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Using preprocessing filters

Standard motion picture film is shot at 24 fps. When motion picture film is recorded to video, it is put through a telecine process where frames are added that convert it to 30 fps for NTSC format so that it can be viewed on a television screen.

When video, such as a game show or news broadcast, is prepared for broadcast on television screens it is interlaced. Interlacing is necessary because television screens only display half of the horizontal lines in a frame, first the odd, and then the even.

Displaying video that has been telecined or interlaced on a computer monitor can result in flickering or streaking because computer monitors use a progressive display format, displaying one line after another in quick succession.

Windows Media 8 Encoding Utility includes filters that enable you to improve the quality of telecined and interlaced content on progressive-scan displays by removing the extra frames and deinterlacing the content before it is encoded. The filter that you apply depends on the source of your content.

This table describes the filters that are available.

Command Description
-v_preproc 0 No filters are applied. This is the default and can be used with content that is already in a progressive-scan format.
v_preproc 1 Deinterlaces the content, but preserves its size. For example, it takes 640 pixels by 480 pixels and 30 fps interlaced content and encodes it at 640 by 480 by 30 fps progressive-scan format.
v_preproc 2 Deinterlaces the content, but delivers half the original video size. For example, 640 by 480 and 30 fps interlaced content would be encoded at 320 by 240 and 30 fps progressive-scan format.
v_preproc 3 Deinterlaces the content, but delivers half the original video size and doubles the frame rate. For example, 640 by 480 and 30 fps interlaced content would be encoded at 320 by 240 and 60 fps progressive-scan format.
v_preproc 4 Deinterlaces the content, but delivers half the original vertical size and doubles the frame rate. For example, 320 by 480 and 30 fps interlaced content would be encoded at 320 by 240 and 60 fps progressive-scan format.
v_preproc 5 Converts the video from 30 fps to 24 fps using the inverse telecine filter.

The final quality of the encoded video depends on many issues, including the filters you apply and the technique that was used to create the source film or video. If you are unsure about the source of your content, then use the -v_preproc 0 filter. If, after applying the -v_preproc 0 filter, you see telecine or interlace artifacts, encode the content again using the –v_preproc 1 deinterlacing filter.

The inverse telecine filter is designed to detect and repair 3:2 pattern breaks in your content. These pattern breaks are also called incoherencies. If you know that your content came from a film source that was telecined, use -v_preproc 5. If there are telecine artifacts in the encoded content, and you don't know whether the telecine process was coherent, encode the content again using the -v_preproc 1 deinterlacing filter.

On rare occasions, using the -v_preproc 5 filter on content that has a consistent 3:2 pattern can result in minor telecine artifacts being introduced into the encoded content. For some high-quality applications, even a single telecine artifact in an entire movie is unacceptable. In these situations, and when you know that your content is coherent, you can set a registry key that will put the inverse telecine filter into "coherent mode." In coherent mode, you specify the frame in the 3:2 pattern where the shot begins. The inverse telecine filter will assume that the telecine pattern begins with that frame and is coherent, making no pattern-break adjustments at any time.

Coherent mode is disabled by default. To enable this feature, use the registry editor to locate the registry key HKEY_CURRENT_USER\SOFTWARE\Microsoft\Scrunch\WMVideo\Coherent Content For Inverse Telecine, and then set the DWORD value of this registry key to the appropriate value. The registry values correspond to the five frames in the telecine pattern, which are represented as AA, BB, BC, CD, DD. The first letter in each of these two-letter combinations represents the odd or top field of a frame, and the second the even or bottom field.

The following table shows the registry values that correspond to each of the five frames in the 3:2 pattern.

Value Description
0 Coherent mode is disabled.
1 The first frame in the clip is AA.
2 The first frame in the clip is BB.
3 The first frame in the clip is BC.
4 The first frame in the clip is CD.
5 The first frame in the clip is DD.

To set coherent mode to begin with frame BC, for example, you would set the DWORD value of the registry key to 3.

Note   You should only edit the registry if you are an advanced user. It is strongly recommended that you do not edit any other values in the registry. For more information about the registry, see Windows Help.

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