Why is over/undercranking in SD technically impossible?

[Barry_Green]

According to the manual (PDF pg. 35, you can also record VFR in 24P or 30P at 720. But on the previous page, the manual seems to contradict itself, and says something about "without the use of a frame rate converter", it must be PN mode.

Can somebody clarify this?

The 720pN mode includes a hardware frame rate converter. The 720p mode doesn't. If you shoot in variable frame rates in 720pN mode, you see immediately the slow-mo or fast-mo effect. If you shoot vfr in the 720p mode, you won't see the effect until the footage has been processed through a frame rate converter (either hardware or, far more commonly, software).

 

[sycophant]

Variable frame rate SD would be a lot more possible on P2 than with tape, as P2 can write a variable rate. So it would be possible capture more images (say 60) per second, and then simply record them in a row (with associated timecode and such) into a DV stream. It would work, but could still be an engineering headache (timecode is a potential problem).

But I think the demand is probably fairly low, so maybe not worth the effort.

Doing it on tape would present a huge problem as the tape has to run at a constant speed, say 25fps where I live, if we were sampling 50fps, we'd start to have huge buffering issues. The tape would have to be run at the right speed to allow frames to be recorded as they are shot or else you just end up buffering horribly.

Varicam is different, as it shoots 60fps constantly, so the tape is always running at that speed. Record 30fps and it simply records frames to the tape as they are sampled and repeats that frame until a new one arrives. Problem is that post-processing is required to achieve the correct playback speed.