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5. Switcher

If you don't need to mix video sources (lightboard + powerpoint, for example) you may not need a Video Switcher at all.

This page is an intro to the Video Switcher (Blackmagic Design ATEM Television Studio Production Switcher).  The Switcher control panel is an onscreen adaptation of hardware switchers that video production people are familiar with. User manuals tend to assume that familiarity, and don't explain the basics much.

Below are instructions for mixing the lightboard video with powerpoint graphics, displaying the sum on the presenter's monitor, and recording to disk.  It also explains a split-screen use, in which the lightboard occupies part of the image and a macro camera (or other live source) occupies the other.

We normally just add the brightness of the powerpoint graphics to that of the lightboard camera, which is why both are on black backgrounds to start with.  If you want to get fancier, there are ways to have the Switcher combine these images so that the powerpoint graphics appear to be behind the presenter, or in front of the presenter. Details are at ADVANCED SWITCHER MODES.

Also, we recently started using a newer switcher (the HD model) which allows us to use the presenter's monitor not only to show the lightboard image and the powerpoint graphics, but also a teleprompter script, all superimposed. Details are at TELEPROMPTER mix.

Video mixing panel

Below is the "switcher" panel of the Blackmagic Design ATEM software, which controls video mixing. 

The switcher recognizes up to six video inputs (Cam1 through Cam6), plus there is an all-black pseudo-input (Blk). 

For us, Cam6 is the videocamera that is permanently aimed at the lightboard.  Cam2 is a portable videocamera that we sometimes use for macro shots (e.g. photographing someone's hands as they build circuits), or for "talking head" closeups.

A computer running powerpoint provides graphics, and Cam1 is the video from this computer. We want to be able to superimpose Cam1 on any other video source, especially the lightboard, and this is done with the Upstream Keyer.  The right side of the panel above shows how the Upstream Keyer is configured: its Fill Source and Key Source are both set to Cam1, and the button for Pre Multiplied Key is selected.   This can be set up once and for all.  Now, when you want to superimpose the graphics, turn the keyer on/off with the KEY1 button.

The Preview/Program Transition Slider determines whether the video being recorded comes from the PROGRAM SOURCE bank of buttons, or from the PREVIEW SOURCE bank of buttons.   Typically we select Cam6 (the lightboard camera) on PROGRAM SOURCE, and Cam2 (the macro or portrait camera) on PREVIEW SOURCE.  

Very usefully, the Preview/Program Transition slider can be slid half way. If the transition type is WIPE (shown below), this allows us to split the screen, half lightboard and half macro, for instance.  There is far far more you can do with the ATEM switcher, for instance see the subpage on ADVANCED SWITCHER MODES. The above is usually all we use.

Audio mixing panel

The ATEM switcher control software also has an audio mixer panel:

Our wireless mic signals go into the audio inputs of the main videocamera (Cam6), and so its channel is the is the only one that I enable for audio on the audio mixer panel. Audio channels from all other cameras and laptops are disabled, so that we don't pick up unwanted sound.

I found that the ATEM switcher audio mixer's volume sliders don't work correctly, so I set them all at full volume (0 db), and I use other volume controls to adjust the audio level.  Specifically, I first set the wireless mic receiver's output volume control knob to about 50%. Then I set the videocamera's manual audio level to get a reasonable level on the ATEM audio tab's VU meters. Thereafter, to fine tune for different presenters, I only need to adjust the wireless mic receiver's output volume control knob, which is the one most easily at hand.

The VU meters on the ATEM's audio mixer tab should bounce into the red rarely, but get close often. But if I need to adjust this, I don't use the audio mixer's sliders, which are still defective (as of 2016).

Video "capture to file" tab

The ATEM switcher has a capture feature:

The built-in capture now works well (as of ~2015). It is important to set the recording format to "native", not "native progressive"

The video format is H.264 inside an "mp4" filetype. If your computer doesn't have enough RAM, or isn't fast enough, it won't be able to keep up with the stream for long.  If you want to check this file format, you can download a 3-second sample at the bottom of this page (videosample.mp4

Powerpoint graphics

To serve as an input to the switcher, your laptop HDMI output must be capable of driving a 1920x1080 monitor.  If the laptop cannot produce the protocol (e.g. 1080i30) that the Switcher is using, the Switcher will show it as black; there's no conversion, error message.  You can get this VGA to 1080p scaler.

Powerpoint slides should be on a black background, and the whole deck should be formatted to an aspect ratio of 16x9 before you start putting content on the slides (otherwise the content will get stretched when you reformat). Here is a template powerpoint deck you can start with. (You can also download it at the bottom of this page.)

For non-powerpoint sources where you don't get to choose the color scheme, such as web pages, it can be useful to Invert your laptop's display, changing white backgrounds to black, dark text to light, etc. On a mac, the Invert control is at System Preferences / Accessibility.

Video editing

I've been happy using a very simple editor, MPEG Streamclip, that works natively in H.264 format rather than "transcoding" the video up and back to other formats. Transcoding is slow, reduces video quality, inflates file size, and often messes up audio/video sync.

MPEG Streamclip allows you to trim clips or concatenate clips, and that's about all. After trimming, use "save as", not "export", to avoid transcoding.

You can directly upload these .mp4 files to youtube, vimeo, etc.  The H.264 encoding is what they like best.

Next: 6. FAQ

Michael Peshkin,
Sep 5, 2014, 9:11 AM
Michael Peshkin,
Sep 5, 2014, 8:59 AM