How can I cut a video to a certain length and add an intro video to it using ffmpeg-python?

I am doing this:

intro = ffmpeg.input(intro)
mainvid = ffmpeg.input(mainvid)

v1 = intro.video
a1 = intro.audio
v2 = mainvid.video
a2 = mainvid.audio

joined = ffmpeg.concat(v1, a1, v2, a2, v=1, a=1).node
v3 = joined[0]
a3 = joined[1]

(
    ffmpeg
    .output(
        v3,
        a3,
        'out.mkv',
        vcodec='libx265', )
    .run()
)

But I don’t know how to cut *mainvid to a certain length like 10 minutes before joining. I know ss will help, but I don’t know how to use it for only mainvid.

Solution

I managed to do it using:

        intro = ffmpeg.input(intro)
        mainvid = ffmpeg.input(mainvid, ss='00:00:00', t='00:10:00') 

        v1 = intro.video
        a1 = intro.audio
        v2 = mainvid.video
        a2 = mainvid.audio

        joined = ffmpeg.concat(v1, a1, v2, a2, v=1, a=1).node
        v3 = joined[0]
        a3 = joined[1]

        (
            ffmpeg
            .output(
                v3,
                a3,
                'out.mkv', 
                vcodec='libx265', )
            .run()
        )