CSourcePosition Class

CSourcePosition is an abstract class that assists source filters with the implementation of IMediaPosition methods.

Derive from this class and set the duration and default stop positions. This class supports IMediaPosition, and calls the pure virtual member functions CSourcePosition::ChangeStart, CSourcePosition::ChangeStop, and CSourcePosition::ChangeRate when CSourcePosition::put_CurrentPosition, CSourcePosition::put_StopTime, or CSourcePosition::put_Rate is called, to allow a source filter to handle these commands and start sending new data.

Override the CSourcePosition::ChangeStart, CSourcePosition::ChangeStop, and CSourcePosition::ChangeRate member functions to do something when the properties change.

Protected Data Members

Name	Description
m_Duration	Duration of the stream.
m_pLock	Pointer to a CCritSec object for locking.
m_Rate	Sample rate.
m_Start	Start time.
m_Stop	Stop time.

Member Functions

Name	Description
CSourcePosition	Constructs a CSourcePosition object.

Overridable Member Functions

Name	Description
ChangeRate	Override this pure virtual to handle notification that the rate property has changed.
ChangeStart	Override this pure virtual to handle notification that the start position property has changed.
ChangeStop	Override this pure virtual to handle notification that the stop position property has changed.

Implemented IMediaPosition Methods

Name	Description
get_CurrentPosition	Not currently implemented.
get_Duration	Retrieves the total duration of the media.
get_PrerollTime	Not currently implemented.
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	Not currently implemented.
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.

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CSourcePosition::ChangeRate

CSourcePosition Class

Override this member function to handle notification of a change of sample rate.

virtual HRESULT ChangeRate( ) PURE;

Return Values

Returns an HRESULT value that depends on the implementation. HRESULT can be one of the following standard constants, or other values not listed:

Value	Meaning
E_FAIL	Failure.
E_POINTER	Null pointer argument.
E_INVALIDARG	Invalid argument.
E_NOTIMPL	Method isn't supported.
S_OK or NOERROR	Success.

Remarks

This member function is called when a change to the rate has been made by a call to IMediaPosition::put_Rate. Override this and change the rate of data sent; typically, this will be by a call to CBaseInputPin::BeginFlush and CBaseInputPin::EndFlush, and then sending samples marked with new time stamps.

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CSourcePosition::ChangeStart

CSourcePosition Class

Override this member function to handle notification of a change of start time.

virtual HRESULT ChangeStart( ) PURE;

Return Values

Returns an HRESULT value that depends on the implementation. HRESULT can be one of the following standard constants, or other values not listed:

Value	Meaning
E_FAIL	Failure.
E_POINTER	Null pointer argument.
E_INVALIDARG	Invalid argument.
E_NOTIMPL	Method isn't supported.
S_OK or NOERROR	Success.

Remarks

This member function is called when a new start position has been requested by a call to IMediaPosition::put_CurrentPosition. Override this and change the data sent; typically, this will be by a call to CBaseInputPin::BeginFlush and CBaseInputPin::EndFlush, and then sending samples marked with new time stamps.

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CSourcePosition::ChangeStop

CSourcePosition Class

Override this member function to handle notification of a change in stop time.

virtual HRESULT ChangeStop( ) PURE;

Return Values

Returns an HRESULT value that depends on the implementation. HRESULT can be one of the following standard constants, or other values not listed:

Value	Meaning
E_FAIL	Failure.
E_POINTER	Null pointer argument.
E_INVALIDARG	Invalid argument.
E_NOTIMPL	Method isn't supported.
S_OK or NOERROR	Success.

Remarks

This member function is called when a change to the stop position has been made by a call to IMediaPosition::put_StopTime. Override this and ensure that the correct stop time is being observed; typically, this will be a call to CBaseInputPin::BeginFlush and CBaseInputPin::EndFlush, and then resending data.

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CSourcePosition::CSourcePosition

CSourcePosition Class

Constructs a CSourcePosition object.

CSourcePosition(
  const TCHAR * pName,
  LPUNKNOWN pUnk,
  HRESULT * phr,
  CCritSec * pLock
  );

Parameters

pName

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

pUnk

Pointer to the owner of this object.

phr

Pointer to an HRESULT value for resulting information.

pLock

Pointer to a CCritSec object used for locking.

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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CSourcePosition::get_CurrentPosition

CSourcePosition Class

Currently not implemented.

HRESULT get_CurrentPosition(
  REFTIME* pllTime
  );

Parameters

pllTime

Returned start time as a double value in seconds.

Return Values

Returns E_NOTIMPL.

Remarks

Override this method if you can return the data you are actually working on. The start position is applied before the rate and therefore is the position at typical playback speed.

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CSourcePosition::get_Duration

CSourcePosition Class

Retrieves the total duration of the media stream.

HRESULT get_Duration(
  REFTIME* plength
  );

Parameters

plength

Returned length of the media stream.

Return Values

Returns E_POINTER if pLength is invalid. Otherwise, returns S_OK.

Remarks

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

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CSourcePosition::get_PrerollTime

CSourcePosition Class

Validates the pointer, but the preroll retrieval is not currently implemented.

HRESULT get_PrerollTime(
  REFTIME* pllTime
  );

Parameters

pllTime

Returned preroll time as a double value in seconds.

Return Values

Returns E_POINTER if pllTime is invalid. Otherwise, returns E_NOTIMPL.

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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CSourcePosition::get_Rate

CSourcePosition Class

Retrieves the rate of playback relative to normal playback speed.

HRESULT get_Rate(
  double * pdRate
  );

Parameters

pdRate

Returned rate.

Return Values

Returns E_POINTER if pdRate is invalid. Otherwise, returns S_OK.

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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CSourcePosition::get_StopTime

CSourcePosition 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

Returns E_POINTER if pllTime is invalid. Otherwise, returns S_OK.

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.

---

CSourcePosition::put_CurrentPosition

CSourcePosition Class

Sets the time within the media stream that playback should begin.

HRESULT put_CurrentPosition(
  REFTIME llTime
  );

Parameters

llTime

Start time expressed as a double value in seconds.

Return Values

Returns an HRESULT value from the call to CSourcePosition::ChangeStart.

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.

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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CSourcePosition::put_PrerollTime

CSourcePosition Class

Not currently implemented.

HRESULT put_PrerollTime(
  REFTIME llTime
  );

Parameters

llTime

Preroll time to be set.

Return Values

Returns E_NOTIMPL.

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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CSourcePosition::put_Rate

CSourcePosition Class

Sets the rate of playback relative to normal speed.

HRESULT put_Rate(
  double dRate
  );

Parameters

dRate

Rate to set.

Return Values

Returns an HRESULT value from the call to CSourcePosition::ChangeRate.

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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CSourcePosition::put_StopTime

CSourcePosition 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 an HRESULT value from the call to CSourcePosition::ChangeStop.

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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