On Wed, Mar 13, 2019 at 11:49 AM Vittorio Giovara < [email protected]> wrote:
> > > On Wed, Mar 13, 2019 at 10:41 AM Pradeep Ramachandran < > [email protected]> wrote: > >> On Tue, Mar 12, 2019 at 10:21 PM Vittorio Giovara < >> [email protected]> wrote: >> >>> >>> >>> On Tue, Mar 12, 2019 at 12:11 PM Aruna Matheswaran < >>> [email protected]> wrote: >>> >>>> Thanks for the pointers, Vittorio. CTA-861.3-A specification states >>>> that if both MaxCLL and MaxFALL are signaled as 0, the rendering device >>>> shall interpret it as unknown. >>>> >>> >>> Thanks for your response, I am aware of this and it logically makes >>> sense. >>> >>> With this reference, x265 by default is signaling 0 for both MaxCLL and >>>> MaxFALL with the assumption that any logical implementation of the >>>> specification would ignore them. >>>> >>> >>> This part I don't understand. The possibility of avoiding sending this >>> SEI is just one if clause, what is the purpose of encoding an empty >>> message? Is it a requirement for some other specification? Does it serve a >>> private x265 use? Nothing wrong in either, but please have it documented >>> somewhere. >>> >>> The problem we see now is that your renderer interprets 0 content light >>>> levels as valid values and displays too dark or too bright pixels. Whereas >>>> a few other renderers don't accept NULL entries for content light levels >>>> and expect 0 content light level as a signal to disable/ignore their usage. >>>> >>> >>> Unfortunately though it is not *my* renderer, but it's the renderer of >>> some tvs and devices in the wild, over which I have no control. >>> >>> Will introducing *an additional param flag to enable signaling of only >>>> mastering display metadata *fix your problem? With this, renderers >>>> which don't accept NULL content light level entries shall use the default 0 >>>> signaling. On the other hand, renderers which treat 0 content light level >>>> as valid entries shall disable signaling them via the additional flag. >>>> Please share your thoughts on this suggestion. >>>> >>> >>> This would kind of work but I do not believe it's a proper solution. At >>> most, the default behavior should be the one of least expected surprise: if >>> message is empty just don't encode it. Then if a sensible usecase really >>> exists, there should be an option to force encode light level even if >>> empty. However it's still unclear why you would need to that in the first >>> place, as trusting decoders to do the right thing is not very efficient and >>> leads to a catch-a-mole experience. >>> >> >> We have other users who've come back to us with the report that that >> unless maxCLL and maxFALL are signalled as (0,0), their decoder/renderer >> is decoding this as an invalid HDR10 stream. (My email earlier about >> non-HDR10 streams was incorrect; please ignore that.) Your use case is that >> your decoder interprets (0,0) as a valid value and renders the pixels >> incorrectly! As this SEI message is pass-through for the encoder, we just >> went back to the standard and did what we thought was the right >> interpretation of the standard, and that was to signal *all* HDR10 params >> when *any* HDR10 param was non-zero. And we had another request from a user >> asking for having the ability to always signal HDR10 SEIs even when they >> were zero and that is why we added the --hdr option. (In hind-sight, we >> should've called this --hdr10, but we will live with it for now.) Now, your >> use-case is that you want a sub-set of the HDR10 SEIs to be signaled and >> not the others. Maybe adding separate flags for force-signalling them >> separately is the best option here, but so many flags isn't a good thing! >> > > A couple of points here: > - it's not "my decoder", but decoders installed on *some* tvs and *some* > devices. I have no control over those devices and I can't even gather data > about which devices these are > - I am not using the --hdr(10) option from the command line interface, > this all comes from the API. While I can expect some kind of automatic when > using the CLI, the API itself should not "surprise-encode" messages that > weren't explicitly enabled (especially if empty > - hdr10 is mostly a commercial term, it's not a real "standard" per se but > a collection of specifications stitched together. There is no such thing as > "invalid hdr10 stream" because there is no conformance to adhere to: > decoders or renderers needs to apply whatever information is present in the > stream, to the best of their support. Some perform better some perform worse > - I disagree with limiting the number of "so many flags": this is a video > encoder which is not a simple thing to begin with, so exposing more knobs > to allow more in-tune configuration to "expert" users is actually > appreciated (to a limit) > - I agree --hdr should have been called --hdr10 but it's never too late to > add/deprecate that, especially when major bumps are around ;) > -- > Vittorio > ping I suppose -- Vittorio
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