[vlc-devel] [PATCH] vout: create/release the decoder device when the window is enabled/disabled

[Alexandre Janniaux]

Hi,

Wasn't the workshop only about window / decoder, and video context the
previous name of what become decoder_device ?

It might become confusion with Steve's video context(s) definition.

What would create the (only?) video context and what do you want the video
context to bring to the filter pipeline in a real world case ?

Regards,
--
Alexandre Janniaux
Videolabs

On Thu, Sep 19, 2019 at 03:06:20PM +0300, Rémi Denis-Courmont wrote:
> No. The name is correct. That's thewhole point of distinguish between decoder device and video context.
>
> The decoder device abstracts the video decoding DSP, and shields the decoder abstraction from depending on windowing systems (so that headless decoding is possible).
>
> The video context provides abstracts the GPU for video processing purpose - filter, conversion, blend and render. The video context is guaranteed to have a window underneath it, since rendering may depend on the intended display controller.
>
> Le 19 septembre 2019 10:19:13 GMT+03:00, Steve Lhomme <robux4 at ycbcr.xyz> a écrit :
> >On 2019-09-19 8:40, Rémi Denis-Courmont wrote:
> >> It's called "decoder device" because it's for the decoder.
> >
> >The name itself is not correct. As explained, it is also used by
> >filters
> >to create video context from scratch (that will output pictures
> >compatible with the "decoder device" used by the display module). We
> >could call it "output device" or even "output adapter" since it seems
> >to
> >always be tied to a display adapter.
> >
> >In the case of transcoding it's actually the device used by the
> >encoder,
> >that the decoder needs to try to match.
> >
> >As Alexandre reminded, it's mostly a hint for the decoder (and filters)
> >
> >to match the output. So we could also call it "device hint".
> >
> >> And the decoder device does not have to come from a window. That's
> >not how it's going to work for transcoding.
> >
> >It doesn't have to in most cases. But for devices like VAAPI it needs
> >to
> >know the type and ID of the window so the decoder can actually be used
> >(not sure if there are encoders for VAAPI and if they can use a dummy
> >VADisplay value). See the Open() of the VAAPI decoder device [1]. No
> >window => no "decoder device". No "decoder device" => no decoder.
> >
> >We actually designed the "decoder device" during the workshop because
> >of
> >that. I did not originally go that way since on Windows I never need to
> >
> >know the window (and in fact I can't know the adapter from the HWND).
> >
> >[1]
> >https://code.videolan.org/videolan/vlc/blob/master/modules/hw/vaapi/decoder_device.c#L223
> >
> >> Le 19 septembre 2019 09:30:30 GMT+03:00, Steve Lhomme
> ><robux4 at ycbcr.xyz> a écrit :
> >>> On 2019-09-19 8:11, Steve Lhomme wrote:
> >>>> On 2019-09-18 18:16, Rémi Denis-Courmont wrote:
> >>>>> Le keskiviikkona 18. syyskuuta 2019, 17.13.18 EEST Steve Lhomme a
> >>> écrit :
> >>>>>> The decoder device ("dec-dev") should be tied to the lifecyle of
> >>> the
> >>>>>> window.
> >>>>>
> >>>>> Well, no. It's tied to an enabled window, which is longer than a
> >>> vout,
> >>>>> but
> >>>>> shorter than a window.
> >>>>
> >>>> I can change it to:
> >>>> The decoder device ("dec-dev") should be tied to the lifecyle of an
> >>>> enabled window.
> >>>>
> >>>>> And AFAIK, the vout should not know about the decoder or decoder
> >>>>> device at
> >>>>> all. It should use the video context only.
> >>>>
> >>>> And how do you plan to convey this decoder device instance to the
> >>>> decoder/filters without going through the vout ?
> >>>
> >>> For the record, the decoder device is created with a vout_window_t,
> >>> because in some cases (VAAPI for example) it needs to know about
> >which
> >>> window is used. This vout_window_t is created and stored by the
> >vout.
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> >>
> >> --
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> >excuser ma brièveté.
> >>
> >>
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