public static id3tag read_id3tag(System.IO.Stream strm, bool createImageObject)
{
id3tag tag = new id3tag();
byte[] id3_header = new byte[10];// ID3タグヘッダ用
strm.ReadOrThrow(id3_header, 0, 10);
id3v2header header = read_header(id3_header);
if (header == null)
{
return(null);
}
if (header.size >= strm.Length)
{
return(null);
}
tag.head = header;
if ((tag.head.flag & FLAG_HEAD_EXTENSION) > 0)// 拡張ヘッダがあるときサイズだけ読んでスキップ
{
byte[] ext_header = new byte[4];
strm.Read(ext_header, 0, 4);
int size;
if (tag.head.version == 3) // v2.3
{
size = ((ext_header[0] * 256 + ext_header[1]) * 256 + ext_header[2]) * 256 + ext_header[3];
}
else // v2.4
{
size = ((ext_header[0] * 128 + ext_header[1]) * 128 + ext_header[2]) * 128 + ext_header[3] - 4;
}
strm.Seek(size, System.IO.SeekOrigin.Current);
}
/* frame */
byte[] frame_buf = new byte[tag.head.size];
strm.Read(frame_buf, 0, tag.head.size);
if (((tag.head.flag & FLAG_HEAD_UNSYNC) > 0) && tag.head.version == 3)
{
frame_buf = DecodeUnsync(frame_buf);
}
MemoryStream tagBodyStream = new MemoryStream(frame_buf, 0, frame_buf.Length);
int count = 0;
while (true)
{ //offset < tag.head.size
frame fr = read_frame(tagBodyStream, tag, createImageObject);
if (fr == null)
{
break;
}
count++;
tag.frame.Add(fr);
}
return(tag);
}
public static id3v2header read_header(byte[] headerstr)
{
id3v2header header = new id3v2header();
if (Encoding.ASCII.GetString(headerstr, 0, 3) != "ID3")
{
return(null);
}
switch ((headerstr[3] << 8) + headerstr[4])
{
case 0x0200:
header.version = 2;
if ((headerstr[5] & 0x40) > 0)
{
return(null);
}
header.flag = headerstr[5] & 0x80;
break;
case 0x0300:
header.version = 3;
header.flag = headerstr[5] & (0x80 + 0x40 + 0x20);
break;
case 0x0301:
;
goto case 0x0400;
case 0x0400:
header.version = 4;
header.flag = headerstr[5] & (0x80 + 0x40 + 0x20 + 0x10);
break;
default:
return(null);
}
header.size = (headerstr[6] << 21) + (headerstr[7] << 14) + (headerstr[8] << 7) + headerstr[9];
return(header);
}
