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

[Reimar Döffinger]

On 8 June 2020 20:04:42 CEST, Kevan Hashemi <hashemi at opensourceinstruments.com> wrote:
>Dear Reimar,
>
>Thanks for your attention.
>
>> I don't know what you're trying, but mostly I'd say that the result
>wouldn't make any sense.
>
>I expect that I'm using the word "scaling" wrong. When the user changes
>the size of the window, the video display changes size also. I don't
>know what that's called. Maybe it's "zoom", because that's the command
>I use to have the same effect. I'd like to be able to tell the slave to
>change the value of "zoom".

Well, my suggestion would be to just change the size of MPlayer's window (I believe most windowing systems allow you to manipulate windows of a different program) if that's what you want to happen.
Assuming you don't want to go for embedding via the - wid option.
If you need to use -zoom that's not an ideal setup for MPlayer because it means you are using a really outdated method to display the video. It almost certainly lacks a few other nice features like nicely blended subtitles etc.
Assuming it does not exist, a slave command to change the windows size is not unreasonable either, but it should be a video output command, not a video filter command.
Same way as you should use -geometry if you want the window to start up at a certain size, not -vf scale. 

>> If you want the window a different size you can just make the window
>a different size
>
>I can't as the process sending commands into the slave MPlayer. So far
>as I know, only the user of my program can change the window size.

See my answer above: it's at least worth checking if you really can't.
But I will admit that even if you can, it might not be very convenient to do that way.

>> Similar for expand.
>
>As above: I doubt I know what you mean by "expand".

Someone mentioned -vf expand.
The only use-case for that I could think of should be possible to replace simply by panscan, for which I'm quite sure there are slave commands.