This filter acts on the output of the Telecide filter (or any other stream of progressive frames derived from a de-telecined clip) and deletes extra duplicated frames, while enforcing a desired decimation ratio. For example, suppose Telecide has been used to produce a clip containing progressive frames derived from 3:2 pulldown material. Decimate can take the processed clip as input and delete the duplicated frames by deleting one frame out of each group of five. Actually, because VirtualDub filters cannot delete frames, Decimate writes an Avisynth script that is used to do the actual frame deletion. It is acknowledged that this is a cumbersome procedure. The next generation of VirtualDub will allow filters to delete frames. Avisynth is available from a link given on the main page of the site at the bottom of this file. Version 0.3 (not 1.0 beta 3) is the most stable and reliable version. Later betas are now available from third parties (other than the original author Ben Rudiak-Gould) that may be perfectly usable.
First, detailed instructions for using Decimate are given, then the options are described. The following example is for 3:2 pulldown removal.
AVISource("d:\don\test.avi")
Obviously, the specified clip should be the same one that was input to Decimate.
DeleteFrame(1)
...
The filter has the following configuration options:
Path for Avisynth delete script: Use the Browse button to specify the destination path and filename for the output script. If no filename is specified, an Avisynth script will not be generated, but the DebugView option (see below) will still function. This would be useful for tweaking the threshold before generating the final output file.
Decimate 1 in: Set this option to N to remove one of every N frames. For example, for a 12fps source that was doubled up to 24fps and then sped up to 25fps for PAL transmission, you'd enter 2 to restore it to 12 fps. Decimate 1 in 5 is useful for removing 3:2 pulldown. Decimate 1 in 25 is useful for removing PAL pulldown in which 24fps material is telecined to 25fps. The maximum number that can use is 50. If you enter more than 50, it will be changed to 50 when you hit OK.
DebugView: If the DebugView checkbox is checked, the filter outputs processing information that is viewable using the DebugView utility that is available on the home page of the web site given below. This information, while possibly interesting to an end user, is designed to assist filter development.
Please note that the frame numbers shown are the absolute frame numbers in the source clip. They do not correspond to the frame numbers used in the Avisynth DeleteFrame() lines because as each frame is deleted all the following frame numbers reduce by one.
Thanks to Simon Walters for suggesting the idea of writing Avisynth scripts to delete frames (VirtualDub filters cannot delete frames). Thanks to James Lin for proposing to simply delete the most similar frame in the set of N frames.
For additional information, version updates, and other filters, please go to the following web site:
Filters for VirtualDub
http://sauron.mordor.net/dgraft/index.html
Donald Graft
December 31, 2001
(C) Copyright 2001, All Rights Reserved