doubleTwist | Developers

What

doubleTwist has the ability to customize the way in which it interacts with devices. With the exception of the Sony PSP, most of the knowledge about a device is declared in an external XML file. These external XML files contain "device declarations" and allow customization of device identification, the folder to which music is synced, folders to search for media when browsing a device, decoder capabilities, and encoder settings.

A "catch-all" device declaration exists to provide base support for any device that isn't explicitly identified and customized by other device declarations. It defines the following behavior:

The entire file system (of the largest storage card) is searched for media when browsing the device in doubleTwist.
mp3 files can by synced to the device without incurring a transcode (bitrate: 20 - 320 kb/s, 1 or 2 channels).
Files that require transcoding will be encoded to mp3 at 128 kb/s, 2 channels.

Note that not all interaction with a device is customizable. Most notably, playlists are implemented by writing an M3U file to the root of the file system of the device, which is something that cannot be changed.

Why

Gains in browsing / sync efficiency and in audio quality can be achieved by creating custom device declarations. For example, rather than searching a device's entire file system for media when browsing, a set of sub-folders can be specified to limit the search. When syncing music to a device, if the device is known to support formats other than mp3, alternative decoders can be specified to avoid unnecessary transcoding. Lastly, alternative encode settings can be specified to transcode media into a format better suited for a particular device.

Where

Device declaration files live in a folder called "Devices" under the install folder of the application, which is typically C:\Program Files\doubleTwist. Any file under the Devices folder that has an extension of ".xml" will be treated as a device declaration file and parsed when the application launches, which allows for device declarations to be made across multiple XML files. If there are user-generated device declarations that conflict with doubleTwist's declarations for a given device then the user-generated ones will take precedence.

How

Identifying a device

Specifying the music sync folder

Specifying additional browse folders

Specifying decoder capabilities

Specifying encoder parameters

Overriding doubleTwist device declarations

Reference

Value types

XML structure

Example

<?xml version="1.0" encoding="utf-8" ?>
<Devices>
	<Device>
		<Name>Acme</Name>
		<Identifiers>
			<Identifier>
				<Manufacturer>.*[aA][cC][mM][eE].*</Manufacturer>
				<Model>.*[pP][hH][oO][nN][eE].*</Model>
			</Identifier>
			<Identifier>
				<DeviceID>USB%5C%5CVID_0401%26PID_04AF</DeviceID>
			</Identifier>
		</Identifiers>
		<BrowseFolders>
			<Folder>/Sounds</Folder>
			<Folder>/Video</Folder>
			<Folder>/Images</Folder>
		</BrowseFolders>
		<MusicFolder>/Music</MusicFolder>
		<Decoders>
			<Decoder>
				<Audio>
					<Encoding>mp3</Encoding>
					<Bitrate>20000:320000</Bitrate>
					<Channels>1,2</Channels>
				</Audio>
			</Decoder>
			<Decoder>
				<Audio>
					<Encoding>aac</Encoding>
					<Bitrate>16000:576000</Bitrate>
					<SampleRate>8000:48000</SampleRate>
					<Channels>1,2</Channels>
				</Audio>
			</Decoder>
		</Decoders>
		<AudioEncodeProfile>
			<EncodeProfile>
				<FileFormat>mpg</FileFormat>
				<Audio>
					<Encoding>mp3</Encoding>
					<Bitrate>128000</Bitrate>
					<Channels>2</Channels>
				</Audio>
			</EncodeProfile>
		</AudioEncodeProfile>
	</Device>
</Devices>

Source Code

The source code for some of the doubleTwist components is available as Open Source. Click here to download the source code.

Adding support for a new device

Source Code