This interface is exposed by renderers, typically a video renderer, to return information about the performance achieved — for example, the number of frames per second (fps). The values returned through the interface are reset each time the filter is stopped. The base classes of the Microsoft® DirectShow™ Software Development Kit (SDK) have a standard property page that displays the information available from this interface.
When to Implement
The IQualProp interface is implemented by the DirectShow video renderer. Other video renderers might want to implement this interface as well, although it is optional.
When to Use
Applications use this interface to retrieve video renderer performance information.
Methods in Vtable Order
| IUnknown methods | Description |
| QueryInterface | Returns pointers to supported interfaces. |
| AddRef | Increments the reference count. |
| Release | Decrements the reference count. |
| IQualProp methods | Description |
| get_AvgFrameRate | Retrieves the average frame rate achieved. |
| get_AvgSyncOffset | Retrieves the average time difference between when a frame was due for rendering and when rendering actually began (this is returned as a value in milliseconds). |
| get_DevSyncOffset | Retrieves the average time difference between when a frame was due for rendering and when rendering actually began (this is returned as a standard deviation). |
| get_FramesDrawn | Retrieves the number of frames drawn since streaming started. |
| get_FramesDroppedInRenderer | Retrieves the number of frames dropped by the renderer. |
| get_Jitter | Expresses the average time between successive frames delivered to the video renderer. |
Retrieves the average frame rate since streaming started.
HRESULT get_AvgFrameRate(
int *piAvgFrameRate
) PURE;
Returns an HRESULT value.
Retrieves the average time difference between when the video frames should have been displayed and when they actually were.
HRESULT get_AvgSyncOffset(
int *piAvg
);
Returns an HRESULT value.
Retrieves the average time difference between when the video frames should have been displayed and when they actually were. This method is the same as the IQualProp::get_AvgSyncOffset method except that the value returned is calculated as a standard deviation rather than as a simple average.
HRESULT get_DevSyncOffset(
int *piDev
);
Returns an HRESULT value.
When playing video from networks, the presentation can often be disrupted by network glitches. For this reason, expressing the accuracy of video frames by a simple average is inappropriate. Looking at a standard deviation provides a better idea of the overall accuracy.
Retrieves the number of frames drawn since streaming started.
HRESULT get_FramesDrawn(
int *pcFramesDrawn
);
Returns an HRESULT value.
Retrieves the number of frames dropped by the renderer.
HRESULT get_FramesDroppedInRenderer(
int *pcFrames
);
Returns an HRESULT value.
The property page uses this method to retrieve data from the renderer.
Expresses the average time between successive frames delivered to the video renderer.
HRESULT get_Jitter(
int *piJitter
);
Returns an HRESULT value.
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