Re: Genlock circuits

martin griffith wrote:
> On 4 Apr 2005 11:23:07 -0700, in sci.electronics.design
> vanagonvw@xxxxxxxxx wrote:
>
>
>>>It depends what you mean by "networks"
>>>Is it a computer network, or a whole pile of video destinations?
>>>What is the video reference for the multiple networks. If it is the
>>>same for all, you might be able to get away with analogue video
>>>delays. The CG, ir it is a reasonable one might be able to be timed
>>>into the system.
>>
>>>A bit more clarification would help
>>
>>Sorry.
>>
>>" Networks" are TV networks, CNN, FOX, etc. The goal is to send
>>crawling text from one character generator, out to multiple instances
>>of TV network feeds. The timing for each network is going to be unique
>>to each network feed.
>>
>>The CG is capable of genlocking to one feed, so I am soliticing methods
>>of an interface to allow its output to lock on to each network
>>independently. Not saying it can be done, but just trying to figure it
>>out in order to reply to the request.
>>
>>It may well end up being a reason to use many cheap CGs with genlock,
>>rather than trying to get by with one, or at least fewer, of the
>>rather costly ones that the client already offers. Of course,
>>considering the number of networks CATV delivers, its easy to see that
>>a "one CG" solution would be preferred from many points of view. Hoping
>>to find out if what they want is even reasonable.
>>
>>Thanks,
>>
>>John
>
> Ok, so all the I/C feeds are non sync. A Classic way would be to put a
> TBC/synchroniser on each feed, but it might be easier/cheaper to get a
> PC per video network that has a decent video codec and get appropriate
> software. I'm not in the video biz anymore, so I'd look at computer
> video grafix people, for an alternative approach.
>
> PC's are so cheap, but they will Never (IMHO) be as reliable as a
> hardware TBC / synchroniser. A PC that crashes wont go to a bypass
> mode and you would loose your network feed, but a TBC probably has
> that facility, so you would loose the caption, but not the network
>
> martin
>


It seems to me that each feed could be at any point in the video frame unless
the master transmitter/muxer was one unit with a TBC. So each "channel" could be
1/30th second out-of-time. This sounds like a 1-CG-per-feed kind of thing. Are
all the feeds the same programming, or different? And how many destinations?

The problem with any design which "sits there waiting to inject text" is the
device is active, inline with the signal path, 24/7. Any device (unless very
high quality (and complex and costly)) will degrade video quality, and if the
device fails, the signal could vanish or become corrupted - not a good thing.
Active bypassing could be implemented, but you might get glitches when switching
the CG Mux in and out. And some fault-tolerance is in order - perhaps even a
simple relay to "bypass" the entire feed if a fault is detected, but having a
fault like this could drive a video tech bonkers. Sounds like a fun project. :)

I'm by no means an expert, so take my ramblings with a grain of salt. :)

p.s. Many people dislike scrolling junk on the screen. Same with logos, ads,
channel numbers, etc. A surprising number of older folk can't read it, so if the
text is important, consider making it big and high-contrast.
.

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