How to retrieve TAG information
Many formats add some information, also known as Tags, to the song binary in order to allow an immediate identification of the file contents: the availability of this information and its contents can be retrieved using the following methods:
IsTagAvailable determines if a certain type of tag is contained inside the song binary
Note that, in order to speed up the sound file loading, tag information is not available immediately after the call of the
LoadSound method: once the sound is loaded, you can force the control to read tag information using the
ReadSoundInfo method.
If dealing with playlists, you can use the
PlayListGetItemString method in order to receive a string containing the needed information.
Usually tags are internally implemented as concatenated strings: the only exception is the
ID3V2 tag format used by MP3 songs: this format is far more complex because allows the use of binary data. Specifications about this tag format can be found on the
ID3V2 official web site.
Due to the ID3V2 format complexity, our control will give the possibility to retrieve the full tag binary content but will not give information about the single elements inside the tag; for this purpose we have implemented the following methods:
GetMp3Tag2Data retrieves the full binary contents of the ID3V2 tag for a MP3 sound
Note that the
GetMp3Tag2Data needs to receive from its container a memory buffer that will be filled with the tag binary: the buffer allocation is responsibility of the container which can obtain the buffer size calling the
GetMp3Tag2Size.
Below you can find a couple of samples that demonstrate how to retrieve a ID3V2 tag in Visual Basic 6 and Visual C++ 6:
Visual Basic 6
Private Sub Command1_Click()
Amp3dj1.LoadSound 0, "mysong.mp3"
Amp3dj1.ReadSoundInfo 0
If Amp3dj1.IsTagAvailable(0, TAGTYPE_ID3V2) = 0 Then
Amp3dj1.CloseSound (0)
Exit Sub
End If
Dim ntagSize As Long
ntagSize = Mp3play1.GetMp3Tag2Size(0)
Dim pBuffer() As Byte
ReDim pBuffer(ntagSize)
Amp3dj1.GetMp3Tag2Data 0, pBuffer, ntagSize
...
use of the tag contents
...
End Sub
Visual C++ 6 with MFC
void CReadId3v2Dlg::OnButton1()
{
m_player.LoadSound (0, "mysound.mp3");
m_player.ReadSoundInfo (0);
if (m_player.IsTagAvailable (0, TAGTYPE_ID3V2) == 0)
{
m_player.CloseSound (0);
return;
}
long nTagSize = m_player.GetMp3Tag2Size (0);
if (nTagSize == 0)
{
m_player.CloseSound (0);
return;
}
BYTE *pTagBuffer = new BYTE[nTagSize];
COleVariant var;
var.vt = VT_BYREF | VT_UI1;
var.pbVal = pTagBuffer;
m_player.GetMp3Tag2Data (0, var, nTagSize);
...
use of the tag contents
...
delete pTagBuffer;
}
