IMFMediaSession::Start method (mfidl.h)

Starts the Media Session.


  [in] const GUID        *pguidTimeFormat,
  [in] const PROPVARIANT *pvarStartPosition


[in] pguidTimeFormat

Pointer to a GUID that specifies the time format for the pvarStartPosition parameter. This parameter can be NULL. The value NULL is equivalent to passing in GUID_NULL.

The following time format GUIDs are defined:

Value Meaning
Presentation time. The pvarStartPosition parameter must have one of the following PROPVARIANT types.
  • VT_I8: The pvarStartPosition parameter contains the starting position in 100-nanosecond units, relative to the start of the presentation.
  • VT_EMPTY: Playback starts from the current position.
All media sources support this time format.
Segment offset. This time format is supported by the Sequencer Source. The starting time is an offset within a segment.

Call the MFCreateSequencerSegmentOffset function to create the PROPVARIANT value for the pvarStartPosition parameter.

Note  Requires Windows 7 or later.
Skip to a playlist entry. The pvarStartPosition parameter specifies the index of the playlist entry, relative to the current entry. For example, the value 2 skips forward two entries. To skip backward, pass a negative value. The PROPVARIANT type is VT_I4.

If a media source supports this time format, the IMFMediaSource::GetCharacteristics method returns one or both of the following flags:


[in] pvarStartPosition

Pointer to a PROPVARIANT that specifies the starting position for playback. The meaning and data type of this parameter are indicated by the pguidTimeFormat parameter.

Return value

The method returns an HRESULT. Possible values include, but are not limited to, those in the following table.

Return code Description
The method succeeded.
The operation cannot be performed in the Media Session's current state.
The Media Session has been shut down.


When this method is called, the Media Session starts the presentation clock and begins to process media samples.

This method is asynchronous. When the method completes, the Media Session sends an MESessionStarted event.


Minimum supported client Windows Vista [desktop apps only]
Minimum supported server Windows Server 2008 [desktop apps only]
Target Platform Windows
Header mfidl.h
Library Mfuuid.lib

See also