IltmmConvert::SetPreferredFilter

#include "ltmm.h"

C Syntax	HRESULT IltmmConvert__SetPreferredFilter(pConvert, FilterType, Val)
C++ Syntax	HRESULT SetPreferredFilter(FilterType, Val)

IltmmConvert *pConvert;	/* pointer to an interface */
long FilterType	/* value for a filter type */
BSTR Val;	/* string */

Sets a preferred filter (decoder or demultiplexer.

Parameter	Description
pConvert	Pointer to an IltmmConvert interface.
FilterType	Value that indicates filter type. For a list of possible values, refer to ltmmConvert_PreferredFilter Constants.
Val	String that has the following possible values: Display Name of the filter Friendly Name of the filter ltmmFilter_LEADDefault (this will use the default LEAD filter) ltmmFilter_DontCare (this is the same as setting the value to NULL) NULL (don't use any preferred filter - revert to the default DirectShow filter) For a list of possible values, refer to ltmmFilter Constants.

Returns

S_OK	The function was successful.
<> S_OK	An error occurred. Refer to the Error Codes or the HRESULT error codes in the DirectShow documentation.

Comments

By default, the toolkit uses filters according to the default DirectShow mechanism, which assigns a merit to each filter. The filters with the highest merits are tried first. If they fail, the filters with a lower merit are tried next until a combination of filters is found that can handle the graph. However, sometimes 3rd party filters get installed on some computers with a high merit and are used instead of the filters you shipped with your application. And unexpected problems can occur if these filters are not working properly. The SetPreferredFilter method allows you to control which filters are used in your application. You can decide to use a certain decoder, demultiplexer or you can choose to use only the LEAD filters.

DirectShow filters have a friendly name and a display name. The friendly name is easy to remember and is usually displayed by GraphEdit or other filter enumeration utilities. But there can be more than one filter with the same friendly name, so it is safer to use the display name, since no two filters have the same display name.

Display names for software filters have the following format: @device:sw:GUID\GUID.

For example Microsoft’s “MPEG-2 Splitter” has:

friendly name: MPEG-2 Splitter

display name: @device:sw:{083863F1-70DE-11D0-BD40-00A0C911CE86}\\{3AE86B20-7BE8-11D1-ABE6-00A0C905F375}.

The display name for a particular filter can be obtained from the "DirectShow Filter List Utility" shipped with the toolkit. See Examples Programs and Demos for Win32/x64 for more details.

If the FilterType argument is equal to ltmmConvert_PreferredFilter_Generic, then the possible values for Filter are: ltmmFilter_LEADDefault or ltmmFilter_DontCare.

If ltmmFilter_LEADDefault is specified, then the LEAD default decoders and demultiplexers will be set for ALL of the values listed in ltmmConvert_PreferredFilter.

If ltmmFilter_DontCare is specified, then the internal list of the preferred filters will be cleared and the DirectShow filter merit determines which filters will be used.

Use the ltmmFilter_XXX constants whenever possible. See ltmmFilter Constants for a list of predefined values.

Required DLLs and Libraries

LTMM

For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application.

Platforms

Win32, x64, Mobile

Elements:	IltmmConvert::GetPreferredFilter
Topics:	Multimedia Function Groups
	ltmmFilter Constants
	ltmmConvert_PreferredFilter Constants