[x265] [PATCH] Backed out changeset: fef63866bb60

[Pradeep Ramachandran]

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?


> --
> Vittorio
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