HPX170/HVX200a/HMC150: Confused about capture, processing, and recording frame rates

DavidNJ

DavidNJ

Carbonite Member
I moved this since it was getting no answers on the technical subforum... The literature says all processing takes place in 1080p60 format...then down rezzed for storage or output.

However, how are the different frame rates processed? Is 720p24 handled at p60? If so, how? Are the variable rates? If so, how does it create the different capture rates? Are they all blended?

I note that the variable rates are only available in 720p. Why if processing is all at 1080p60?

Thanks,

David
 
720pn for variable from rates. Good question re: 1080i . . . probably best answered by an engineer (or one of the many threads on this topic). I'd bet it has something to do with what the electronics are able to handle, 1080 has a lot more 1's and 0's that have to be handled rather swiftly than 720.

Nobody (as far as I know) does variable frame rates in a sub 10k camera . . . but who cares, just shoot 1080 and use your software to manipulate it to your hearts content, no?
 
Lets see if I can answer most of these questions:

You can use the HPX/HVX to capture different frame rates, but you can't ramp the frame rates. I think the lowest end camera tha does ramping is the Varicam.

The camera does all its capturing at 1080 on progressive chips, however, the codec the camera utilizes:
Right now every HD brodcaster in America is sending out a 1080i signal or a 720p signal. There supposedly isnt enough bandwith in cable/satelite to send out a 1080p signal. So with this in mind, the HPX/HVX series cameras use a Panasonic's brodcast codec: DVCProHD which follows those conventions:

A. it always has to run at a 59.97 or 29.98. At 1080 the 100mb codec is interlaced, this means that it can shoot 60i, 30p (by splitting the progressive frame into two interlaced fields, then putting them back together in post) or 24p; Again by splitting the progressive frame, only this time a bit more math goes into it and you either get a 3:2 pulldown or a 2:3:3:2 pull down (24pa).
Even if the camera reads everything at 1080p60 DVCProHD itself is an interlaced format and so can only support a maximum of 30progressive frames.

Enter 720p. DVCProHD supporst 720p60 which broadcast standard that allows for 60 progressive frames. This allows for very interesting action (60p played back at 60p) or for slow motion (60p played back at 30p or 24p). Normally with the Varicam you'd shoot slow motion (the camera itself is always recording 60 frames) and it would flag the correct frames for later. You could use the FCP plug in, or the Panasonic deck, to the watch the slow motion footage at the correct playback speed.
The HPX/HVX cameras introduced native recording: since we're recording to solid media there is no need to mantain a constant tape speed (the main reason to always shoot 60 frames) so the camera only records the flagged frames to the media. This allows you for the first time to actually play back in the field your slow motion footage for review. This also means that the camera only records the frames you set, which means less leeway in post. You can't add frames to any undercranking since those frames are simply not there.
 
The chips get reclocked to whatever rate the user selects. It's true that all internal processing is done at 1920x1080p, but it's not true to say that it's done at 60p. It's done at whatever frame rate you choose, *up to* 60p. So if you're shooting 1080/60i, all internal processing is indeed done at 1920x1080x60p, and then sliced into fields for recording. But if you're shooting 24p, the chips are reclocked to 23.976 fps, and all internal processing is then done at 1920x1080x23.976fps. If you choose 40fps, the chips scan at 40Hz and all processing is done at 1920x1080x40fps, etc.
 
So if i shoot 1080 24pA or 1080 25p the camera captures everything progressiv. But will there be interlacing artefacts? Can i transcode DVCPro to Prores for example and get true progressive frames without loosing resolution because of deinterlacing? Thanks!
 
Yes, 1080/24pA and 25p are shot as progressive. If you strip the pulldown out of the 24pA footage you're left with a pure 24p progressive file with no interlacing of any type.

And you should never de-interlace progressive footage.
 
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