Merging VCube, Руководство пользователя

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Appendices : PullUp - PullDown Page 238
Inter Frame:
MPEG with groups of pictures (GOPs). The use of GOPs is a very efficient way to compress video. But for post pro-
duction purposes, intra frame codecs are to be preferred since every frame is individually encoded, allowing
instant access with a lower computional overhead.
VCube features a DV codec (compression ratio ~ 1:5) and a MJPEG codec (possible compression ratio from 1:2.4 to
1:23) if required during capture or render processes.
Audio
Since video media can also feature a sound track, audio data flow must be added to the video streaming require-
ments.
PullUp - PullDown
One of the key features of VCube is the capability of changing the playback speed of Clips.
This function allows VCube to accomplish both PullUp and PullDown operations.
PullDown
All the story is around the NTSC video standard. In the NTSC world, a second lasts 1001 mS. That means that 30 fps
(SMPTE norm) media is displayed at 29.97 frame per second. This conversion is called pulldown.
• • VCube can convert a 30 fps Media to 29.97 fps : In the Timeline (29.97 fps) select the Clip(s) you need to
change the frame rate properties of. Double-click on the selection to display the Clips Information page.
Here, the speed can be set to 99.9% (PullDown). Once done, the Clip(s) length remains the same in the
Timeline. Now 1 frame will be missing every 1001 frames. You can use the Clip's handle to extend the Clips
duration reflecting their new fps value.
• Film production in the NTSC zone uses 24 to 23.98 fps conversion to facilitate transfers to tape etc.. In this
case, the speed value is also 99.9% (PullDown). With this new frame rate an integer number of film frames
corresponds to an integer number of video (NTSC) frames for telecine. This telecine technique is called the
3:2 pulldown. There are 4 frames of film for every 5 frames of NTSC video.
PullUp:
Is the reciprocal process. 1001ms becomes one second.
Drop Frame
Drop Frame is a SMPTE TimeCode format that counts 30 frames per second continuously but drops 2 frames from
the count every minute except for every tenth minute (I.e. it drops a total of 108 frames every hour) to maintain
synchronization of TimeCode with clock time. This is necessary because the actual frame rate of NTSC video is
29.97 frames per second rather than an integer 30 frames.
VCube displays "drop frame" TimeCode in this form 00:00:00;00 Notice the semi-colon separator before the frames
instead of the normal colon.