[vlc-devel] [PATCH 12/14] filter_chain: add a default implementation for the video_allocator

[Steve Lhomme]

On 2019-07-31 8:37, Steve Lhomme wrote:
> On 2019-07-30 18:52, Rémi Denis-Courmont wrote:
>> Le tiistaina 30. heinäkuuta 2019, 9.57.24 EEST Steve Lhomme a écrit :
>>>> If all GPU filters are using the video context, it means that you can't
>>>> have
>>> All filters have a video context, even if it's a "CPU" video context. A
>>> NULL video context will not be allowed. It wouldn't make sense, just
>>> like an empty video format doesn't make sense. It's also the best
>>> candidate to carry the decoder device along the whole filter chain (see
>>> previous answer).
>>
>> Sure it makes sense. Regular RAM has no reason to have a video 
>> context, except
>> maybe for convenience.
> 
> Except you can't tell if NULL means it's a CPU video context or it's 
> simply missing because the code couldn't create it in the first place.

We also need to carry over the original decoder device. It will be 
needed to adapt the last filter to the display. So we might as well put 
it in video contexts that which we already push downstream.

>>> Yes, at the very least the last filter in a chain must get pictures from
>>> the outside, not create its own.
>>
>> I completely disagree, and that's not how push model was designed.
>>
>> Push model means filters and converters allocate their *output* 
>> picture, just
>> like decoders do. Nothing else makes sense - the downstream has to 
>> handle the
>> case that there are no filters and the decoders pushes its pictures, 
>> so it
>> might as well do the same with filters.
> 
> And by what magic do you think it can accept any video format+context 
> it's given ? By using filters which will have to adapt for both the 
> input and the output format+context. And there are plenty of vout that 
> won't accept pictures they did not allocate. So the last filter will 
> have to handle the pictures from the outside/downstream (which is what 
> they do now).
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