Vitc Reader Operations - AEC PCIe-TC User Manual

VITC READER OPERATIONS

PCIe-TC boards use proprietary hardware and software to read VITC from
the signal present at "VIDEO IN" connector J3. Depending on the VITC
signal quality, which varies greatly from one tape machine to the next,
our PCIe-TC boards can read VITC at tape speeds from -10x to +10x play
speed, including step frame and still frame situations.
The VIDEO input signal is first passed through a differential low pass
filter/amplifier to remove high frequency noise and common mode noise.
This cleaned up VIDEO input signal can be viewed at the "LPFVID" test
point on the board (includes a +1.4V DC offset). This signal is then DC
restored and passed through an analog comparator to convert the analog
waveform into a digitized VITC input signal, which is then analyzed us-
ing a combination of hardware and software to extract the desired time
bits, user bits, and embedded bits information.
The VIDEO input automatically adapts itself to whatever analog video
standard is present (14 total, see specs). No setup work needs to be done.
That said, analog EDTV and HDTV signals do not have VITC on them.
If you are having trouble reading VITC, first try the bootable test/demo
program on the PCIe-TC CDROM. Be sure the cable and connectors you
are using are of good quality and are wired correctly. Use a continuity
tester if necessary to check them out. Connect one end of the cable to the
VIDEO input on your PCIe-TC board (J3), as described in the INSTAL-
LATION section of this manual. Connect the other end of the cable to the
"VIDEO OUT" connector on the VTR (or other signal source).
VITC data is normally recorded on two nonadjacent lines in the vertical
interval of a SDTV video signal. Lines 10-20 are used with NTSC/SMPTE,
and lines 6-22 are used with PAL/EBU. Normally the PCIe-TC board will
automatically select the first two lines it sees which have VITC on them.
You may override this feature by writing or using custom software which
tells the board which two lines to read. This is necessary in cases where
there are two sets of VITC in the vertical interval, or when other VITC-
like signals are present in the vertical interval and are confusing our board
software. The "PCIe-TC Board Reference Manual" explains how to do
this.
PCIe-TC User Guide Page 16 April 2012
VITC READER OPERATIONS
(continued)
The PCIe-TC board can read VITC from most tape machines at speeds
ranging from -1x to STILL to +3x play speed. At other than play speed,
some VTR's destroy portions of vertical interval signals. Since our soft-
ware has been written to ignore bad video signals, the results may not be
entirely satisfactory. Please call us if the board works fine at play speed,
but will not read VITC under any other conditions. A board software
modification may be in order.
Most tape machines, when outputting video at other than play speed, will
cause wide streaks (dark lines) to appear on the video picture. These
streaks, if they happen to go through the vertical interval area, will make
the VITC data unreadable. If at STILL or PAUSE, you may have to jog
the tape slightly until the VITC is OK (not in a streak). If the tape is
moving, VITC can usually be read OK. In general, the more streaks you
see, the smaller are your chances of reading VITC reliably.
Ideally, the tops of the VITC pulses should be near +80 IRE (0.57V), and
the bottoms of VITC pulses should be near +0 IRE (0.00V). Also, the
horizontal and vertical sync tips should be near -40 IRE (-0.28V).
If the video signal which is carrying VITC has been low pass filtered be-
low 4MHz, the VITC signal may become attenuated and/or distorted to
the point where it is unusable, even though the sync still looks OK. This
is often a problem with the VHS tape format, which usually works OK at
play speed with first generation ("original") tapes, but which quickly be-
comes unusable if you have copied one VHS tape to another, for example.
Refer to the "PCIe-TC Board Reference Manual" if you need technical
information on register mapping, VITC line number selection, how to read
time code from the board, etc..
PCIe-TC User Guide Page 17 April 2012