SetPreferredFilter Method

Summary

Sets a preferred filter (decoder or demultiplexer)

Syntax
C#
VB
C++
public virtual void SetPreferredFilter( 
   PreferredFilter filterType, 
   string val 
) 
Public Overridable Sub SetPreferredFilter( _ 
   ByVal filterType As PreferredFilter, _ 
   ByVal val As String _ 
)  
public: 
virtual void SetPreferredFilter(  
   PreferredFilter filterType, 
   String^ val 
)  

Parameters

filterType
A PreferredFilter enumeration value specifying the desired filter type

val
String with the following possible values:

  • Display Name of the filter
  • Friendly Name of the filter
  • PreferredFilters.LEADDefault (this will use the default LEAD filter)
  • PreferredFilters.DontCare (this is the same as setting the value to NULL)
  • NULL (don't use any preferred filter - revert to the default DirectShow filter)

Remarks

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.

Starting with Windows 7, there is also a list of preferred filters for certain media types. These filters will be used by default instead of filters with higher merit.

3rd party filters can also get installed on some computers with a high merit and might be used instead of the filters you shipped with your application. Unexpected problems can occur if the Microsoft preferred or the 3rd party 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 specific decoder or a 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.

val is a string for the Display Name or Friendly Name of the filter. If Friendly Name is used, this function will choose the first filter it finds with the specified friendly 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" (ltmmListFilters.exe) shipped with the toolkit. See Examples Programs and Demos for Win32/x64 in the Multimedia API help file for more details.

If the filterType parameter is equal to PreferredFilter.Generic, then the filterName parameter's possible values are: PreferredFilters.LEADDefault or PreferredFilters.DontCare. If PreferredFilters.LEADDefault is specified, then default decoders and demultiplexers will be set for all values listed in PreferredFilter. If PreferredFilters.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.

It is recommended that you use the constants from Constants.PreferredFilters whenever possible.

Example
C#
VB
using Leadtools; 
using Leadtools.Multimedia; 
using LeadtoolsMultimediaExamples.Fixtures; 
 
public bool _result = false; 
public ConvertCtrlForm _form = new ConvertCtrlForm(); 
 
public void ConverterPreferredFiltersExample() 
{ 
   ConvertCtrl convertCtrl = _form.ConvertCtrl; 
 
   try 
   { 
      // set the preferred ISO Demultiplexer to the LEAD default (which is the LEAD ISO Demultiplexer) 
      convertCtrl.SetPreferredFilter(PreferredFilter.ISODemultiplexer, Constants.PreferredFilters.LEADDefault); 
 
      // the default ISO Demultiplexer should be the LEAD ISO Demultiplexer now 
      // filter names are not case sensitive, so ignore case in the compare 
      _result = (string.Compare(convertCtrl.GetPreferredFilter(PreferredFilter.ISODemultiplexer), 
                 Constants.PreferredFilters.ISODemultiplexer, true) == 0); 
   } 
   catch (Exception) 
   { 
      _result = false; 
   } 
} 
Imports Leadtools 
Imports Leadtools.Multimedia 
Imports LeadtoolsMultimediaExamples.Fixtures 
 
Public _result As Boolean = False 
Public _form As ConvertCtrlForm = New ConvertCtrlForm() 
 
Public Sub ConverterPreferredFiltersExample() 
   Try 
      ' reference the forms capture control 
      Dim convertCtrl As ConvertCtrl = _form.ConvertCtrl 
 
      ' set the preferred ISO Demultiplexer to the LEAD default (which is the LEAD ISO Demultiplexer) 
      convertCtrl.SetPreferredFilter(PreferredFilter.ISODemultiplexer, 
                                     Leadtools.Multimedia.Constants.PreferredFilters.LEADDefault) 
 
      ' the default ISO Demultiplexer should be the LEAD ISO Demultiplexer now 
      ' the filter names are not case sensitive, so do ignore the case in the compare 
      _result = (String.Compare(convertCtrl.GetPreferredFilter(PreferredFilter.ISODemultiplexer), 
                                Leadtools.Multimedia.Constants.PreferredFilters.ISODemultiplexer, True) = 0) 
   Catch e1 As Exception 
      _result = False 
   End Try 
End Sub 
Requirements

Target Platforms

Help Version 20.0.2019.11.25
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