CPosPassThru Class

The CPosPassThru 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

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

Member Functions

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

Overridable Member Functions

Name	Description
GetMediaTime	Retrieves the starting and ending media times.

Implemented IMediaPosition Methods

Name	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

Name	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

Name	Description
NonDelegatingQueryInterface	Returns a specified reference-counted interface.

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CPosPassThru::CanSeekBackward

CPosPassThru Class

Determines if the current position can be moved backward in the media stream.

HRESULT CanSeekBackward(
  LONG *pCanSeekBackward
  );

Parameters

pCanSeekBackward

Set to OATRUE if able to seek backward; otherwise set to OAFALSE.

Return Values

Returns the HRESULT value returned from calling IMediaPosition::CanSeekBackward on the connected pin.

Remarks

This member function calls IMediaPosition::CanSeekBackward on the connected pin and returns the result.

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CPosPassThru::CanSeekForward

CPosPassThru Class

Determines if the current position can be moved forward in the media stream.

HRESULT CanSeekForward(
  LONG *pCanSeekForward
  );

Parameters

pCanSeekForward

Set to OATRUE if able to seek forward; otherwise set to OAFALSE.

Return Values

Returns the HRESULT value returned from calling IMediaPosition::CanSeekForward on the connected pin.

Remarks

This member function calls IMediaPosition::CanSeekForward on the upstream output pin connected to the peer input pin and returns the result.

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CPosPassThru::CheckCapabilities

CPosPassThru Class

Determines which capabilities exist on a media stream by applying seeking capability flags and checking the returned value.

HRESULT CheckCapabilities(
  DWORD * pCapabilities
  );

Parameters

pCapabilities

Pointer to an AM_SEEKING_SEEKING_CAPABILITIES enumerator containing the seeking capabilities flags to apply. These flags can be any combination of the following:

AM_SEEKING_CanGetCurrentPos

AM_SEEKING_CanGetDuration

AM_SEEKING_CanGetStopPos

AM_SEEKING_CanPlayBackwards

AM_SEEKING_CanSeekAbsolute

AM_SEEKING_CanSeekBackwards

AM_SEEKING_CanSeekForwards

Return Values

Returns S_OK if all capabilities in pCapabilities are present, S_FALSE if some are present, or E_FAIL if none are present.

Remarks

This member function implements IMediaSeeking::CheckCapabilities, by calling the IMediaSeeking::CheckCapabilities method on the upstream output pin connected to the peer input pin. The pin that performs the seek operation will return whether the flags presented in the pCapabilities parameter are present. This returned value will then, in turn, propagate to calls made from CPosPassThru::CheckCapabilities member functions in intervening filters.

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CPosPassThru::ConvertTimeFormat

CPosPassThru Class

Converts a time from one format to another.

HRESULT ConvertTimeFormat(
  LONGLONG * pTarget,
  const GUID * pTargetFormat,
  LONGLONG Source,
  const GUID * pSourceFormat
  );

Parameters

pTarget

Time in converted format.

pTargetFormat

GUID of the format to convert to, or the currently selected format if NULL.

Source

Time in original format.

pSourceFormat

GUID of the format to be converted from, or the currently selected format if NULL.

Return Values

Returns the HRESULT value returned from calling IMediaSeeking::ConvertTimeFormat on the connected pin.

Remarks

This member function implements the IMediaSeeking::ConvertTimeFormat method by calling this same method on the upstream filter's output pin.

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CPosPassThru::CPosPassThru

CPosPassThru Class

Constructs a CPosPassThru object.

CPosPassThru(
  const TCHAR *pName,
  LPUNKNOWN pUnk,
  HRESULT * phr,
  IPin * pPin
  );

Parameters

pName

Name of the object used in the CPosPassThru constructor for debugging purposes.

pUnk

Pointer to the owner of this object.

phr

Pointer to an HRESULT value for resulting information.

pPin

Pointer to the input pin for the filter.

Return Values

No return value.

Remarks

Allocate the pName parameter in static memory. This name appears on the debugging terminal upon creation and deletion of the object.

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CPosPassThru::ForceRefresh

CPosPassThru Class

Releases any cached interfaces on the upstream pin.

HRESULT ForceRefresh( );

Return Values

Returns S_OK.

Remarks

For efficiency, the CPosPassThru class can cache the IMediaPosition interface of the connected upstream output pin. This method releases any cached interface pointers and forces them to be obtained again via QueryInterface if needed.

Presently, this class does not cache the upstream IMediaPosition so this member function is not necessary. It is left in for future flexibility.

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CPosPassThru::GetAvailable

CPosPassThru Class

Returns the range of times in which seeking is efficient.

HRESULT GetAvailable(
  LONGLONG * pEarliest,
  LONGLONG * pLatest
  );

Parameters

pEarliest

Earliest time that can be efficiently seeked to.

pLatest

Latest time that can be efficiently seeked to.

Return Values

Return Values

Returns the HRESULT value returned from calling IMediaSeeking::GetAvailable on the connected pin.

Remarks

This member function implements the IMediaSeeking::GetAvailable method by calling this same method on the upstream filter's output pin.

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CPosPassThru::GetCapabilities

CPosPassThru Class

Returns the seeking capabilities of the media stream.

HRESULT GetCapabilities(
  DWORD * pCapabilities
  );

Parameters

pCapabilities

Seeking capability flags, which can be any combination of the following.

AM_SEEKING_CanGetCurrentPos

AM_SEEKING_CanGetDuration

AM_SEEKING_CanGetStopPos

AM_SEEKING_CanPlayBackwards

AM_SEEKING_CanSeekAbsolute

AM_SEEKING_CanSeekBackwards

AM_SEEKING_CanSeekForwards

Return Values

Return Values

Returns the HRESULT value returned from calling IMediaSeeking::GetCapabilities on the connected pin.

Remarks

This member function implements IMediaSeeking::GetCapabilities by calling the IMediaSeeking::GetCapabilities method on the upstream output pin connected to the peer input pin. The pin that performs the seek operation will return the capabilities present in the pCapabilities parameter. These returned capabilities will then, in turn, propagate to calls made from CPosPassThru::GetCapabilities member functions in intervening filters.

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CPosPassThru::GetCurrentPosition

CPosPassThru Class

Retrieves the current position in terms of the media stream's total length.

HRESULT GetCurrentPosition(
  LONGLONG* pCurrent
  );

Parameters

pCurrent

Current position in current time format units.

Return Values

Returns NOERROR if successful. Otherwise, returns the HRESULT value returned from calling IMediaSeeking::GetCurrentPosition on the connected pin.

Remarks

This member function implements the IMediaSeeking::GetCurrentPosition interface. It calls the CPosPassThru::GetMediaTime virtual member function, which you should override and implement in your derived class to return the current position. If this fails (which it does by default), the IMediaSeeking::GetCurrentPosition on the upstream filter's output pin is called.

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CPosPassThru::get_CurrentPosition

CPosPassThru Class

Retrieves the current position in terms of the total length of the media stream.

HRESULT get_CurrentPosition(
  REFTIME* pllTime
  );

Parameters

pllTime

Returned start time as a double value in seconds.

Return Values

Return Values

Returns the HRESULT value returned from calling IMediaPosition::get_CurrentPosition on the connected pin.

Remarks

The start position is applied before the rate and therefore is the position at typical playback speed.

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CPosPassThru::GetDuration

CPosPassThru Class

Retrieves the length of time that the media stream will play.

HRESULT GetDuration(
  LONGLONG* pDuration
  );

Parameters

pDuration

Returned length of the media stream.

Return Values

Return Values

Returns the HRESULT value returned from calling IMediaSeeking::GetDuration on the connected pin.

Remarks

This member function implements the IMediaSeeking::GetDuration method by calling this same method on the upstream filter's output pin.

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CPosPassThru::get_Duration

CPosPassThru Class

Retrieves the total duration of the media stream.

HRESULT get_Duration(
  REFTIME * plength
  );

Parameters

plength

Returned length of the media stream.

Return Values

Return Values

Returns the HRESULT value returned from calling IMediaPosition::get_Duration on the connected pin.

Remarks

The duration assumes normal playback speed, and it is therefore unaffected by the rate.

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CPosPassThru::GetMediaTime

CPosPassThru Class

Retrieves the starting and ending media times.

virtual HRESULT GetMediaTime(
  LONGLONG* pStartTime,
  LONGLONG* pEndTime
  );

Parameters

pStartTime

Returned starting media time.

pEndTime

Returned ending media time.

Return Values

Returns an HRESULT value (E_FAIL by default).

Remarks

Override this virtual member function to return the current samples' media time. This represents the current position in terms of media time (for example, frame 20 of a total 130 frames).

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CPosPassThru::GetPositions

CPosPassThru Class

Returns the current and stop position settings.

HRESULT GetPositions(
  LONGLONG * pCurrent,
  LONGLONG * pStop
  );

Parameters

pCurrent

Start time in the current time format.

pStop

Stop time in the current time format.

Return Values

Return Values

Returns the HRESULT value returned from calling IMediaSeeking::GetPositions on the connected pin.

Remarks

This member function implements the IMediaSeeking::GetPositions method by calling this same method on the upstream filter's output pin. It allows the retrieval of several values with only one call.

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CPosPassThru::GetPreroll

CPosPassThru Class

Retrieves the preroll settings.

HRESULT GetPreroll(
  LONGLONG * pllPreroll
  );

Parameters

pllPreroll

Returned preroll time.

Return Values

Return Values

Returns the HRESULT value returned from calling IMediaSeeking::GetPreroll on the connected pin.

Remarks

This member function implements the IMediaSeeking::GetPreroll method by calling this same method on the upstream filter's output pin.

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CPosPassThru::get_PrerollTime

CPosPassThru Class

Retrieves the time prior to the start position that devices should start rolling.

HRESULT get_PrerollTime(
  REFTIME* pllTime
  );

Parameters

pllTime

Returned preroll time as a double value in seconds.

Return Values

Return Values

Returns the HRESULT value returned from calling IMediaPosition::get_PrerollTime on the connected pin.

Remarks

Preroll time is the time prior to the start position at which nonrandom access devices, such as tape players, should start rolling.

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CPosPassThru::GetRate

CPosPassThru Class

Retrieves the current rate.

HRESULT GetRate(
  double * pdRate
  );

Parameters

pdRate

Current rate, where 1 is the normal rate.

Return Values

Return Values

Returns the HRESULT value returned from calling IMediaSeeking::GetRate on the connected pin.

Remarks

This member function implements the IMediaSeeking::GetRate method by calling this same method on the upstream filter's output pin.

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CPosPassThru::get_Rate

CPosPassThru Class

Retrieves the rate of playback relative to normal playback speed.

HRESULT get_Rate(
  double * pdRate
  );

Parameters

pdRate

Returned rate.

Return Values

Return Values

Returns the HRESULT value returned from calling IMediaPosition::get_Rate on the connected pin.

Remarks

A rate of 1.0 indicates normal playback speed. A rate of 0.5 indicates half speed. A rate of –1.0 indicates normal speed in reverse.

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CPosPassThru::GetStopPosition

CPosPassThru Class

Retrieves the position at which the media stream stops.

HRESULT GetStopPosition(
  LONGLONG* pStop
  );

Parameters

pStop

Returned stop time.

Return Values

Return Values

Returns the HRESULT value returned from calling IMediaSeeking::GetStopPosition on the connected pin.

Remarks

This member function implements the IMediaSeeking::GetStopPosition method by calling this same method on the upstream filter's output pin. The stop position is a time between zero and the duration of the media at which playback should stop.

The stop position is applied before the rate and therefore is the position at typical playback speed.

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CPosPassThru::get_StopTime

CPosPassThru Class

Retrieves the time at which the media stream stops.

HRESULT get_StopTime(
  REFTIME* pllTime
  );

Parameters

pllTime

Returned stop time as a double value in seconds.

Return Values

Return Values

Returns the HRESULT value returned from calling IMediaPosition::get_StopTime on the connected pin.

Remarks

The stop time is a position between zero and the duration of the media at which playback should stop.

The stop position is applied before the rate and therefore is the position at typical playback speed.

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CPosPassThru::GetTimeFormat

CPosPassThru Class

Retrieves the current time format, which determines the format of units used during seeking.

HRESULT GetTimeFormat(
  const GUID * pFormat
  );

Parameters

pFormat

Media time format currently supported by this interface.

Return Values

Return Values

Returns the HRESULT value returned from calling IMediaSeeking::GetTimeFormat on the connected pin.

Remarks

This member function implements the IMediaSeeking::GetTimeFormat method by calling this same method on the upstream filter's output pin.

See the IMediaSeeking::IsFormatSupported method for a list of time formats.

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CPosPassThru::IsFormatSupported

CPosPassThru Class

Determines if a specified time format is supported.

HRESULT IsFormatSupported(
  const GUID * pFormat
  );

Parameters

pFormat

Time format to compare.

Return Values

Return Values

Returns the HRESULT value returned from calling IMediaSeeking::IsFormatSupported on the connected pin.

Remarks

This member function implements the IMediaSeeking::IsFormatSupported method. See that method for a list of valid time formats.

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CPosPassThru::IsUsingTimeFormat

CPosPassThru Class

Determines if the time format being used in the call is the same as the one currently in use by the interface.

HRESULT IsUsingTimeFormat(
  const GUID * pFormat
  );

Parameters

pFormat

Time format to check.

Return Values

Returns S_OK if pFormat is the current time format; otherwise returns S_FALSE.

Remarks

This member function implements the IMediaSeeking::IsUsingTimeFormat method by calling this same method on the upstream filter's output pin. This can be used in place of IMediaSeeking::GetTimeFormat to save copying the GUID.

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CPosPassThru::NonDelegatingQueryInterface

CPosPassThru Class

Returns a specified reference-counted interface.

HRESULT NonDelegatingQueryInterface(
  REFIID riid,
  void **ppv
  );

Parameters

riid

Reference identifier.

ppv

Pointer to the interface.

Return Values

Returns E_POINTER if ppv is invalid. Returns NOERROR if the query is successful or E_NOINTERFACE if it is not.

Remarks

Returns pointers to the IMediaPosition, IMediaSeeking, and IUnknown interfaces by default. Override this method to publish any additional interfaces implemented by the derived class.

This member function implements the INonDelegatingUnknown::NonDelegatingQueryInterface method.

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CPosPassThru::put_CurrentPosition

CPosPassThru Class

Sets the time that the media stream begins.

HRESULT put_CurrentPosition(
  REFTIME llTime
  );

Parameters

llTime

Start time expressed as a double value in seconds.

Return Values

Returns the HRESULT value returned from calling IMediaPosition::put_CurrentPosition on the connected pin.

Remarks

The start time is a position between zero and the duration of the media at which playback should begin when the next run command is issued. Do not call this method when the filter graph is running, only when it is paused or stopped.

Setting the start position when paused causes playback to resume from the new start position when the run command is issued.

The start position is applied before the rate and therefore is the position at typical playback speed.

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CPosPassThru::put_PrerollTime

CPosPassThru Class

Sets the time prior to the start position that devices should start rolling.

HRESULT put_PrerollTime(
  REFTIME llTime
  );

Parameters

llTime

Preroll time to be set.

Return Values

Returns the HRESULT value returned from calling IMediaPosition::put_PrerollTime.

Remarks

Preroll time is the time prior to the start position at which nonrandom access devices, such as tape players, should start rolling.

Note that while this member function passes the call upstream, the IMediaPosition::put_PrerollTime method is not implemented on any Microsoft source filter.

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CPosPassThru::put_Rate

CPosPassThru Class

Sets the rate of playback relative to normal speed.

HRESULT put_Rate(
  double dRate
  );

Parameters

dRate

Rate to set.

Return Values

Returns E_INVALIDARG if dRate is zero. Otherwise, returns the HRESULT value returned from calling IMediaPosition::put_Rate on the connected pin.

Remarks

This property allows an application to speed up or slow down playback relative to the normal default playback speed. A rate of 1.0 indicates normal playback speed. Specifying 2.0 causes playback at twice the normal rate: a video created for 10 frames per second (fps) will be played back at 20 fps, if resources permit. Audio streams played back at above-normal speed increase the pitch rather than drop frames.

Negative rates indicate reverse play. Not all media will support reverse play.

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CPosPassThru::put_StopTime

CPosPassThru Class

Sets the time at which the media stream will stop.

HRESULT put_StopTime(
  REFTIME llTime
  );

Parameters

llTime

Stop time as a double value in seconds.

Return Values

Returns the HRESULT value returned from calling IMediaPosition::put_StopTime on the connected pin.

Remarks

The stop time is a position between zero and the duration of the media at which playback should stop.

The stop position is applied before the rate and therefore is the position at typical playback speed.

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CPosPassThru::QueryPreferredFormat

CPosPassThru Class

Retrieves the preferred time format to be used by the interface.

HRESULT QueryPreferredFormat(
  GUID *pFormat
  );

Parameters

pFormat

Time format preferred by the interface.

Return Values

Returns the HRESULT value returned from calling IMediaSeeking::QueryPreferredFormat on the connected pin.

Remarks

This member function implements the IMediaSeeking::QueryPreferredFormat method by calling this same method on the upstream filter's output pin.

See the description for IMediaSeeking::IsFormatSupported for a list of available time formats. If the time format returned is not satisfactory, use the IMediaSeeking::IsFormatSupported method to query for supported time formats that you can use.

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CPosPassThru::SetPositions

CPosPassThru Class

Sets current and stop positions and applies flags to both.

HRESULT SetPositions(
  LONGLONG * pCurrent,
  DWORD dwCurrentFlags,
  LONGLONG * pStop,
  DWORD dwStopFlags
  );

Parameters

pCurrent

Start position if stopped, or position to continue from if paused.

dwCurrentFlags

When seeking, one of these flags must be set to indicate the type of seek. See the IMediaSeeking::SetPositions method for a description of these flags.

pStop

Position in the stream at which to quit.

dwStopFlags

Stop position seeking options to be applied. These are the same as listed for dwCurrentFlags.

Return Values

Returns the HRESULT value returned from calling IMediaSeeking::SetPositions on the connected pin.

Remarks

This member function implements the IMediaSeeking::SetPositions method by calling this same method on the upstream filter's output pin. It allows the retrieval of several values with only one call.

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CPosPassThru::SetRate

CPosPassThru Class

Sets a new playback rate.

HRESULT SetRate(
  double dRate
  );

Parameters

dRate

New rate, where 1 is the normal rate, 2 is twice as fast, and so on.

Return Values

Returns E_INVALIDARG if dRate is zero. Otherwise, returns the HRESULT value returned from calling IMediaSeeking::SetRate on the connected pin.

Remarks

This member function implements the IMediaSeeking::SetRate method by calling this same method on the upstream filter's output pin. It is an error to set the rate to 0.

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CPosPassThru::SetTimeFormat

CPosPassThru Class

Sets the time format, which determines the format of units used during seeking.

HRESULT SetTimeFormat(
  const GUID * pFormat
  );

Parameters

pFormat

Time format to be supported by this interface.

Return Values

Returns the HRESULT value returned from calling IMediaSeeking::SetTimeFormat on the connected pin.

Remarks

This member function implements the IMediaSeeking::SetTimeFormat method by calling this same method on the upstream filter's output pin. See the IMediaSeeking::IsFormatSupported method for a list of time formats.

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