With HDR video becoming more prevalent in home media, the P2P community has developed software to edit these new formats. Unfortunately, since these tools are reverse-engineered, they don't always produce correct results. A common use case for these tools is adding dynamic HDR metadata from one source (e.g. a streaming service) to an otherwise static HDR source (e.g. a UHD Blu-ray Disc), see our HDR Format wiki for more info. Our goal is to maintain a problem-free viewing experience for our members. As such, following extensive testing and careful consideration by staff and internals, we have concluded that hybrid releases with dynamic HDR metadata from a second source are subject to the following requirements. This change will only affect users uploading dynamic HDR content.

BLU prohibits all hybrid releases that import HDR10+ metadata from a second source using the so-called "hdr10plus_tool". Based on our extensive testing of this reverse-engineered software, we have concluded that the results it produces are invalid.
In some cases, hdr10plus_tool modified and corrupted the original HDR10+ metadata.
In one of our tests, 400 scenes were missing from the JSON file that the incorrectly reversed tool claims to have parsed. This was verified using multiple OEM HDR10+ tools. Moreover, a considerable number of scenes were pointing to the wrong frames.
Such corruption produces wrong imagery, introduces blunders such as flickering, and causes devices' HDR10+ modes to sporadically engage/disengage during playback.
Such releases are permitted if (i) the metadata injection was performed using official HDR10+ authoring software and (ii) the uploader can reasonably prove that the service masters of the source and target video were the same.
In order to comply with point 2 (ii), the minimum requirement is that the uploader provide at least three evenly distributed pairs of images comparing identical frames of the static HDR versions of the web and Blu-ray sources.
Dolby Vision (DV)

Derived Profile 8, i.e. "Profile 5 (P5) → Profile 8 (P8)" conversions, using the reverse-engineered dovi_tool, are allowed as standard hybrid releases subject to the following:
Only valid conversions are allowed. This means:
The releaser/uploader must reasonably demonstrate (see point 1.3) that the HDR service masters of the web and UHD Blu-ray sources would have shared the same properties. This includes colour, tone and content aspect ratio in all scenes, including studio logos.
The P8 conversion must not originate from HDR10+ metadata or any other type of grading system, such as MadVR. Such conversions produce neither accurate nor similar results to an official DV colour grade.
In order to comply with point 1, the minimum requirement is that the uploader provide at least three evenly distributed pairs of images comparing identical frames of the static HDR versions of the web and Blu-ray sources.
Original WEB-DLs with native P5 may co-exist with a hybrid release consisting of a converted P8 profile which provides a fallback to standard HDR10. The original P5 (DV only) WEB-DLs are still welcome and encouraged because they use a more appropriate colour space and produce higher quality results at the same bitrate.
For now, hybrid remuxes consisting of web-sourced converted P8 metadata shall co-exist with a Blu-ray remux or WEB-DL containing the original video stream.
All derived DV uploads must have a note at the top of the description with the following text in addition to any required frame comparisons (remove the space before code):
[ code]This release contains a derived Dolby Vision profile 8 layer. Comparisons between HDR masters: [link or spoiler with comps][/code]
A remux consisting of Blu-ray sourced DV (P7) trumps one consisting of web sourced (P8) metadata.
A final word

We have based our decisions on extensive testing and comparisons of movies that already have native DV on both their Blu-ray and web options.

From a theoretical perspective, we can confirm, for example, that converted P5 → P8 (web) and P7 → P8 (Blu-ray) profiles of the same movie shared similar values, with the P7 source sometimes having additional parameters and options. Otherwise, they shared the same metadata where relevant and even hash matched in some scenes.

From a practical perspective, users may wish to note that web-based DV profiles are primarily static layers. They may or may not improve your viewing experience over standard HDR10. They certainly will not do so nearly as well as the more sophisticated HDR10+ Profile B or Blu-ray DV grade. For example, in our blind abx tests, it was evident that the more dynamic profiles were considerably more capable than P5 → P8 hybrids at producing specular highlights and dark area detail simultaneously.