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IOTA-VTI Operation Manual
Video Frame, Field Type and Frame Central Timing
The video stream has codes to identify an even field type from an odd field type, and IOTA-
VTI can read the field type code and action the 10th millisecond display to put the timing for
the Even field on the Left and Odd field on the Right.
However it is not consistent how video camcorders, video grabbers and DVRs sequence the
field order when assembling video frames. It appears that the sequencing method;
a) (even+odd), (even+odd), is the most common
b) (odd+even), (odd+even), is somewhat less common
c) some will even assemble a pseudo frame from (even+even), (even+even) fields, and
actually ignore the odd fields, (or vice versa). Obviously this method is not desirable
because ½ the data the camera sees is tossed away by the recording equipment.
IOTA-VTI has the means to demonstrate and identify field type.
This is the method;
-
Start IOTA-VTI and display the time screen on a video monitor or similar.
-
Remove the cover to reveal the PCB. Next to the DIP switches you will find two
sites marked 5Spare and 6Spare.
-
Using a metal probe e.g. tweezers, as shown in photo above, either the even or
odd fields can be temporarily nulled.
-
Probe 5Spare will null odd fields and you will see the right 10th millisecond
display disappear.
-
Probe 6Spare will null even fields and you will see the left 10th millisecond display
disappear.
-
If during this test you can see only one 10
either 5Spare or 6Spare, it disappears with one probe, and nothing happens when
probing the other, then you know your recording equipment is of the type c) above
and is doing you an injustice by throwing away ½ your data.
Finally make a brief recording and examine the 10
-
If the earlier time is on the left then your recorder is of the type a) above.
-
If the earlier time is on the right then your recorder is of the type b) above.
- 9 -
th
millisecond display and when probing
th
millisecond display.
Video Timers
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