Yes, PLL == Phase Locked Loop.
OK, I did a quick look at Wikipedia and TBC isn't what I was thinking of. TBC done digitally would require sampling the video signal and need enough RAM to buffer it and then reproduce it at the right rate.
So a VHS signal has a 5MHz bandwidth so we'd need to sample at 10MHz minimum. Each field is 1/60 second. So assuming an 8-bit resolution and an ADC with a built-in 1k buffer (just the first thing that google shows), we could get 1,000 samples every 10,000,000/1000 = 0.1ms. An arduino can handle that interrupt rate, so the only immediate issue is choosing one that has enough RAM to buffer the 1,000 samples. Next, you have to send those samples to a video DAC at the standard field rate (this is the whole point of the TBC).
The above is an oversimplification based on some quick googling, but I think that with good external hardware, it can be done with an arduino. Now, of course, the question is since we have to add an external ADC (the internal arduino one isn't close to being fast enough) and an external DAC, then why use the arduino at all, and not just a bare microcontroller?
The answer to that question is left as an exercise for the grasshopper 