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lordsmurf 08-23-2016 03:13 PM


Originally Posted by sanlyn (Post 45100)
Some models do, some don't. You have to adjust brightness and contrast to achieve safe yuv levels during capture anyway. Once you have a capture with valid levels, you can tweak further in post processing.

^ Correct. :2cents:

The chipsets vary a lot, unit to unit, over the past 15 years.
It can also vary a lot base on on the source -- VHS, Hi8, digital cable, etc.

RS456 07-30-2020 05:35 PM

Can someone who owns the green AVT-8710 open it up and take the backside picture of both the boards? I think it is very possible to recreate this board and device. Who knows we can probably deal with the TBC shortage .

lordsmurf 07-30-2020 05:51 PM


Originally Posted by RS456 (Post 70477)
I think it is very possible to recreate this board and device. Who knows we can probably deal with the TBC shortage .

Nope! Not even close. The good chips are 15-20 years old, and no longer made. It's also not solely about chips, but on-chip software. So you'd be reinventing the wheel with more modern hardware, newly written firmwares. I've worked with several people that tried to recreate TBCs. It's not easy. To date, all projects have failed. In fact, at this very moment, I'm working with a developer. It's probably the closest that things have gotten yet, but it's still in R&D/prototype stages, at least 6 months away, if it even happens.

BTW, most green AVT-8710s have sanded chips. So nothing can be read.

hodgey 07-30-2020 08:17 PM

From what we've documented in other threads, the AVT uses SAA7114 video decoder chips for decoding the analog video, the TBC-3000 (and possibly the TBC-1000 as well) use the older SAA7111. They're both off-the-shelf video decoders that were used in tons of stuff, but are now discontinued, though it seems they're still available second hand. It seems NXP, who last had the license for them stopped making video decoder chips in general.

The video chips output decoded video data in YUV 422 format with 720 pixels per line (or RGB but I don't think that's used here, and possibly also raw 8-bit CVBS, but that may or may not be only for VBI). They also have some additional outputs for sync signals (can also be embedded in the video output as described in ITU-R_BT.656). Most analog video decoder chips work in a similar manner.

In the TBCs this seems to be hooked up to some memory chips, which are then hooked up to a FGPA chip. This is where any custom processing would happen (if any). The AVTs also have a separate ROM chip hooked up to it, which presumably contain code to run on the FPGA. The FPGA presumably also translates key presses to commands to the video chips. The TBC-3000 seemed to have some FPGA chip or microcontroller with embedded ROM + some simple logic chips as well.

This is then hooked up on the other side to another memory buffer, and then to an off-the-shelf video encoder chip that converts digital component data to an analog signal. On a modern alternative one would probably want to output to HDMI, SDI or over USB as a capture device instead, no reason to turn it back to analog.

There isn't really so much magic going on here, if there are custom settings on the video decoder, it would be possible to read it off the serial connection pins of the chip. The FPGA may have some logic to decide on how to deal with data that comes in too fast or slow, but I don't see a whole lot that could be done with it. It's the video decoder chip that's doing the brunt of the work, and these chips originally made by philips are quite good at that. It's possible to dump ROM chips as well, but that gets into possible copyright infringement territory.

There are some other companies making analog video decoder chips still, Analog devices even has chips with built in line and frame TBC functions (provided it's hooked up to some memory.) Whether it's as robust as the Philips/NXP chips I don't know, it may be something that could work as a "modern" solution. I know some people on videohelp (not sure if they're here as well), have used their Eval boards as a TBC/Capture device of sorts.

Renesas and TI also still makes video decoder chips, but I don't know if they're as advanced.

lordsmurf 07-31-2020 06:31 AM


Originally Posted by hodgey (Post 70480)
Analog devices even has chips with built in line and frame TBC functions (provided it's hooked up to some memory.) Whether it's as robust as the Philips/NXP chips I don't know

All information to date has shown that it's not. There are also multiple AD chips. The most damning instances are when HD cards have used the chips, yet completely falter on untimed SD input. This has been tried multiple times in the past decade, and each project is eventually abandoned. Note that the AD chips pre-date EOL'ing by Cypress and DataVideo, who exited the TBC market due to chips needed no longer be fabbed, supplies ran dry. I would think either, or both, would have jumped on AD had it been a solution.

Remember: TBC is a wide term, and marketing often rapes it.

The AD chips have contained various weasel terms like "ADLLT" and "mini TBC" to describe what actually happens in-chip. That doesn't inspire much confidence. And again, indy projects have all failed to date, and the TBC makers apparently didn't see those as viable alternatives before EOL'ing all TBCs.

I recently postulated something else sinister, when it comes to HD cards. You know how Blackmagic and Magewell cards can drop/repeat frames, even with frame TBC (ie, DataVideo TBC-1000) in the workflow? Odds are good that it's TBCs clashing. The AD-chip TBC is so weak on-card that the SD input fails. But the external frame TBC conflicts with the on-board wimpy TBC, to create the drop/repeat effects. I don't know why I had never thought of this scenario, but it's one I've run into with VCR TBCs, DVD recorder TBCs, and external TBCs.

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