Created
May 29, 2010 18:40
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/* | |
* Support for iTunes-style m4a tags | |
* See: | |
* http://atomicparsley.sourceforge.net/mpeg-4files.html | |
* http://developer.apple.com/mac/library/documentation/QuickTime/QTFF/Metadata/Metadata.html | |
* Authored by Joshua Kifer <joshua.kifer gmail.com> | |
*/ | |
var ID4 = {}; | |
(function() { | |
ID4.types = { | |
'0' : 'uint8', | |
'1' : 'text', | |
'13' : 'jpeg', | |
'14' : 'png', | |
'21' : 'uint8' | |
}; | |
ID4.atom = { | |
'©alb': ['album'], | |
'©art': ['artist'], | |
'©ART': ['artist'], | |
'aART': ['artist'], | |
'©day': ['year'], | |
'©nam': ['title'], | |
'©gen': ['genre'], | |
'trkn': ['track'], | |
'©wrt': ['composer'], | |
'©too': ['encoder'], | |
'cprt': ['copyright'], | |
'covr': ['picture'], | |
'©grp': ['grouping'], | |
'keyw': ['keyword'], | |
'©lyr': ['lyrics'], | |
'©gen': ['genre'] | |
}; | |
ID4.readID3Range = function(data) { | |
return null; | |
} | |
ID4.readTagsFromData = function(data) { | |
var tag = {}; | |
var seek = 0; | |
readAtom(tag, data, 0, data.getLength()); | |
return tag; | |
}; | |
function readAtom(tag, data, offset, length, indent) | |
{ | |
indent = indent === undefined ? "" : indent + " "; | |
var seek = offset; | |
while (seek < offset + length) | |
{ | |
var atomSize = data.getLongAt(seek, true); | |
if (atomSize == 0) return; | |
var atomName = data.getStringAt(seek + 4, 4); | |
// Container atoms | |
if (['moov', 'udta', 'meta', 'ilst'].indexOf(atomName) > -1) | |
{ | |
if (atomName == 'meta') seek += 4; // next_item_id (uint32) | |
readAtom(tag, data, seek + 8, atomSize - 8, indent); | |
return; | |
} | |
// Value atoms | |
if (ID4.atom[atomName]) | |
{ | |
var klass = data.getInteger24At(seek + 16 + 1, true); | |
var atom = ID4.atom[atomName]; | |
var type = ID4.types[klass]; | |
if (atomName == 'trkn') | |
{ | |
tag[atom[0]] = data.getByteAt(seek + 16 + 11); | |
tag['count'] = data.getByteAt(seek + 16 + 13); | |
} | |
else | |
{ | |
// 16: name + size + "data" + size (4 bytes each) | |
// 4: atom version (1 byte) + atom flags (3 bytes) | |
// 4: NULL (usually locale indicator) | |
var dataStart = seek + 16 + 4 + 4; | |
var dataEnd = atomSize - 16 - 4 - 4; | |
switch( type ) { | |
case 'text': | |
tag[atom[0]] = data.getStringAt(dataStart, dataEnd); | |
break; | |
case 'uint8': | |
tag[atom[0]] = data.getShortAt(dataStart); | |
break; | |
case 'jpeg': | |
case 'png': | |
tag[atom[0]] = { | |
format : "image/" + type, | |
data : data.getBytesAt(dataStart, dataEnd) | |
}; | |
break; | |
} | |
} | |
} | |
seek += atomSize; | |
} | |
} | |
})(); |
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