b38dea0597
Share Gaia assets and adapters, keep private profiles and development documents local, and update both public READMEs.
79 lines
2.1 KiB
JavaScript
Executable file
79 lines
2.1 KiB
JavaScript
Executable file
/* global BlobView */
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/* exported ID3v1Metadata */
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'use strict';
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/**
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* Parse files with ID3v1 metadata. Metadata includes title, artist, album,
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* and possibly the track number. Year, comment and genre are ignored.
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*
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* Format information:
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* http://www.id3.org/ID3v1
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* http://en.wikipedia.org/wiki/ID3
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*/
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var ID3v1Metadata = (function() {
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/**
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* Parse a file and return a Promise with the metadata.
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*
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* @param {BlobView} blobview The audio file to parse.
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* @return {Promise} A Promise returning the parsed metadata object.
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*/
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function parse(blobview) {
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return new Promise(function(resolve, reject) {
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var blob = blobview.blob;
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BlobView.get(blob, blob.size - 128, 128, function(footer, error) {
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if (error) {
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reject(error);
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return;
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}
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try {
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var magic = footer.getBinaryText(0, 3);
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if (magic === 'TAG') {
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// It's an MP3 file with an ID3v1 tag.
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resolve(parseID3v1Metadata(footer));
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} else {
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// It's an MP3 file with no metadata. Just resolve to an empty
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// metatada object.
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resolve({});
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}
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} catch (e) {
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reject(e);
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}
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});
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});
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}
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/**
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* Parse ID3v1 metadata from the 128 bytes footer at the end of a file.
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*
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* @param {BlobView} footer The last 128 bytes of the file.
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* @return {Metadata} The parsed metadata object.
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*/
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function parseID3v1Metadata(footer) {
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footer.seek(3); // Skip the "TAG" prefix.
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var title = footer.readNullTerminatedLatin1Text(30, true);
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var artist = footer.readNullTerminatedLatin1Text(30, true);
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var album = footer.readNullTerminatedLatin1Text(30, true);
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footer.advance(32); // Skip year and comment.
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var zerobyte = footer.readUnsignedByte();
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var track = footer.readUnsignedByte();
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var metadata = {
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tag_format: 'id3v1',
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title: title || undefined,
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artist: artist || undefined,
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album: album || undefined
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};
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if (zerobyte === 0 && track !== 0) {
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metadata.tracknum = track;
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}
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return metadata;
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}
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return {
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parse: parse
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};
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})();
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