1080p High Bitrate or 4K Low Bitrate?

[huster091]

I made a 2k DCP to find out that the Blu-ray had HDR. I did try to reencode HDR to SDR but that didn't go so well, so here I am asking the community.
Should I just get a high bitrate 1080p Blu-ray (since they don't have HDR), or a low bitrate 4k that will be downscaled to a 2k DCP.
Unfortunately atm I can't test out both options so I'm asking here.

[IoannisSyrogiannis]

What you need to avoid, is HDR, isn't it so?
The most common case with UHD Blu-Ray discs is that they are as well HDR. I have come across UHD editions that weren't. If you can find that, take advantage, I -for one- don't think downscaling is necessary.
Since in most cases, though, you will have to go with HD (to avoid HDR) the downscaling dilemma won't be troubling you much.

If, by any chance, you transcode a short excerpt of a UHD in both 4K and 2K, feel welcome to share your findings, along with details such as DCP bitrates.

[Carsten]

Until proper UHD/HDR DCP transcoding is sorted out, I would always use standard 1080p Blurays as a source.

[huster091]

I -for one- don't think downscaling is necessary.

I have to, the projector is 2K, so there is no need to make it in 4K just for the projector to downscale it (I would rather save the space).
However, I might try to compare a 1080P Remux, and a non-HDR 4k downscaled to 2K DCP, just to see if there are any noticeable differences.

along with details such as DCP bitrates

I use the default 200 Mbits/s, is that wrong?

[Carsten]

200MBit/s is perfectly okay, that's a good set-and-forget number.

How would I find out that a UHD/4k Bluray is non-HDR? It's probably nothing they would actually advertise on the cover?

- Carsten

[huster091]

How would I find out that a UHD/4k Bluray is non-HDR? It's probably nothing they would actually advertise on the cover?

If it's a 4k Bluray, it probably has HDR, to know just play it on VLC and press CTRL + J, in Stream 0 see if there are any indications to:

• Max. luminance
  Min. luminance
  Primary R
  Primary G
  Primary B
  White point
  MaxCLL
  MaxFALL

If u find these, the video is HDR, if not then it's SDR.
Another way to know is from the PGS subtitles, on an HDR Bluray, the subtitles are pretty dark (They won't be if played on HDR screen), unlike the SDR Bluray's subtitles who will always be bright.

[IoannisSyrogiannis]

There is no "wrong" with bitrates, apart from very high (going higher than 230), when some media blocks find it hard to keep up. There are some that don't sweat it unless more than double that, but good practice don't use such bitrates, unless HFR is involved.
200Mbps for 2K and 2D is a waste of data, though. That is a difference of view we have with Carsten. If you'd rather save the space and the source is a Blu-Ray, as you write, go half, if not lower.

[huster091]

So let's say I have a 1080p Bluray Remux (around 30-40 GB), what's the bitrate you would recommend?

[IoannisSyrogiannis]

Is it Tykver's "Run Lola Run" or Bela Tar's "Satantango"? We are talking about bitrate (so, duration makes a difference).
I won't give you another number, I already wrote that if I were you, I would go 100 Mbps if not lower. I have written in the past about the matter of bandwidth here, if you want something to read on the matter.
If you care for images of frames, on top of that, you may have a look here.