4k footage in 1080p project

TRIFLIX Columbus, INPosts: 927 Enthusiast

Question 1: If I shoot 4k footage and set the project to 1080p can still increase the scale of the footage up to x 4 before loosing resolution?

Question 2: HitFilm seems to run much faster with 1080p footage than 4k footage, so would using the 4k footage in a 1080p project increase the speed as well?

Reason: I would like to shoot 4k so I can still do sublte zooms when using prime lenses but need to know how it will impact my post production time and exports.


  • Palacono
    Palacono Posts: 3,423 Enthusiast

    A1: Zoom would be x2, but yes.

    A2: Nope, it'll spend longer reading in the frames (video probably at a higher bitrate), decoding them, then resizing , or cropping them down to 1080p, so will be slower than using 1080p.

    But, it's worth shooting in 4k, resizing to 1080p - effectively using those as proxy files for the 4k - then if you do want to zoom in ,swap individual files out for the real 4k ones on those shots only.

  • Triem23
    Triem23 Posts: 20,603 Ambassador

    Answer 1: I'm interested to see staff response, but I think the answer is "it depends," because of Order of Operations. 

    I think 4k media in 1080p Comp Shot "A" maintains its original data, and for all animation purposes the original data are preserved. 

    However, once Comp A is embedded within Comp B the extra resolution is lost if Comp A is in 2D or 3D mode. The reason for this is Comp B is reading Comp A as a media clip and "prerenders" A. This is kinda the entire point of proxying a Composite Shot in the first place: changing a virtual media clip into an ACTUAL media clip.

    If Comp A is embedded in a 3D Unrolled mode, extra resolution should be available as Comp A cannot be reduced to prerendered media. 

    I believe this is how Hitfilm "thinks" as a side note Grade Layers are "flattened" or "prerendered" copies of the layers below. This is why masking a Grade Layer with a glow cuts out the glow, where a masked Plane with a glow has the glow extend around the mask--the mask has been moved in the layer's Order of Operations to be after effects. This is also why a Grade Layer can be selected as a source layer for varied filters. 

    Answer 2: No. The 4k footage contains (at least) four times the pixel data of the 1080 footage. This data must still be fully decided to be processed and/or displayed. In fact, scaling 4k footage in a 1080 timeline will slow performance more as the larger data must be decompressed, then scaled! 

    Of course, proxying the scaled footage improves performance, but, as discussed prior, this is because the Proxy is a rendered media clip. 

    Advice. Pre-planning only shoot 4k when you're planning for a move. If you know the shot is static, shoot 1080. If your camera allows, and you think you might just want a little movement--say a handheld shake without pan or zoom--split the difference and shoot 2.5k.

    The bottom line is this. In 2006 640x480 was the standard resolution for computer video. 1080p footage is 9 times the pixel data, and 3840x2160 footage contains 36 times the pixel data of a 640x480 stream. In that same time, CPUs, GPUs and storage (assuming SSDs) have all increased speed by about a ten-fold. 

    The practical upshot of this is editing 1080p footage is roughly as fast as working with 480p footage 10 years ago. 4k footage is going to be slower. A lot slower. 

    Note all the above assumes 8-bit/channel footage. Go to 10-bit, 12-bit or RAW and the problems compound. 12-bit 4k footage is 54 times the data of the 640x480 stream! 

  • NormanPCN
    NormanPCN Posts: 4,138 Enthusiast
    edited September 2016

    I also have questions/concerns about question 1. I think Hitfilm always uses the source and the scale is actually always a real scale (interpolation) operation and never a crop (+ possible scale depending on what you are doing). Hitfilm has no concept of cropping. Just scaling/interpolation.

    So the question is in Hitfilm when you have a 1080 project/window into a 4k file and your scale is > 100 does Hitfilm internally crop and scale the crop or does it just scale and then depending on the view you get whatever. 3D plane positioned in space or a 2D plane. The 2D plane is really a subset of the 3D. By that I mean unbeknownst to us a 2D plane in Hitfilm could be 3D and the axis position and camera view are adjusted as necessary to simulate 2D.

    I think this from experience with Vegas. It is fundamentally 2D, unlike Hitfilm. Vegas has a literal crop operator. That operation has an option to automatically scale the crop to fit the project dimensions. So if your crop of a larger source is a perfect fit to the project then the source pixels are untouched.

    Yes, Vegas has 3D track motion but that is completely separate and independent of the purely 2D cropping operation. In Hitfilm I think this is all one system. Hitfilm could special case and detect a zoom in crop and preserve source pixels exactly. That is special case to the generalized view positioning. Such a special case can be worthwhile. I once did a Ken Burns type slideshow and I had some massive crops or very large JPGs. This situation has problems with Hitfilm has they have media size limits so really big source media (> 4k, like stills) is probably first scaled to that internal limit and then your user controls settings.

    I've previously speculated that I think Hitfilm is treating 2D planes as textures on a GL surface. This is convenient but has issues with 100% perfect pixel accuracy since the 2D media is passing through the texture process. The most obvious thing is that stuff gets GPU AA treatment, and thus softened, when it really should not.

    With all that said, the interpolation from 4k to 1080 via a true scale, if that is what Hitfilm is doing, is very likely to look just fine. I assume Hitfilm is using a good/quality interpolation function.