[Chuck Reti]

David Pogue’s “Missing Manual” books have been published for all versions of OS X and macOS.
Good “how-tos” at osxdaily.com, support.apple.com/mac among dozens of others a search will turn up.

Chuck Reti
Detroit MI

[Chuck Reti]

You say you “updated” Onyx. Since you say you’ve installed El Capitan and not Sierra, you should be using the Onyx version for El Cap, which is v. 3.1.9 (the updated version for Sierra is v 3.2.5. If you’re on the proper version, go to ~/Library/Preferences/com.titanium.OnyX.plist. Delete that prefs file and try relaunching Onyx again.

[Chuck Reti]

What is the reason for viewers changing the channels, if exactly the same content is on every channel?
You would need to take video out of the computer, and (assuming you’re in the USA), convert to NTSC, Standard Definition not HD, and then into RF modulators for each and every channel, 2 through 13 VHF, and presumably each UHF channel as well, 14-51 (again, assuming you’re in the US).
You would essentially have to be equipped like an analog-era cable or closed-circuit TV head end. If the material is high-definition, a similar but more complicated process.
A closed-circuit TV systems integrator might be able to set you up, but very likely an expensive proposition.

[Chuck Reti]

Only one specifically for Mac OS I’ve seen lately is Softron’s “On The Air CG”. Info at
https://www.softron.tv/products/ontheair-cg
around $3.2K

[Chuck Reti]

I’ve tried the gel approach with varying degrees of success. Keeping it flat on the surface and not “crinkling” can be troublesome, and of course, it’s shiny, not matte finish like the flatscreen it’s on, so reflections can abound.
Once had an “oh by the way” where a projector was placed in the set to provide a wall-sized image. I did stick a couple of gels in the light path so the image wasn’t a bright blue blob.

[Chuck Reti]

I’ve encountered this many times. I have found no onboard monitor settings that came close to rendering proper color temperature, even when a “warm” setting and handles on RGB gains are available. The solution was to use inline RGB correction (the YUV correction available on our switcher AUX feeds do not offer the ability to correct monitor white balance).
We had QuStream units available for this purpose, but other solutions are available, such as units from Xintekvideo. I ‘m not familiar with the AJA LUT box, but that could also do the job. Very good reproduction can be had but it does take a bit of tweaking. I’ve also found that, even when well set up using a chip chart or monochrome staircase, greyscale tracking is generally not very good on most set monitors- a high APL image might look great but a darker image might go a bit reddish or bluish. You generally have to find a good in-between setting, both on the corrector and on the monitor, and make note of the settings values. You may also find that monitors of the same model by the same maker don’t match very well, so you may need separate correctors on each display.

[Chuck Reti]

My understanding is that the USB will revert to the speed of the slowest device on the bus. A hub merely extends the bus on the iMac that you”re plugged into. I don’t know if the different USB 3 ports on the iMac are separate buses or not. On past models they were not.
Depending on your model and it’s vintage, there possibly may be a device solution involving use of FireWire or Thunderbolt to create a USB bus separate from the internals.

[Chuck Reti]

The noise and horizontal lines suggest RF (Radio Frequency) interference somewhere in the signal path. Is your gear anywhere near to transmitters- broadcast radio, TV, two-way, Wi-Fi, cell relays etc.? Just a thought.

[Chuck Reti]

Though no longer in development, the Perian codec suite is still available from MacUpdate
Works fine for MP4 with Quicktime Player.
Also try VLC Media Player.

[Chuck Reti]

I’ve had a few instances of problems caused by a dead or nearly-dead Logic board battery. Done a PRAM zap?