[x265] [PATCH] Backed out changeset: fef63866bb60

[Vittorio Giovara]

On Wed, May 29, 2019 at 12:10 AM Pradeep Ramachandran <
pradeep at multicorewareinc.com> wrote:

> On Mon, Apr 1, 2019 at 11:06 PM Vittorio Giovara <
> vittorio.giovara at gmail.com> wrote:
>
>>
>>
>> On Wed, Mar 13, 2019 at 11:49 AM Vittorio Giovara <
>> vittorio.giovara at gmail.com> wrote:
>>
>>>
>>>
>>> On Wed, Mar 13, 2019 at 10:41 AM Pradeep Ramachandran <
>>> pradeep at multicorewareinc.com> wrote:
>>>
>>>> On Tue, Mar 12, 2019 at 10:21 PM Vittorio Giovara <
>>>> vittorio.giovara at gmail.com> wrote:
>>>>
>>>>>
>>>>>
>>>>> On Tue, Mar 12, 2019 at 12:11 PM Aruna Matheswaran <
>>>>> aruna at multicorewareinc.com> 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
>>
>
> Changeset ccc7a3edd595 has a new cli that we've added to enable cll
> separately. Does that fix the problems that you're reporting?
>

The cli portion is not needed for my usecase as I'm an API user, but the
internal changes should indeed fix the problem.
Thank you
-- 
Vittorio
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