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#16
07-12-2019, 07:14 AM
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Not sure I understand your comment, but when playing a Macrovision tape thru a switcher, the tape is just a source, and nothing is modified on it during playback. If you wanted to preserve the switcher's modification of the signal, you needed to make a recording of the switcher's output.
The only machine/format that could modify the signal that was actually on the tape would be a digital format, for example D2, which had a pre-read function. By playing with the signal flow from the various heads, you could read-before-write and do things like add titles to an existing tape. Preview copiously, because once you press record, you're committed. Like jumping off a cliff with a parachute; you might land safely, but there's no turning back. 
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#17
07-12-2019, 07:33 AM
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I'm curious about the "Many video production switchers of the day would either discard and rebuild the vertical interval, or allow you to do a 'wipe' that excluded the source's vertical interval from the switcher's output. "
Would such a device make it easier for the set to sync? And presumably strip out any offending additions to the blanking interval?
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#18
07-12-2019, 08:01 AM
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It's standard practice in vision mixers (production switchers in the US) to replace the entire sync and blanking interval. This ensures that the output has consistent sync, burst and blanking. Hence VBI information will not normally pass through a vision mixer.
Same is true in a SDI environment. If a system needs to pass embedded packets these are normally passed through a sidechain. Often decoded and re-encoded. Most timebase correctors will also replace the entire sync and blanking interval. Back in the 1990s/early noughties I designed a number of TBC/frame synchronisers for G2 Video Systems. We weren't supposed to mention that they would effectively remove macrovision. Our official line when asked about macrovision was "not something we've considered or tested". This was actually true, we hadn't thought about it in the design and I'm not sure we ever ran any formal tests. It's just people found that it did remove macrovision  Hence both vision mixers and TBCs will usually remove macrovision.
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#19
07-12-2019, 12:32 PM
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While these professional devices will actually remove Macrovision, it's a high-overhead way to do it, in terms of size, complexity and power.
In my years of captioning in the analog domain, I often had to guide editors through the task of modifying video content without disturbing existing captions. That led to the 'wipe from line 22 on down' technique of preserving the VBI information (captions, Nielsen codes, etc.) but replacing visible picture. (For example, this was often used to create 'tagged' spots with individual retail locations from one previously-captioned master.) Doing the opposite had the spin-off effect of disabling Macrovision. So like Jeff, it was not our primary goal. The challenge in the digital age is verifying which equipment will faithfully throughput (or record/playback) caption data that is in the VANC area of the digital signal. Some extremely popular gear will not. Other popular gear from the same manufacturer will. So I always have to vet the chain of equipment after caption insertion to guard against unpleasant surprises. Not a Macrovision thing, but my caption equipment can set or reset the record flag in the digital signal. But in a similar vein, my (pro) HD-SDI recorders don't pay attention to that flag, and will record anything. Last edited by Chip Chester; 07-12-2019 at 12:35 PM.
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#20
07-12-2019, 02:52 PM
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Quote:
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Linear Mode
