Choose shutter duration, video standard and system frame rate
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- Andy Roberts (Deactivated)
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The SDI video standard frame rate and Vicon system frame rate must both be multiples of the same SMPTE base rate. The SMTPE base rates are 23.98 Hz, 24 Hz, 25 Hz, 29.97 Hz, and 30 Hz.
As shown in the following table, it is usually best to have the Vicon system rate higher than the video standard frame rate, so that the Vicon cameras can accurately track fast movement, but so the video cameras do not produce data at a rate that is higher than the PC can capture.
| Base rate (Hz) | SDI video standard | Vicon system frame rate (Hz) |
|---|---|---|
| 24 | 1080p / 24 (1x) | 96 (4x) |
| 25 | 1080p / 25 (1x) | 50 (2x) |
| 25 | 1080p / 50 (2x) | 100 (4x) |
| 29.97 | 1080p / 29.97 (1x) | 59.94 (2x) |
| 29.97 | 1080p / 59.94 (2x) | 119.88 (4x) |
Vicon Active Wands do not work at system frame rates below 50Hz.
When the system is set up in this way, the Vicon system strobes several times during each video frame. The active wand calibration device also strobes in sync with the optical system, so when the wand is moving, the video camera may see it in more than one place during each video frame. For this reason the shutter duration must be set within a particular range:
- If the shutter duration is set too low, the camera may not see the wand at all because the shutter is not open while it is strobing.
- If the shutter duration is set too high, the camera will see the wand in several places because the wand strobed more than once during the period the shutter was open.
The first situation is easy to spot by looking at the video screen on the camera. As long as the video is synced to the same source as the Vicon system, the strobes are clearly visible. If they are not, increase the shutter duration to cause them to appear.
The second situation is harder to spot. You can detect it by pausing live video of a wand wave in Shogun Live and carefully stepping through the video frames to look for multiple wands. Alternatively, set the shutter duration to a safe maximum value, as shown here:
| Base rate (Hz) | SDI video std | Video frame period (ms) | Vicon system rate (Hz) | Vicon frame period (ms) | Vicon frames per video frame | Safe max. shutter duration |
|---|---|---|---|---|---|---|
| 25 | 1080p / 25 (1x) | 40 | 50 (2x) | 20 | 2 | 1 / 60 = 16.7 ms |
| 25 | 1080p / 25 (1x) | 40 | 100 (4x) | 10 | 4 | 1 / 120 = 8.3 ms |
| 25 | 1080p / 50 (2x) | 20 | 100 (4x) | 10 | 2 | 1 / 120 = 8.3 ms |
| 29.97 | 1080p / 29.97 (1x) | 33.4 | 59.94 (2x) | 16.7 | 2 | 1 / 60 = 16.7 ms |
| 29.97 | 1080p / 29.97 (1x) | 33.4 | 119.88 (4x) | 8.3 | 4 | 1 / 120 = 8.3 ms |
| 29.97 | 1080p / 59.94 (2x) | 16.7 | 119.88 (4x) | 8.3 | 2 | 1 / 120 = 8.3 ms |
It might seem a good idea to reduce the shutter duration during calibration and then increase it afterwards for capture. However, this is not good practice because the shutter timing on the Blackmagic URSA 4K Mini is not center-aligned. In other words, the middle of the shutter-open time shifts as the duration is changed. If your video is always too dark, it may be better to reduce the Vicon system frame rate for calibration and increase it afterwards for capture, or choose a higher frame rate video standard.
Set up the video input device
- On the System tab, ensure the required frame rate is selected (Choose shutter duration, video standard and system frame rate).
- In theSystem Properties for the video input device, in the General section, ensure theEnabledandCalibrateoptions are selected.
- Under Timecode Setup, ensure that Use Timecode for Sync is selected.
- Ensure that the video standard is compatible with the Vicon system standard, and that there are no warnings such as this one:
- Ensure that the correct timecode is present on the video. You should be able to see it counting up.
Set up the connectivity device
- Go to theSystem Properties for the Vicon Lock unit, and in the Genlock and Timecode section, ensure thatGenlock Enabledis selected.
- Ensure thatGenlock Statusshows that the Vicon Lock unit is genlocked.
- Ensure that a valid timecode source is set for the Lock unit.
- Lock or Lock+ Set the timecode source to VITC.
- Lock Studio Set the timecode source to SDI.
- Lock or Lock+ Set the timecode source to VITC.
- On the Capture tab on the right, in theData Capturepanel, ensure that the system is genlocked and has timecode. This is indicated by two green circles.
If you are running at 29.97Hz timecode, ensure that drop-frame modes are compatible between the Vicon Lock and the video input device. For example, if the Lock shows this:
The video input should show this:
