b38dea0597
Share Gaia assets and adapters, keep private profiles and development documents local, and update both public READMEs.
79 lines
2.1 KiB
JavaScript
79 lines
2.1 KiB
JavaScript
/* 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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