F

field

A portion of an interlaced video frame. NTSC provides a series of 59.94 interlaced fields per second, each separated by 1/59.94th of a second, with the scan lines of the even-numbered fields falling spatially halfway between the scan lines of the odd-numbered fields. No two fields are ever displayed on a television at the same time. You always look at either an even field or an odd field. Two interlaced video display methods are bob and weave.

Bob displays only one field at a time. In this mode, DirectDraw automatically shifts every other field by one half pixel vertically, and then stretches each field by a factor of two vertically.

Weave displays two successive fields at a time, where the resulting displayed image has horizontal scan lines that are alternately taken from the two fields. The fields are "woven" in a single frame. The top scan line of the displayed frame is the top scan line of the first field, the second displayed scan line is the top scan line of the second field, the third displayed scan line is the second scan line in the first field, and so forth.

The following diagram shows how fields are displayed in an interlaced source, using the bob and weave interlaced video display methods. In the diagram, top field refers to the odd, or first, field, and bottom field refers to the even, or second, field.

file writer

The section of a filter graph that consists of the multiplexer and file writer filters.

filter

A key component in the DirectShow architecture, a filter is a COM object that supports DirectShow interfaces or base classes. It might operate on streams of data in a variety of ways, such as reading, copying, modifying, or writing the data to a file. Sources, transform filters, and renderers are all particular types of filters. A filter contains pins that it uses to connect to other filters.

filter graph

A collection of filters. Typically, a filter graph contains filters that are connected to perform a particular operation, such as playing back a media file, or capturing video from a VCR to the hard disk.

Filter Graph Editor

A graphical tool included with the DirectShow SDK that creates and manages filter graphs. It enables you to easily create filter graphs by inserting filters, clicking, and dragging to form connections.

filter graph manager

A component that oversees the connection of filters in a filter graph, and controls the media stream's data flow. Filters must be connected in the proper order, and the data stream must be started and stopped in the proper order. The filter graph manager does this, and can also search for a set of filters that will render a particular media type and build its filter graph. When an application starts, pauses, or stops the media stream, plays for a particular duration or seeks to a particular point in the stream, the filter graph manager calls the appropriate methods on the filters to implement this stream control.

flushing protocol

A protocol that defines how filters flush data through the filter graph.

format type

A GUID value that indicates what a format block contains. DirectShow defines a number of major types, for example, the video type. These major types have a format block, such as VIDEOINFOHEADER, that describes the media data. The format block for a particular media type is specified by a GUID in the AM_MEDIA_TYPE structure. This GUID is called the format type. If the format block contains VIDEOINFOHEADER, the format type GUID will be FORMAT_VideoInfo.

frame blitting

Blitting (bit block transferring) media data to the client area of the application window on the primary surface.

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