[vlc-devel] [PATCH] core: add a callback to init/release data for picture pool of opaque formats

[Rémi Denis-Courmont]

Le lundi 20 avril 2015, 17:22:07 Steve Lhomme a écrit :
> > So I don't see how non-serial data in video_format_t (or alongside it) can
> > ever work. FWIW, that issue was already brought up to solve a completely
> > different problem - multiple video output windows.
> > 
> > To take a simple and concrete example, how do you compare the video
> > formats
> > when there is an opaque pointer inside? Pointer comparison only works if
> > you know that the two pointed objects were concurrent in memory, such
> > that they cannot be two distinct objects with the same address.
> 
> There's one case where the code above may not work. If the old
> decoder_pool_setup_sys_t is freed, a new one is reallocated in the
> exact same place. Then it wouldn't work.

That is the point: Do not put non-serial(izable) data, such as opaque 
pointers, into or alongside format structures. It is not safe.

> I'm open to solutions to solve this.

Well, I can only repeat what I already wrote:

The *proper* solution is to pull any resources you need. Currently it can be 
done with the picture_sys_t, if the chroma is custom *and* if there are no 
video filters in the chain. Ideally though, there could add a function for the 
decoder to retrieve the hardware context from the video output after updating 
the output format but without pulling any specific picture.

Other than that, you have the kludges used by the preexisting opaque formats, 
involving the decoder writing into the picture_t context, the picture_sys_t 
and/or global variables.

-- 
Rémi Denis-Courmont
http://www.remlab.net/