Reconsidering 4K/UHD Classification Logic

[theguymadmax]

Current Implementation

Jellyfin currently identifies 4K/UHD content using only a horizontal width threshold of 3800px. This single-dimension approach may be missing legitimate high-resolution content.

Real-World Examples

I analyzed my media library and found several high-resolution files that are not classified as 4K/UHD with the current logic. Here are actual examples:

2592x2160
2872x2156
2876x2160
2880x2160 (multiple files)
2960x2160 (multiple files)
2972x2160
3232x2152
3556x2156
3564x2156
3576x2156
3582x2160 (multiple files)
3584x2160

All these files have vertical resolutions at or very near 2160p, which is the vertical resolution standard for 4K/UHD content. However, they fall below the 3800px width threshold and thus aren't classified as 4K/UHD content.

Proposed Change

PR #13332 adds height-based detection (≥2100px) as an alternative criterion for 4K/UHD classification. This would properly categorize these high-resolution files while maintaining the existing width-based detection.

Concerns

• Commercial cinema and TV standards define 4K specifically by horizontal resolution (~4000 pixels)
• Different standards have specific definitions:
  • DCI 4K: 4096×2160, 3996×2160, or 4096×1716
  • SMPTE/ITU-R UHD: 3840×2160
• Streaming platforms use more flexible definitions (e.g., YouTube's "4K UHD" includes 2160p content)
• This change would shift us from an industry-standard horizontal definition to a more vertical-based approach

Questions for Discussion

Should Jellyfin strictly follow commercial standards, or adapt its classification to better match real-world content variations?

[Shadowghost]

IMHO we should use a more versatile approach. I'm all for using standards but in this case we miss any content where stuff like black bars were removed before (re)encoding because they take away from the height. From a user perspective that's still a 4k/UHD (or to be more correct 2160p) media.

[mikesulsenti]

An example of that resolution type is a 4K movie I re-encoded and clipped the black bars:
3840 × 1608

And similarly, 1080p movie files would have their own clipped black bars, often:
1920 × 804

Some other outliers may be more less

[MrPeteypoo]

The terminology in the video space for resolutions can be very confusing at times. It might be helpful to stop using the term "4K" and use the more general "Ultra HD" or "UHD" term. Although UHD is very often synonymous with 4K I think it more accurately includes cases where a 3840x2160 movie is cropped to 21:9 by removing the black bars (becoming 3840x1608) or where you have a 4:3 movie with a resolution of 2880x2160. 2160p Isn't a good alternate because again with most movies being in 21:9 it isn't very accurate. I would classify UHD as being anything above FHD (either 1920 pixels wide or 1080 pixels tall) unless there is a desire to introduce QHD (either 2560 pixels wide or 1440 pixels tall).