# Layout

## PC Directory

`PC Directory` is simply a special non-removable container. Any media file added will have an entry inside the PC Directory tree. PC Directory’s hierarchy reflects the file system hierarchy, all objects inside the PC Directory including itself are NON-VIRTUAL objects.

All other entries are virtual objects and may have a different title, description, etc., but they are still referencing to objects in the PC-Directory. That’s why it is not possible to change the phyiscal location property of a virtual object - the only exceptions are URL items.

If an entry is deleted from the PC Directory all its referenes in the virtual structure are deleted as well.

If your virtual layout is the only thing needed, the PC Directory can be hidden completely from browsing.

## Virtual Layout Basics

This section will give you some overview on how virtual objects work.

### Understanding Virtual Objects

When you add a file or directory to the database several things happen.

1. The object is inserted into the `PC Directory`.

2. Once an item is added to the PC Directory it is forwarded to the virtual object engine. The virtual object engine’s mission is to organize and present the media database in a logical hierarchy based on the available metadata of the items.

Each UPnP server implements this so called virtual object hierarchy in a different way. Files are usually sorted by artist, album, some servers may just present a view similar to the file system and so on. In Gerbera we try to allow changing this by a scriptable virtual object engine.

### Theory of Operation

After an item is added to the PC Directory it is automatically fed as input to the layout creation. This creates one or more virtual items for the given original item. Items created from layout are always marked virtual.

When a playlist item is encountered, it is automatically fed as input to the playlist script. The playlist script attempts to parse the playlist and adds new item to the database, the item is then processed by the import script.

Updating items only works in import-mode `grb`.

## Virtual Layout Options

The type of virtual layout can be selection by option virtual-layout.

### Builtin Layout

In order to provide the basic virtual layout you can find elsewhere and for really low key systems. Builtin layout is hardcoded and cannot be changed without a new gerbera version but it also offers some configuration options via Boxlayout Configuration.

### js Layout

To implement more sophisticated layouts and populate additional metadata fields we integrated a javascript runtime engine. For more details see Scripting.

At the moment there are three different layout functions for audio files and one for videos and images. The layout function can be set in configuration of Import Function.

Layout Function | Description | Code
--- | --- | ---
importAudio | Create default audio layout similar to builtin layout | da
importAudioInitial | Create a folder for each album artist. Suitable for large collections | ia
importAudioStructured | Create boxes for a group of initial letters in one box | sa
importVideo | Create video layout similar to builtin layout | dv
importImage | Create image layout similar to builtin layout | di

### Playlists

When a playlist item is encountered, it is automatically fed as input to the playlist function `importPlaylist`. The playlist function attempts to parse the playlist according to its file type and adds new items to the database, which item is then processed by the import script. Changing `size` for boxlayout `Playlist/allDirectories` changes the depth of the hierarchy under the Directories node.

## Layout Configuration

In order to avoid changing scripts or code, layout configuration allow, e.g., setting the captions of entries in the virtual layout tree. Each box allows to disable it by setting the attribute `enabled="false"`. If a parent box is disabled all child boxes will disappear from the layout. Boxes in `AudioStructured` support setting the size which means the number of initials in that box.

The following table lists the settings that are handled by the respective layout. The codes in js layout column refer to the Code column above.

Box | Default Caption | js layout | builtin layout
--- | --- | --- | ---
Audio/allAlbums | Albums | da, ia | yes
Audio/allArtists | Artists | da, ia | yes
Audio/allAudio | All Audio | da, ia | yes
Audio/allComposers | Composers | da, ia | yes
Audio/allDirectories | Directories | da, ia | yes
Audio/allGenres | Genres | da, ia | yes
Audio/allSongs | All Songs | da, ia | yes
Audio/allTracks | All - full name | da, ia | yes
Audio/allYears | Year | da, ia | yes
Audio/audioRoot | Audio | da, ia | yes
Audio/artistChronology | Album Chronology | da, ia | yes
AudioInitial/abc | ABC | ia | no
AudioInitial/allArtistTracks | 000 All | ia | no
AudioInitial/allBooks | Books | ia | no
AudioInitial/audioBookRoot | AudioBooks | ia | no
AudioStructured/allAlbums | -Album- | sa | no
AudioStructured/allArtistTracks | all | sa | no
AudioStructured/allArtists | -Artist- | sa | no
AudioStructured/allGenres | -Genre- | sa | no
AudioStructured/allTracks | -Track- | sa | no
AudioStructured/allYears | -Year- | sa | no
Video/allDates | Date | dv | yes
Video/allDirectories | Directories | dv | yes
Video/allVideo | All Video | dv | yes
Video/allYears | Year | dv | yes
Video/unknown | Unknown | dv | yes
Video/videoRoot | Video | dv | yes
Image/allDates | Date | di | yes
Image/allDirectories | Directories | di | yes
Image/allImages | All Photos | di | yes
Image/allYears | Year | di | yes
Image/imageRoot | Photos | di | yes
Image/unknown | Unknown | di | yes
Trailer/trailerRoot | Online Services | dt | yes
Trailer/allTrailers | All Trailers | dt | yes
Trailer/allGenres | Genres | dt | yes
Trailer/relDate | Release Date | dt | yes
Trailer/postDate | Post Date | dt | yes
Trailer/unknown | Unknown | dt | yes
Playlist/playlistRoot | Playlists | dt | no
Playlist/allPlaylists | All Playlists | dt | no
Playlist/allDirectories | Directories | dt | no

The complete list of configuration options can be found in Boxlayout Configuration.