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

[Steve Lhomme]

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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