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INTRODUCTION.
The Black Box AV Director DVR blends the simplicity of a standard video tape recorder with the
versatile control features of a digital record and playback machine. The DVR can operate under simple
manual control via the hand controller but, when programmed via the Sequence Builder, the DVR
becomes a complete ‘Show Control’ system with frame accurate control of lighting, mains switching
and general-purpose logic signals.
RECORD OPERATION.
The DVR records a composite PAL video + stereo audio directly onto hard disc.
The live analogue video signal is digitally encoded into a CCIR-656 data stream (720 * 576 @ 25
frames/sec) and then compressed using 'wavelet' technology into frame 'packets' of fixed size. The
stereo audio is sampled (32KHz: 16 bits/channel) via an audio codec and added to the video data to
form a complete a/v frame packet of 128kBytes size. The frame packets are then stored directly to the
hard disc in real time.
The compressed video frame size is controlled by varying the 'compression factor' in response to the
amount of detail present in the picture. A servo mechanism maintains the best possible picture quality
whilst ensuring that the frame size does not exceed the maximum.
The hard drive is addressed in terms of frames (i.e. 128Kbyte units), and recording can begin at any
point within the total disc space. The frames are stored sequentially on the hard drive and a display
readout indicates the current record position in terms of hours:minutes:seconds:frames.
Recording can be started manually from a wired remote control, or via the RS232 computer interface
or via a pre-programmed schedule (real time clock built in).
Time-lapse recording is possible by specifying gaps between captured frames.
A 'long-play' mode allows recording of a single field per frame and storage into 64kByte packets. This
doubles the total record time available on the disc at the expense of a halving of vertical resolution, the
picture quality however is acceptable for many applications.
An 'off-line' audio dub facility allows a separately recorded 'audio only' section to replace the existing
sound track recorded with the video.
PLAYBACK OPERATION.
Playback is the reverse operation of record. The compressed data is decoded into a CCIR-656 data
stream which is fed to a video DAC to provide both PAL encoded composite video and analogue
RGB signals. The audio data is fed back to the codec to reproduce the analogue audio.
Playback can begin at any point on the hard drive containing recorded data. Once again the start point
is defined in terms of hours:minutes:seconds:frames i.e. playback is frame accurate.
Freeze frame, scan forward and back, and slow play are available.
Playback is controlled via the wired remote, the RS232 computer interface or via a pre-programmed
schedule.
