is_valid) {
return;
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7 changes: 4 additions & 3 deletions src/Mp3Header_spec.js
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Expand Up @@ -6,6 +6,7 @@ describe("MP3Header Parsing", function() {
const fixtures_path = "/../fixtures";
const expected_data = require(`./${fixtures_path}/file_metadata`);
const MAX_FRAME_LENGTH = 2881; // Theoretical max mp3 frame length
const NUMBER_OF_BYTES = 65536 + MAX_FRAME_LENGTH; // Include 64k bytes for id3v2 header

for (const data of expected_data) {

Expand All @@ -20,10 +21,10 @@ describe("MP3Header Parsing", function() {
return;
}

var buffer = new Buffer(MAX_FRAME_LENGTH);
var buffer = new Buffer(NUMBER_OF_BYTES);
var offset = 0;

fs.read(fd, buffer, 0, MAX_FRAME_LENGTH, offset, function(err, bytesRead, buffer) {
fs.read(fd, buffer, 0, NUMBER_OF_BYTES, offset, function(err, bytesRead, buffer) {

if (err) {
return fs.close(fd, function() {
Expand All @@ -46,7 +47,7 @@ describe("MP3Header Parsing", function() {
expect(header.mpeg_has_padding).toBeFalsy();
expect(header.mpeg_num_samples).toBe(data.num_samples);
expect(header.mpeg_bitrate).toBe(data.bitrate*1000);

expect(header.id3v2_offset).toBe(data.id3v2_offset);
fs.close(fd, function() {
done();
});
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2 changes: 1 addition & 1 deletion src/XingHeader.js
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Expand Up @@ -46,7 +46,7 @@ module.exports = class XingHeader {
this.is_valid = false;

// If this header don't contains a Xing/Info tag, nothing to do
this.xing_offset = this.mp3.header.length + XING_OFFSETS[this.mp3.mpeg_version][this.mp3.mpeg_channels];
this.xing_offset = this.mp3.id3v2_offset + this.mp3.header.length + XING_OFFSETS[this.mp3.mpeg_version][this.mp3.mpeg_channels];
this.xing_keyword = this.mp3.buffer.toString("ascii", this.xing_offset, this.xing_offset + 4);
if (this.xing_keyword !== "Xing" && this.xing_keyword != "Info") {
return;
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5 changes: 3 additions & 2 deletions src/XingHeader_spec.js
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Expand Up @@ -6,6 +6,7 @@ describe("XingHeader Parsing", function() {
const fixtures_path = "/../fixtures";
const expected_data = require(`./${fixtures_path}/file_metadata`);
const MAX_FRAME_LENGTH = 2881; // Theoretical max mp3 frame length
const NUMBER_OF_BYTES = 65536 + MAX_FRAME_LENGTH; // Include 64k bytes for id3v2 header

for (const data of expected_data) {

Expand All @@ -22,10 +23,10 @@ describe("XingHeader Parsing", function() {
return;
}

var buffer = new Buffer(MAX_FRAME_LENGTH);
var buffer = new Buffer(NUMBER_OF_BYTES);
var offset = 0;

fs.read(fd, buffer, 0, MAX_FRAME_LENGTH, offset, function(err, bytesRead, buffer) {
fs.read(fd, buffer, 0, NUMBER_OF_BYTES, offset, function(err, bytesRead, buffer) {

if (err) {
return fs.close(fd, function() {
Expand Down