When is full-frame TBC not needed?
It has never been completely clear to me, but if when using virtualdub you aren't seeing any dropped frames or vertical jitter, I don't know why you would benefit from a full frame TBC. If there are periods of time where it takes too long for the next frame to arrive, virtualdub will just "insert" a null frame which just says to keep displaying the last good frame. This is basically what a frame TBC also does, you just don't know that it happened because the TBC doesn't tell you statistics. What a TBC can do that virtualdub can't (if your capture card doesn't tolerate the frames being that close together to capture both), is space out frames that arrive too close together, preventing a dropped frame.
Again, my theory with "frame TBC should not be used" only applies if you aren't seeing any "dropped frames" in virtualdub's statistics. The argument FOR a full frame TBC is that you don't want to have to repeat a capture because you start seeing dropped frames halfway through the capture and don't want to repeat the whole capture again, so I'd normally use one anyway if there are a lot of transfers to do. ....But if you've captured something like 20 VHS tapes with a certain hardware chain, all with no dropped frames, without a full frame TBC, and you aren't having audio sync issues or vertical jitter, the benefit of a full frame TBC is extremely questionable for me (with that specific hardware capture chain). Logically, adding a full frame TBC would actually be HARMFUL in the above situation as they do impart conversion losses as they go from analog to digital then from digital back to analog. Thoughts? |
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What a frame TBC does is right there in the name: timing correction. The video is input, and RAM buffers release temporally timed to perfection. Only when a signal is awful does a TBC fail to properly time to 29.97 or 25. Even "weak (frame) TBCs" tend to properly released at the proper internal, and the "weak" part manifests as visual distortions. Non-TBC frame syncs attempt to time based on a rudimentary clock, with low/no buffer. Those are what tend to give up with milliseconds (ms) and insert/dupe. Sometimes drop, if the insert/dupe range has to expand too far. Quote:
If I close my eyes, you can't see me? :question: Quote:
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As I stated elsewhere, too much is made of A>D>A, mostly by people that have limited TBC knowledge, or have experienced bad hardware. A key tenet of a quality TBC is transparency, meaning it functions without you seeing any ill effects. Some have it, many do not. When you dumpster dive TBCs, and start to dive into TBC(ish) items, transparency falls off a cliff. All TBCs add some % of processing noise (in test patterns), but quality TBCs tends to be drowned out by the tape noise, or the VCR noise, or capture card noise. And "noise" here refers to everything from geometry to color accuracy, not a narrow definition of "noise" (so not grain, or electrical, or whatever). To borrow from my favorite crass TBC analogy, the frame TBC is like a condum/rubber, the line TBC is like the pill/IUD. To be protected (from bad captures), you need both. Without any protection, you get STDs and unexpected crotch goblins (aka dropped frames, audio sync issues, etc ~ bad captures). Lots of people tempt fate here, and many (most?) lose that game of Russian roulette. |
:p The comparisons are pretty funny on this thread.
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