Originally Posted by nathan_h
You are right. There are versions of DV in places other than UHD BR that do not require HDR10 base layer. However, Apple (the subject of this thread) has chosen DV profile 5, which includes a generic HDR layer plus DV metadata on top.
I assume your interpretation on DV Profile is based on this PDF: https://www.dolby.com/us/en/technolo...2-9-170601.pdf
I read posts before discussing Profile 5 and what it means and they seemed to say that includes a generic HDR layer but when I looked at this PDF I can't reach the same conclusion. Please feel free to correct my interpretations.
For DV Profile 5, relevant details are
BL signal cross-compatibility ID: 0
Bitstream Profile name: dvhe.stn
VUI: 2, 2, 2, 1 [Probably Irrelevant - EOTF, color primaries, matrix, and range respectively.]
Now to break this down, BL signal cross-compatibility ID is 0, which means "none, but ITP and IPTc4 color spaces are supported". I am not entirely sure what they are saying with this ID # and maybe this is the key point here but
An identification number that can be used as a shorthand for a particular form of a base-layer sub-stream that can be decoded to a signal compliant with a particular set of standards
I interpret this as the ability to decode to a different standard like HDR10, SDR or Blu-ray HDR etc. Note that the ID# is not 1, which means CTA HDR10 and as far as I am concerned, since the BL signal cross-compatibility ID is 0 and not 1, there is no HDR layer.
The Bitstream profile name dvhe.stn can be broken down as such
he = HEVC
[number_of_layers] s = Dolby Vision stream has a single layer (not relevant AFAIK
) [Though in this paper https://www.dolby.com/us/en/technolo...ormat-v1.1.pdf
it mentions that a Single layer is not SDR-compliant, which is irrelevant but interesting I suppose...]
[bit_depth] t = bit depth of 10
[cross-compatibility] n = the Dolby Vision stream is not compatible with other standards for dynamic range, but uses Dolby Vision ITP or IPTc4 color space.
The last part is the most important and this is why I think Profile 5 does not have a base HDR layer. See the "cross-compatibility" value is not "h". If it was, the PDF says
h indicates that the Dolby Vision stream is compatible with CTA HDR10, as defined by the static metadata. CTA HDR10 is a 10-bit signal that leverages ST.2084, ST.2086, CTA-861- G, 4:2:0, and a BT.2020 container with P3 color primaries.
Thus, I don't think that there is a base HDR layer based on the Profile 5 spec.
Now, iTunes may still deliver a HDR layer but as far as this Profile spec is concerned, it probably doesn't. What does the Dev info panel for the aTV 4K show for DV movie content on a HDR10 TV? Or is that muddled by the aTV's always HDR mode?
Curious to hear your thoughts!
PS: On a side note, The other cross-compability values are interesting, e.g., "r" = backward compatible and DV stream can be decoded to SDR signal and "b" indicates that the Dolby Vision stream is Blu-ray Disc backward compatible (Ultra HD Blu-ray Disc high dynamic range).