vision.labeler.loading.VideoSource Class

Namespace: vision.labeler.loading
Superclasses: vision.labeler.loading.MultiSignalSource

Load signals from video sources into Ground Truth Labeler app

Since R2020a

Description

The vision.labeler.loading.VideoSource class creates an interface for loading signals from video data sources into the Ground Truth Labeler app. In the Add/Remove Signal dialog box of the app, when Source Type is set to Video, this class controls the parameters in that dialog box.

To access this dialog box, in the app, select Import > Add Signals.

The default implementation of this class loads the video formats accepted by the VideoReader object.

The vision.labeler.loading.VideoSource class is a handle class.

Creation

When you export labels from a Ground Truth Labeler app session that contains video sources, the exported groundTruthMultisignal object stores instances of this class in its DataSource property.

To create a VideoSource object programmatically, such as when programmatically creating a groundTruthMultisignal object, use the vision.labeler.loading.VideoSource function (described here).

Syntax

vidSource = vision.labeler.loading.VideoSource

Description

vidSource = vision.labeler.loading.VideoSource creates a VideoSource object for loading signals from video data sources. To specify the data source and the parameters required to load the source, use the loadSource method.

Properties

Name — Name of source type

"Video" (default) | string scalar

Name of the type of source that this class loads, specified as a string scalar.

Attributes:

GetAccess	public
Constant	true
NonCopyable	true

Description — Description of class functionality

"A video reader" (default) | string scalar

Description of the functionality that this class provides, specified as a string scalar.

Attributes:

GetAccess	public
Constant	true
NonCopyable	true

SourceName — Name of data source

[] (default) | string scalar

Name of the data source, specified as a string scalar. Typically, SourceName is the name of the file from which the signal is loaded.

Attributes:

GetAccess	public
SetAccess	protected

SourceParams — Parameters for loading video signal from data source

[] (default) | structure

Parameters for loading a video signal from a data source, specified as a structure.

This table describes the required and optional fields of the SourceParams structure.

Field	Description	Required or Optional
Timestamps	Timestamps for the video signal, specified as a cell array containing a single duration vector of timestamps. In the Add/Remove Signal dialog box of the app, if you set the Timestamps parameter to From Workspace and read the timestamps from a variable in the MATLAB® workspace, then the SourceParams property stores these timestamps in the Timestamps field.	Optional In the Add/Remove Signal dialog box of the app, if you set the Timestamps parameter to From File and read the timestamps from the video file, then the structure does not include this field, and the SourceParams property is empty, [].

Attributes:

GetAccess	public
SetAccess	protected

SignalName — Names of signals in data source

[] (default) | string vector

Names of the signals that can be loaded from the data source, specified as a string vector.

Attributes:

GetAccess	public
SetAccess	protected

SignalType — Types of signals in data source

[] (default) | vector of vision.labeler.loading.SignalType enumerations

Types of the signals that can be loaded from the data source, specified as a vector of vision.labeler.loading.SignalType enumerations. Each signal listed in the SignalName property is of the type in the corresponding position of SignalType.

Attributes:

GetAccess	public
SetAccess	protected

Timestamp — Timestamps of signals in data source

[] (default) | cell array of duration vectors

Timestamps of the signals that can be loaded from the data source, specified as a cell array of duration vectors. Each signal listed in the SignalName property has the timestamps in the corresponding position of Timestamp.

Attributes:

GetAccess	public
SetAccess	protected

NumSignals — Number of signals in data source

0 (default) | integer

Number of signals that can be read from the data source, specified as a nonnegative integer. NumSignals is equal to the number of signals in the SignalName property.

Attributes:

GetAccess	public
SetAccess	public
Dependent	true
NonCopyable	true

Methods

Public Methods

customizeLoadPanel	customizeLoadPanel(sourceObj,panel) Customize the loading panel for the data source object. In the loading dialog box of the app, this method is invoked when you select the data source type from the Source Type list.
getLoadPanelData	[sourceName,sourceParams] = getLoadPanelData(sourceObj) Obtain the data needed to load the data source object currently selected in the loading panel. In the loading dialog box of the app, this method is invoked when you add a source. The method returns these outputs. sourceName is a string capturing the name of the data source object. sourceParams is a structure with fields containing the parameters required to load the data source object. Both of these outputs are passed to the loadSource method.
loadSource	loadSource(sourceObj,sourceName,sourceParams) Load a data source object into the app. In the loading dialog box of the app, this method is invoked after you add a source and the getLoadPanelData method executes successfully. This method is also invoked when you load the data source object into the MATLAB workspace. When you load the data source object, MATLAB expects that the source has the name sourceName and parameters sourceParams that are needed to load that source and read data from it.
readFrame	frame = readFrame(sourceObj,signalName,tsIndex) Read a frame of data from a signal contained in a data source object at the specified timestamp index. The index must be in the bounds of the length of the timestamps for that signal.
loadPanelChecker	loadPanelChecker Check the load panel for the loading dialog box of the app. This method opens a dialog box similar to the loading dialog box that you open from the Open menu on the app toolstrip. Use this method to preview how the customizeLoadPanel method populates the loading panel for the selected data source object. Static true

Examples

Create Video Source

Create a video source from a video on the MATLAB® search path. Load the source name into the VideoSource object. The video has no source parameters needed to load it, so sourceParams is empty.

sourceName = 'caltech_cordova1.avi';
sourceParams = [];

vidSource = vision.labeler.loading.VideoSource;
loadSource(vidSource,sourceName,sourceParams);

Read the first frame from the video. Display the frame.

signalName = vidSource.SignalName;
I = readFrame(vidSource,signalName,1);

figure
imshow(I)

Tips

• You can this class as a starting point for creating a custom data source loading class. To view the source code for this class, use this command:

  edit vision.labeler.loading.VideoSource

Version History

Introduced in R2020a