After updating to mpv.net v7.1.2 (libmpv 0.41), thumbnail generation in thumbfast.lua fails and the video shows a white overlay.

[htyxyt]

Description:
After updating to mpv.net v7.1.2 (libmpv 0.41), thumbnail generation in thumbfast.lua fails and the video shows a white overlay.

Problem:
The issue is caused by the subprocess function in thumbfast.lua:

function subprocess(args, async, callback)
    callback = callback or function() end

    if not pre_0_30_0 then
        if async then
            return mp.command_native_async({name = "subprocess", playback_only = true, args = args, env = "PATH="..os.getenv("PATH")}, callback)
        else
            return mp.command_native({name = "subprocess", playback_only = false, capture_stdout = true, args = args, env = "PATH="..os.getenv("PATH")})
        end
    else
        if async then
            return mp.utils.subprocess_detached({args = args}, callback)
        else
            return mp.utils.subprocess({args = args})
        end
    end
end

Notes:

• Reverting to the old version without env = "PATH=..." restores functionality.
• The env field seems to be incorrectly formatted for mpv.net 7.1.2 / libmpv 0.41.
• Other parts of the script remain unchanged.

function subprocess(args, async, callback)
    callback = callback or function() end

    if not pre_0_30_0 then
        if async then
            return mp.command_native_async({name = "subprocess", playback_only = true, args = args}, callback)
        else
            return mp.command_native({name = "subprocess", playback_only = false, capture_stdout = true, args = args})
        end
    else
        if async then
            return mp.utils.subprocess_detached({args = args}, callback)
        else
            return mp.utils.subprocess({args = args})
        end
    end
end

Environment:

• mpv.net v7.1.2 (2026-01-09)
• libmpv 0.41
• Windows 10 / 11

[Kulsgam]

It does not seem to work on network streams even with your fix. Even when network is set to true, it still shows a white background for me.

[tunaflsh]

I think I know what's the problem you have @Kulsgam . On network streams, the filename argument gets replaced with the edl:// string, which includes tokens, video descriptions etc. and it gets very long. Can't say if it's the same issue env is making.