does AF100 output variable frame rates through SDI?

M

mikebarber

Active member
Is it correct that the AF100 doesn't output variable frame rates via SDI? If not, is it technically possible? I am under the impression that it is (otherwise how does the Nano do over/under cranking?).
 
The AF100 outputs either 1080/24pSF or 1080/60i on its HD-SDI. If you shoot variable frame rates, it will embed the footage within its 1080/60i signal -- so any variable frame rate from 1 to 30, yes, will be output in such a way that you can extract the native frame rate footage.

However, HD-SDI doesn't support data rates more than 30p, so it's simply not possible for the AF100 to output it. Instead it will output as fields, turning each frame into a field and outputting that (with appropriate field duplication for proper pulldown).

So no, you're not going to be able to output 1080/48p out the SDI (because HD-SDI can't output that, and the Nano can't record it anyway). But you could do from 1 to 30.
 
AFAIK that's correct, because VFR is not part of the SDI spec, which means that the Nano etc. can't record overcrank (not sure about under).
 
If you know your way around After Effects you could consider recording the AF100 in 60i mode and outputting from the HD-SDI to a 60i file on a computer or external recorder, then turning the 60i into 60p (actually very simple) and then having the slow-mo you want. Granted this would require you shoot in the proper shutter as well. Also you'll loose some resolution in conversion of the fields to 60p, but you'll be recording in 422 and at a higher bit-rate via the HD-SDI than the on-board would allow. I think the results would be much better than the on-board but that's up for debate.
 
Why jump through the hoops though? Why not just record on the onboard SDHC card? It already has increased quality because the AF100 increases the bitrate when recording variable framerate footage.

External recording would give you 4:2:2, but duplicating fields would cut that back to 4:2:0 anyway, so really there's no point...
 
Barry_Green said:
Why jump through the hoops though? Why not just record on the onboard SDHC card? It already has increased quality because the AF100 increases the bitrate when recording variable framerate footage.

External recording would give you 4:2:2, but duplicating fields would cut that back to 4:2:0 anyway, so really there's no point...
Click to expand...
The appeal of capturing in an interframe edit ready codec like ProRes is really the biggest appeal for me, but I see what you mean about losing colour sampling etc...

I was curious, because I was hoping Samurai and or Ki Pro Mini would be able to support VFR... the Nano claims to support over/under cranking, wasn't sure how.
 
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