MP3 Jukebox Assignments

In the assignments in this chapter, we will write, in stages, a program that serves as an MP3 playlist generator and database manager. It will generate and play selections of MP3 songs based on what it can find on our file system and it will permit filter-queries based on data stored in ID3v2 (meta) tag information.

25.1	Data Model: Mp3File	553
25.2	Visitor: Generating Playlists	555
25.3	Preference: An Enumerated Type	556
25.4	Reusing id3lib	559
25.5	PlayListModel Serialization	560
25.6	Testing Mp3File Related Classes	561
25.7	Simple Queries and Filters	561
25.8	Mp3PlayerView	563
25.9	Models and Views: PlayList	565
25.10	Source Selector	566
25.11	Persistent Settings	567
25.12	Edit Form View for FileTagger	568
25.13	Database View	569

The features we will implement are inspired by open-source programs such as amaroK and Juk (and commercial programs such as iTunes and MusicMatch Jukebox). These programs all provide similar features and similar styles of user interface.

The code that does the actual file-tagging is taken from an open-source library, id3lib^[1] version 3.8.3. This is the same library that is used by MusicMatch Jukebox.

^[1] http://sourceforge.net/projects/id3lib

The media player shown in Figure 25.1 has three major components.

1.	A player view that shows the user what is currently playing and provides some controls for changing volume or position of the song
2.	A selector that permits the user to choose (and create new) playlists for manipulating or playback
3.	A song list view, for displaying a list of songs in a tabular form

Figure 25.1. Example screenshot

Each of these major components has a view for displaying the data and a model for storing the data.

• The model for a Mp3PlayerView consists of Mp3Player plus a FileTagger.
• The model for a source selector is a tree, and you can use either QtreeWidgetItem or QAbstractItemModel as the base class for this.
• To start with, the model for a song list view will be a simple PlayList. Later in the chapter, we will implement another model based on QSqlRelationalTableModel.

Figure 25.2 shows a high-level UML diagram of the major components of this project. We can see that the Controller class, derived from QApplication, owns all other objects.

Figure 25.2. The Controller and its managed objects