Reading ID3 tags from a WMA file (MP3 as well)

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Introduction

I wanted to get to the ID3 taqs (artist, album, title, genre, ...) in a WMA file, and found out that it's not quite as straightforward as it is getting the ID3V1.1 tags from an MP3 file. So I created a set of classes, one to get the ID3V1.1 tags from an MP3 file (easy), and another to get the same information out of a WMA file.

Background

You can find the ASF specification here: Advanced Systems Format (ASF) Specification. It is the internal file format of a WMA file.

Using the code

The classes are fairly straightforward to use. You simply create an instance of either WMAID3Tag or ID3V1Tag, specifying the filename of the music file, and then you can access the key information directly:

//
// Allocate a WMAID3Tag and access the fields
//
Try
    w = New WMAID3Tag(tbFilename.Text)
Catch ex As Exception
    MsgBox(tbFilename.Text & " is not a valid wma" & _ 
           " file or has invalid tag information")
    Return
End Try

tbTitle.Text = w.title
tbArtist.Text = w.artist
tbAlbum.Text = w.album
tbGenre.Text = w.genre
tbYear.Text = w.year.ToString
tbTrack.Text = w.track.ToString
tbDescription.Text = w.description

Points of Interest

One interesting side note is that the .NET classes that read/write Unicode strings (like BinaryReader/Writer or StreamReader/Writer) use an interesting convention for the length field at the start of the string. It appears that strings less than 255 characters use a single byte for the length, but others use two bytes. It's not clear (to me) exactly how this works, but since in the WMA files the length field is always two bytes, you can't use the .NET routines.