The IAMExtDevice interface is the base interface for controlling external devices. Developers can implement this interface to control numerous types of devices; however, the current DirectShow implementation is specific to VCRs. The IAMExtDevice interface controls general settings of external hardware and is intended to be used in combination with the IAMExtTransport interface, which controls a VCR's more specific settings. You can also implement the IAMTimecodeReader, IAMTimecodeGenerator, and IAMTimecodeDisplay interfaces if your filter manages SMPTE (Society of Motion Picture and Television Engineers) timecode, and the external device has the appropriate features.
For a description of a sample filter which controls a VCR through DirectShow, see VCR Device Control Filter.
When to Implement
Implement this interface when you want to build a filter or application that controls an external device, such as a VCR. Because this interface controls general information about a device, implement the IAMExtTransport interface in addition to control the external device's more specific properties.
An application can directly instantiate and control external devices, such as VCRs, but it is strongly recommended that you always instantiate these devices within the context of a filter graph, even if they are the only filters within the graph.
When to Use
Use this interface when you want to add external device control to your application.
Applications should use the filter graph to enumerate the filters and then get the IAMExtDevice interface directly from the appropriate filter.
Hardware Requirements
To control an external VCR, certain hardware requirements are recommended. VCRs with an RS-422 serial interface require a special serial port card or an external RS-232-to-RS-422 adapter. In addition, for best performance, your computer should have a serial port card built with a 16,550 high-performance UART (Universal Asynchronous Receiver/Transmitter) to sustain higher baud rates, such as 38.4 baud.
Methods in Vtable Order
| IUnknown Methods | Description |
| QueryInterface | Retrieves pointers to supported interfaces. |
| AddRef | Increments the reference count. |
| Release | Decrements the reference count. |
| IAMExtDevice Methods | Description |
| GetCapability | Retrieves the capabilities of the external device. |
| get_ExternalDeviceID | Retrieves the model number of the external device. |
| get_ExternalDeviceVersion | Retrieves the version number of the external device's operating software. |
| put_DevicePort | Specifies the communication port to which the external device is connected. |
| get_DevicePower | Retrieves whether the external device's power mode is on, off, or standby. |
| put_DevicePower | Sets the external device's power mode to on, off, or standby. |
| Calibrate | Calibrates the external device's transport mechanism. |
| get_DevicePort | Retrieves the communication port to which the external device is connected. |
Calibrates an external device's transport mechanism.
HRESULT Calibrate(
HEVENT hEvent,
long Mode,
long *pStatus );
| Value | Meaning |
| ED_ACTIVE | Activates calibration process. |
| ED_INACTIVE | Deactivates calibration process. |
| NULL | Used to determine if current status is active or inactive. |
Returns an HRESULT value that depends on the implementation of the interface.
Use this method on certain external devices that require calibration; for example, when rewinding a tape and resetting the counter, or computing the frame offset for a timecode reader or generator.
Filters for various external devices can implement this method differently, depending on the calibration that the device needs. This method assumes the IMediaEventSink interface has already established an event sink, or that another event signaling method has been established.
Retrieves the communication port to which the external device is connected.
HRESULT get_DevicePort(
long *pDevicePort );
| Value | Meaning |
| DEV_PORT_1394 | IEEE 1394 Bus |
| DEV_PORT_ARTI | ARTI driver |
| DEV_PORT_COM1 | COM1 |
| DEV_PORT_COM2 | COM2 |
| DEV_PORT_COM3 | COM3 |
| DEV_PORT_COM4 | COM4 |
| DEV_PORT_DIAQ | Diaquest driver |
| DEV_PORT_SIM | Simulation port |
| DEV_PORT_USB | Universal Serial Bus |
Returns an HRESULT value that depends on the implementation of the interface.
Retrieves the external device's power mode: on, off, or standby.
HRESULT get_DevicePower(
long *pPowerMode );
| Value | Meaning |
| ED_POWER_OFF | Off |
| ED_POWER_ON | On |
| ED_POWER_STANDBY | Standby |
Returns an HRESULT value that depends on the implementation of the interface.
Retrieves the model number of the external device.
HRESULT get_ExternalDeviceID(
LPOLESTR *ppszData );
Returns an HRESULT value that depends on the implementation of the interface.
Retrieves the version number of the external device's operating software.
HRESULT get_ExternalDeviceVersion(
LPOLESTR *ppszData );
Returns an HRESULT value that depends on the implementation of the interface.
Retrieves the capabilities of the external device.
HRESULT GetCapability(
long Capability,
long *pValue,
double *pdblValue );
| Value | Meaning |
| ED_DEVCAP_CAN_RECORD | Checks whether transport can record. |
| ED_DEVCAP_CAN_RECORD_STROBE | Checks whether transport can single-frame record. |
| ED_DEVCAP_CAN_SAVE | Checks whether transport can save data. |
| ED_DEVCAP_DEVICE_TYPE | Checks the external device type. |
| ED_DEVCAP_HAS_AUDIO | Checks whether transport has audio. |
| ED_DEVCAP_HAS_VIDEO | Checks whether the device has video. |
| ED_DEVCAP_USES_FILES | Checks whether transport has a built-in file system. |
| Value | Meaning |
| ED_DEVTYPE_ATR | Audio Tape Recorder |
| ED_DEVTYPE_CG | Character Generator |
| ED_DEVTYPE_DDR | Digital Disc Recorder |
| ED_DEVTYPE_DVE | Digital video effects unit |
| ED_DEVTYPE_GPI | General purpose interface trigger |
| ED_DEVTYPE_KEYER | Video keyer |
| ED_DEVTYPE_LASERDISK | Laser disc |
| ED_DEVTYPE_MIXER_AUDIO | Audio mixer |
| ED_DEVTYPE_MIXER_VIDEO | Video mixer |
| ED_DEVTYPE_ROUTER | Video router |
| ED_DEVTYPE_TBC | Timebase corrector |
| ED_DEVTYPE_TCG | Timecode generator/reader |
| ED_DEVTYPE_VCR | VCR |
| ED_DEVTYPE_WIPEGEN | Video wipe generator |
| ED_DEVTYPE_JOYSTICK | Joystick |
| ED_DEVTYPE_KEYBOARD | Keyboard |
Returns an HRESULT value that depends on the implementation of the interface.
All return values are in pValue unless you have large or floating point values to return, in which case they are returned in the pdblValue parameter.
Specifies the communication port to which the external device is connected.
HRESULT put_DevicePort(
long DevicePort
);
| Value | Meaning |
| DEV_PORT_1394 | IEEE 1394 Bus |
| DEV_PORT_ARTI | ARTI driver |
| DEV_PORT_COM1 | COM1 |
| DEV_PORT_COM2 | COM2 |
| DEV_PORT_COM3 | COM3 |
| DEV_PORT_COM4 | COM4 |
| DEV_PORT_DIAQ | Diaquest driver |
| DEV_PORT_MIN | DEV_PORT_SIM |
| DEV_PORT_SIM | Simulation port (used for "no hardware" simulation) |
| DEV_PORT_USB | Universal serial bus |
Returns an HRESULT value that depends on the implementation of the interface.
Sets the external device's power mode to either on, off, or standby.
HRESULT put_DevicePower(
long PowerMode );
| Value | Meaning |
| ED_POWER_OFF | Off |
| ED_POWER_ON | On |
| ED_POWER_STANDBY | Standby |
Returns an HRESULT value that depends on the implementation of the interface.
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