CPosPassThru Class

Article
06/30/2006

This class is a utility class that handles the IMediaPosition and IMediaSeeking interfaces for single-input pin renderers and transform filters.

IMediaPosition is the interface originally used for seeking in time-based media streams. IMediaSeeking is an interface intended to replace IMediaPosition in filter graphs that require seeking to units other than time, such as samples or fields, or that require more precise time-based seeking.

Renderers will use this class to implement IMediaPosition and IMediaSeeking from the filter; transform filters will use it to implement these two interfaces from the output pin. In both cases, the methods will be implemented by calls to the IMediaPosition or IMediaSeeking interface provided by the output pin of the connected upstream filter, effectively passing the position information through to the next filter.

Create a class derived from CPosPassThru, giving it the IPin pointer to your input pin, and delegate all IMediaPosition and IMediaSeeking methods to it. The class will find the output pin connected to the input pin, query this output pin for the IMediaPosition or IMediaSeeking interface, and respond appropriately.

Protected Data Members

Member	Description
m_Pin	Pointer to the input pin of the filter.

Member Functions

Member function	Description
CPosPassThru	Constructs a CPosPassThru object.
ForceRefresh	Releases any cached interfaces held on the upstream pin.

Overrideable Member Functions

Member function	Description
GetMediaTime	Retrieves the starting and ending media times.

Implemented IMediaPosition Methods

Method	Description
CanSeekBackward	Determines if the current position can be moved backward in the media stream.
CanSeekForward	Determines if the current position can be moved forward in the media stream.
get_CurrentPosition	Retrieves the current position in terms of the total length of the media stream.
get_Duration	Retrieves the total duration of the media stream.
get_PrerollTime	Retrieves the time before the start position that the filter graph will start any nonrandom access device rolling.
get_Rate	Retrieves the playback rate, relative to normal playback of the media.
get_StopTime	Retrieves the position within the media at which playback should stop.
put_CurrentPosition	Sets the position within the media at which playback should start.
put_PrerollTime	Sets the time before the start position that the filter graph will start any nonrandom access device rolling.
put_Rate	Sets the playback rate, relative to normal playback of the media.
put_StopTime	Sets the position within the media at which playback should stop.

Implemented IMediaSeeking Methods

Method	Description
CheckCapabilities	Determines which capabilities exist on a media stream by applying seeking capability flags and checking the returned value.
ConvertTimeFormat	Converts a time from one time format to another.
GetAvailable	Returns the range of times in which seeking is efficient.
GetCapabilities	Retrieves the seeking capabilities of the media stream.
GetCurrentPosition	Retrieves the current position within the media stream.
GetDuration	Retrieves the length of time that the media stream will play.
GetPositions	Retrieves the current start and stop position settings.
GetPreroll	Retrieves the preroll settings.
GetRate	Retrieves the current rate.
GetStopPosition	Retrieves the position at which the media stream stops.
GetTimeFormat	Retrieves the current media time format.
IsFormatSupported	Determines if a specified time format is supported.
IsUsingTimeFormat	Determines if the time format being used in the call is the same as the one the interface currently uses.
QueryPreferredFormat	Retrieves the preferred time format the interface will use.
SetPositions	Sets current and stop positions and applies flags to both.
SetRate	Sets a new playback rate.
SetTimeFormat	Sets the time format, which determines the format of units used during seeking.

Implemented INonDelegatingUnknown Methods

Method	Description
NonDelegatingQueryInterface	Returns a specified reference-counted interface.

Requirements

DirectShow applications and DirectShow filters have different include file and link library requirements. See Setting Up the Build Environment for more information.

OS Versions: Windows CE 2.12 and later. Version 2.12 requires DXPAK 1.0 or later.
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Last updated on Wednesday, April 13, 2005

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