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Variable Frame Rate (VariFrame)/
Shooting Ramps
Recorders supporting VariFrame are able to distinguish
between so-called valid and invalid frames.
When using variable frame rate/speed ramps, the link
speed (standard frame rate in the video menu) set on
the camera and on the recording system has to be
higher or equal to the maximum speed that will be
used. When a recording is started, camera and recorder
then "talk" at this link speed, which ensures that the
HD-SDI connection is maintained. The camera keeps
sending frames at the set link speed even while the
actual frame rate, at which it captures new images, is
lower. Every time a new image is captured, the output
image is updated. The difference between captured
fps and link speed is filled up with duplicates of the last
exposed frame. These duplicates are tagged as invalid
frames, causing a recording system with VariFrame
support to either not record these frames or skip
them during playback (depending on the recorder).
VariFrame tagging can be used for different applications.
The D-21 also uses VariFrame to mark even and odd
frames in the HD422 dual link/high speed output.
Note: Even though VariFrame allows recording
e.g. with link speed set to 30PsF and mirror
shutter speed set to 25 fps, this mode is not
recommended for standard operation.