Sony DTV-01, Руководство пользователя

Страница: 14 / 132

17
24 Frames-per-Second Storage
In video, what appears to be a continuously moving image is actually a
series of discrete still pictures, called frames. Every video frame consists
of two interlaced “fields”, each of which contains half the frame’s scanning
lines. A U.S.-standard video picture runs at roughly 30 frames per sec-
ond. In contrast, movie file operates at 24 frames per second. So the
movies you see on television, cable or videocassette have all had their
frame rates converted by a special machine called a “telecine”.
The telecine converts the 24 film frames into video fields. However, video
requires 30 frames or 60 fields and Film is 24. Telecine performs this
process by converting 12 film frames to 24 fields (2 Fields/Film Frame)
and another 12 film frames to 36 fields (3 Fields/Film Frame). It is kept
seamless by converting one Film Frame to 2 Fields and the next one to 3.
This cycle is repeated 2, 3, 2, 3 until the 60 fields have been completed.
This Telecine process is called 2-3 Pull Down.
To achieve maximum recording time, the DVD-Video disc is actually mas-
tered in the original 24 film frame format. This reduces the video bit rate
by 20%, even before MPEG-2 encoding. During playback, the DVD-Video
player performs the 2-3 pull down function to generate a standard 30 frames
per second video output.