Camera Quick Tip: Using DSLRs with TriCaster
December 09, 2015 by Chuck Baker
Many modern DSLR cameras can record video at several resolutions and frame rates, some including 1080i or 1080p HD and higher. Of particular interest, however, is that some of these DSLRs are also able to provide the video live to their output port. A DSLR with this capability becomes attractive for users who may want to gain a savings versus getting more expensive dedicated video cameras, or who want to have the advantages of a camera that can do both very high resolution stills and HD video, plus have the huge range of lens options that DSLR cameras can provide.
DSLR cameras that are equipped with a mini-HDMI output port and can provide live output resolutions including 1080i or 1080p/30fps video can easily be used with the TriCaster Mini HDMI models, with the proper mini-HDMI-to-HDMI cable. With other current TriCaster models or with older models that support SDI, a converter such as HDMI-to-SDI would be preferred. With TriCaster 40 or some older analog-input TriCaster models, some form of HDMI-to-Analog converters may be needed. Check the specifications of your TriCaster model to determine your best choice for converters.
Understanding Latency and Best Practices
There is a critical difference to keep in mind between video cameras and DSLRs. Dedicated video cameras are optimized to reduce latency, the time it takes from light entering the lens to a video signal coming out the output port. Shooting video is an “extra feature” for DSLR cameras so there is not the concentration on optimizing the video processing pipeline speed in the design of the hardware and software. For this reason, many DSLR cameras have high latency - in other words, the image takes a long time getting through the signal path. Depending on your production needs, you may need to account for this latency in your workflow.
For example, you would not want to use DSLRs if you are doing a live event that includes sending the action on-stage to large display monitors for the audience present at the event. This is a common arrangement for live concerts and for House of Worship setups. High latency means images on the displays are well behind what is happening on stage, and also out of sync with live audio coming from the stage, both of which can be disconcerting for the audience. On the other hand, if you are not projecting to a display in the event venue but are simply streaming out the video of your live event or worship service to an online audience, the delay does not matter, so using DSLRs would be fine.
When you are able to use DSLRs, the best practice is to use all the same model of DSLR cameras, so that latency is essentially the same from all the cameras. Mixing DSLRs of different makes and models or DSLRs with standard video cameras will mean that a given frame of the action will arrive at TriCaster inputs at different times from each camera. TriCaster has a frame sync capability, so it can correct for signal timing differences so that you can switch among the cameras without a jarring glitch in the video, but you may be switching to different points in the action unless you also compensate for that. Delay lines on the cameras with lower latency times may be able to help with that issue.
Another timing issue likely to arise with DSLRs: if audio is being captured by separate microphones and audio equipment, then sound from a given point in the action will reach TriCaster ahead of the images from the DSLR cameras. TriCaster includes a solution for this: audio can be delayed on a channel-by-channel basis to match up with the video on each input.
Check for Overlays on Output
With some makes of DSLRs, the camera may by default have some form of overlay on the video output. For example, the Canon EOS 7D includes the interface and focus box overlays on its HDMI output, and does not natively offer controls to remove these. However, the user can install the third-party open-source Magic Lantern firmware on the camera (this is not Canon-blessed and may void the warranty), which provides controls to remove the interface overlay and to AutoHide the focus box. So, overlay on the video output, and what you can do about it, is also an issue that you will want to investigate with regard to any DSLR you are considering for video use.
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