MFFrameRateToAverageTimePerFrame function (mfapi.h)
Converts a video frame rate into a frame duration.
Syntax
HRESULT MFFrameRateToAverageTimePerFrame(
[in] UINT32 unNumerator,
[in] UINT32 unDenominator,
[out] UINT64 *punAverageTimePerFrame
);
Parameters
[in] unNumerator
The numerator of the frame rate.
[in] unDenominator
The denominator of the frame rate.
[out] punAverageTimePerFrame
Receives the average duration of a video frame, in 100-nanosecond units.
Return value
If this function succeeds, it returns S_OK. Otherwise, it returns an HRESULT error code.
Remarks
This function is useful for calculating time stamps on a sample, given the frame rate.
Also, average time per frame is used in the older VIDEOINFOHEADER and VIDEOINFOHEADER2 format structures. This function provides a standard conversion so that all components in the pipeline can use consistent values, if they need to translate between the older format structures and the media type attributes used in Media Foundation.
For certain common frame rates, the function gets the frame duration from a look-up table:
| Frames per second (floating point) | Frames per second (fractional) | Average time per frame |
|---|---|---|
| 59.94 | 60000/1001 | 166833 |
| 29.97 | 30000/1001 | 333667 |
| 23.976 | 24000/1001 | 417188 |
| 60 | 60/1 | 166667 |
| 30 | 30/1 | 333333 |
| 50 | 50/1 | 200000 |
| 25 | 25/1 | 400000 |
| 24 | 24/1 | 416667 |
Most video content uses one of the frame rates listed here. For other frame rates, the function calculates the duration.
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client | Windows Vista [desktop apps only] |
| Minimum supported server | Windows Server 2008 [desktop apps only] |
| Target Platform | Windows |
| Header | mfapi.h |
| Library | Mfplat.lib |
| DLL | Mfplat.dll |