[vlc-devel] [PATCH v1 07/33] filter: allow using filters with a sink callback to filter into a single picture

[Rémi Denis-Courmont]

Le lauantaina 26. syyskuuta 2020, 9.06.28 EEST Steve Lhomme a écrit :
> On 2020-09-25 17:27, Rémi Denis-Courmont wrote:
> > Hi,
> > 
> > That API is fundamentally incompatible with asynchronous use as the
> > filter would have no sink to output to outside the callback.
> 
> Filter users that use filter_FilterSingle() are indeed incompatible with
> an asynchronous system.

Not really. You can trivially convert a synchronous filter into an asynchronous 
filter by just calling the output callback on return. It can even be done in 
the owner side so that filters don't need to be modified one by one.

That's what we do for synchronous decoders.

> > That's why decoders get an owner callback for this purpose instead.
> 
> This does not change anything.

It changes everything. The owner callback is available at all times from open 
to close. The sink is only available during the filter call.

> > While I don't expect that asynchronous filters will work quiet yet, I
> > don't want to revector into an API that gets us further from the goal.
> 
> Sinks are actually a big step towards asynchronous use.

It's more like a big backward. It adds a new parameter and a new object that 
need to be replaced anyway for asynchronous, into something that will be 
exactly or very much like an owner callback down the line.

> The owner pattern is too centralized for that and would need to manage each
> step of the pipeline, maybe with a state machine or something.

I disagree and in any case the owner callback system is what was agreed to 
implement at multiple workshops already.

-- 
Реми Дёни-Курмон
http://www.remlab.net/