[vlc-devel] [PATCH v2 17/18] video_output: restart display after filter change

[Steve Lhomme]

On 2020-11-24 16:31, Rémi Denis-Courmont wrote:
> This seems to have the exact same problem as previous version. It is very much
> intended that we try to adjust the display conversion chain to adjust to
> changes in the chroma or video format properties that are not allowed to
> change for te display lifetime.
> 
> This allows swapping one conversion filter for another without messing the
> display. Restarting the display should only be done as absolute last resort.

I agree. But this is not the job of the converter (be is in 
osys->converter of filter.chain_interactive) to *cancel* format changes 
done by a filter. Some simple examples:

* deinterlacer outputs half the frame size, a converter will artifically 
double back that frame size for now reason, when the display with better 
resizing algo (and using less resources) could do the same.

* adding a GPU filter to a CPU-based pipeline, it will force a GPU to 
CPU at the end of filter to match the CPU format that was originally 
given to the display, when in fact it could do a lot better with the GPU 
source.

* interlaced hevc outputs pictures at half the original height, adding a 
deinterlace will output the proper height, an artificially converter 
will get back to the wrong size, losing half the lines and losing in 
quality in the process

* there are more and more talk about upscaler in various forms. This is 
especially crucial when playing low resolution sources (SD) on high 
pixel screens (8K). A source pixel become 64 pixels showing just ugly 
blocks of pixels. Upscaler make the estimation of each (8K) pixel better 
which smoother looking output. If we add such filters in VLC the whole 
point will be lost as we will turn an SD source to 8K and then to SD 
because the display was originally created like that.

> -1
> 
> -- 
> Rémi Denis-Courmont
> 
> 
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