/// <summary>
/// Construct from file info; parse ID3 tags from stream and calculate where the audio must be
/// </summary>
/// <param name="fileinfo"></param>
public MP3FileData(FileInfo fileinfo)
{
_sourceFileInfo = fileinfo;
// create an empty frame model, to use if we don't parse anything better
TagModel tagModel = new TagModel();
// don't know how big the audio is until we've parsed the tags
UInt32 audioNumBytes;
using( FileStream sourceStream = fileinfo.Open( FileMode.Open, FileAccess.Read, FileShare.Read ) )
{
// all the header calculations use UInt32;
// this guarantees all the file offsets we have to deal with fit in a UInt32
if( sourceStream.Length > UInt32.MaxValue )
throw new InvalidAudioFrameException( "MP3 file can't be bigger than 4gb" );
// in the absence of any recognised tags,
// audio starts at the start
_audioStart = 0;
// audio is entire file length
audioNumBytes = (UInt32)sourceStream.Length;
// try to read an ID3v1 block.
// If ID3v2 block exists, its values overwrite these
// Otherwise, if ID3V1 block exists, its values are used
// The audio is anything that's left after all the tags are excluded.
try
{
ID3v1 id3v1 = new ID3v1();
id3v1.Deserialize( sourceStream );
// fill in ID3v2 block from the ID3v1 data
tagModel = id3v1.FrameModel;
// audio is shorter by the length of the id3v1 tag
audioNumBytes -= ID3v1.TagLength;
}
catch( TagNotFoundException )
{
// ignore "no ID3v1 block"
// everything else isn't caught here, and throws out to the caller
}
try
{
sourceStream.Seek( 0, SeekOrigin.Begin );
tagModel = TagManager.Deserialize( sourceStream );
// audio starts after the tag
_audioStart = (uint)sourceStream.Position;
// audio is shorter by the length of the id3v2 tag
audioNumBytes -= _audioStart;
}
catch( TagNotFoundException )
{
// ignore "no ID3v2 block"
// everything else isn't caught here, and throws out to the caller
}
// create a taghandler to hold the tagmodel we've parsed, if any
_tagHandler = new TagHandler( tagModel );
} // closes sourceStream
// save the location of the audio in the original file
// passing in audio size and id3 length tag (if any) to help with bitrate calculations
_audio = new AudioFile( fileinfo, _audioStart, audioNumBytes, _tagHandler.Length );
_audioReplaced = false;
}
/// <summary>
/// append or overwrite ID3v1 tag at the end of the audio
/// </summary>
/// <param name="stream"></param>
public void WriteID3v1( Stream stream )
{
ID3v1 v1tag = new ID3v1();
v1tag.FrameModel = TagModel;
stream.Seek(_audioStart + _audio.NumPayloadBytes, SeekOrigin.Begin);
v1tag.Write(stream);
}