b38dea0597
Share Gaia assets and adapters, keep private profiles and development documents local, and update both public READMEs.
131 lines
3.7 KiB
JavaScript
Executable file
131 lines
3.7 KiB
JavaScript
Executable file
/* global BlobView */
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/* exported VorbisPictureComment */
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'use strict';
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var VorbisPictureComment = (function() {
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/**
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* Read the picture frame from the block blob
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*/
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function readPicFrame(view) {
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// Source of the structure:
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// https://xiph.org/flac/format.html#metadata_block_picture
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// http://flac.sourceforge.net/format.html#metadata_block_picture
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//
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var kind = view.readUnsignedInt();
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if (kind != 3) {
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return null;
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}
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var mime_len = view.readUnsignedInt();
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var mimetype = view.readLatin1Text(mime_len);
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if (mimetype === '-->') {
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// XXX: We don't support URLs (the spec recommends against them anyway).
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console.error('URL for cover art is not supported.');
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return null;
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}
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// Skip desc, w, h, bpp and indexed colours.
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var desc_len = view.readUnsignedInt();
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view.advance(desc_len + 16);
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var pic_len = view.readUnsignedInt();
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var pic_start = view.sliceOffset + view.viewOffset + view.index;
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// Now return an object that specifies where to pull the image from
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// The properties of this object can be passed to blob.slice()
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return {
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flavor: 'embedded',
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start: pic_start,
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end: pic_start + pic_len,
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type: mimetype
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};
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}
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// BEGIN slow base64
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// https://developer.mozilla.org/en-US/docs/Web/API/WindowBase64/Base64_encoding_and_decoding
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// This is needed as atob doesn't yield the right result.
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function base64DecToArr(sBase64, nBlocksSize) {
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function b64ToUint6(nChr) {
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return nChr > 64 && nChr < 91 ?
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nChr - 65
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: nChr > 96 && nChr < 123 ?
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nChr - 71
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: nChr > 47 && nChr < 58 ?
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nChr + 4
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: nChr === 43 ?
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62
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: nChr === 47 ?
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63
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: 0;
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}
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var sB64Enc = sBase64.replace(/[^A-Za-z0-9\+\/]/g, '');
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var nInLen = sB64Enc.length;
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var nOutLen = nBlocksSize ?
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Math.ceil((nInLen * 3 + 1 >> 2) / nBlocksSize) * nBlocksSize :
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nInLen * 3 + 1 >> 2;
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var taBytes = new Uint8Array(nOutLen);
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for (var nMod3, nMod4, nUint24 = 0, nOutIdx = 0, nInIdx = 0;
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nInIdx < nInLen; nInIdx++) {
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nMod4 = nInIdx & 3;
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nUint24 |= b64ToUint6(sB64Enc.charCodeAt(nInIdx)) << 18 - 6 * nMod4;
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if (nMod4 === 3 || nInLen - nInIdx === 1) {
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for (nMod3 = 0; nMod3 < 3 && nOutIdx < nOutLen; nMod3++, nOutIdx++) {
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taBytes[nOutIdx] = nUint24 >>> (16 >>> nMod3 & 24) & 255;
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}
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nUint24 = 0;
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}
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}
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return taBytes;
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}
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// END
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//
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// Will parse the vorbis comment for picture from metadata.picture.
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// If it doesn't exists, it is a no-op.
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function parsePictureComment(metadata) {
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return new Promise(function(resolve, reject) {
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if (!metadata.picture) {
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resolve(metadata);
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return;
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}
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var value = metadata.picture;
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try {
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// Album art in ogg
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// http://wiki.xiph.org/VorbisComment
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// http://flac.sourceforge.net/format.html#metadata_block_picture
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// Image block is in base64.
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var binary = base64DecToArr(value);
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var aBlob = new Blob([binary]);
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BlobView.get(aBlob, 0, aBlob.size, function(block, err) {
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var prop = readPicFrame(block);
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if (prop) {
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// we need to duplicate the blob because we need
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// to set the MIME type now.
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metadata.picture = {
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flavor: 'unsynced',
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blob: aBlob.slice(prop.start, prop.end, prop.type)
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};
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}
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resolve(metadata);
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}, BlobView.bigEndian);
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}
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catch(e) {
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console.warn('Error parsing picture comment', e.message);
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resolve(metadata);
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}
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});
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}
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return {
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readPicFrame: readPicFrame,
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parsePictureComment: parsePictureComment
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};
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})();
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