[MPlayer-users] No vf_ commands for -slave?

[Reimar Döffinger]

On 8 June 2020 17:52:53 CEST, Kevan Hashemi <hashemi at opensourceinstruments.com> wrote:
>
>MPlayer Experts: is there anything to stop us from adding a command to
>the slave mode to do scaling?

I don't know what you're trying, but mostly I'd say that the result wouldn't make any sense.
Scaling up would have the only effect of making things go really slow, scaling down would have the only effect of making the video blurry.
If you want the window a different size you can just make the window a different size, scaling wouldn't even come in (at least not explicit scaling). 
Similar for expand. 
If you want borders, that's called panscan.
Or to put it real short: you're asking to make filters runtime configurable that should never be used at all in the first place (essentially, they exist to handle corner-cases that should only exist on systems particularly unsuitable for MPlayer).