Device dependent properties
Explanations about device-dependent properties.
Most of the video capture device properties are device-dependent.
This means that their content changes when the current video capture device changes.
For this reason these properties are not published, because setting a value from the Object Inspector does allow to specify the concerned video device (selected by the VideoDevice property).
TVideoGrabber saves and retrieves these values for each capture device in the registry in HKEY_CURRENT_USER, under the key. if the "Datastead" key is destroyed it will be recreated automatically and the device settings will be reset to their default values.
The content of these properties is refreshed when the OnVideoDeviceSelected event occurs after selecting the video capture device by assigning a new value to VideoDevice .
The principle is the same for the audio device (OnAudioDeviceSelected and AudioDevice ).
E.g., we have 2 video capture devices on our platform.
- the 1st video device has 3 inputs: "Tuner", "Composite" and "SVideo",
- the 2nd device has 2 composite inputs: "Composite 0" and "Composite 1".
a) on the first video capture device (VideoDevice = 0), the VideoInputs string list returns the following values: "Tuner", "Composite", "SVideo"
The index value VideoInput = 1 means that the Composite video input has been selected on this video capture device.
b) on the 2nd video capture device (VideoDevice = 1), the VideoInputs string list returns the following values: "Composite 0", "Composite 1".
Now the index value VideoInput = 1 means that the "Composite 1" input has been selected on this video capture device.
Moreover, a VideoInput = 2 value that means "SVideo" on the 1st device has no meaning and is out of range on the 2nd device.
Thus, the edit fields, listboxes and indexes of any application using TVideoGrabber MUST be refreshed when the OnVideoDeviceSelected or OnAudioDeviceSelected event occurs, otherwise their content will no longer reflect the current values of the TVideoGrabber properties.
We find mainly 2 types of properties:
- single values
- list / index based values, that can be easily identified as they are composed of a string list, an index in the list, and a list count. e.g.: VideoInput, VideoInputs and VideoInputsCount.
The main device-dependent properties related to the video capture device are:
The main device-dependent properties related to the audio capture device are: