Vela CineCast 2000-0422, Инструкция по установке и эксплуатации

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Chapter 2 — Overview and Operation 131
MPEG PLAY Command (With Frame Counting)
Pre-Black
This is an eight-bit pre-black interval in video frames. A value of 0h uses default
pre-black of 1 (display first frame). Minimum pre-black is one frame. Pre-black
frames can be set to 1 if the MPEG file starts on a Group of Pictures (GOP)
boundary, i.e., starting on a closed GOP.
When starting on an open GOP, the first few frames of video must be blank — this
is called “pre-black,” and refers to the number of black frames before the start of
visible video. This blackout is necessary to allow the MPEG decoder hardware
time to reconstruct the first few frames of video. Video macro-blocking would be
evident at start-up if pre-black was not used.
When starting on an open GOP, use a pre-black value of 3. This will blank the first
two frames and display the third frame.
Frame Count
32-bit frame count in video frames. Video/audio will play back for this specified
number of frames. A value of 0h uses the maximum frame count. Note that the
total frame count includes pre-black and visible frames, such that
Frame Count = Specified Preblack Visible Frames.
Post-Black
16-bit post-black interval in video frames (30Hz). A value of zero uses the
default of 8 frames. The specified post-black period is required in applications of
back-to-back playback. This allows time for the host to queue up the one to two
MB of data for the next playback, and allows the decoder time to initialize, load
MPEG data, and start-up the MPEG decoder hardware. Currently the minimum
post-black interval is six frames.
Total black time between back-to-back videos
The total black time between videos must be at least eight frames.
Total Black = Pre-black + Post-black
≥
8 Frames.
Thus, the smallest valid values of pre- and post-black are:
Pre-black: 2 & Post-black: 6 or
Pre-black: 1 & Post-black: 7
NOTE: A combination smaller than eight “Total Black” will still produce eight frames
of black.
Special Cases – Playback End
The end of playback can occur in a few different ways, depending on where the
terminal frame occurs.