I personally would not prefer to add the full FFMPEG SDK, as it increases the app size exponentially, however using Arthenica's FFMPEG-KIT seems the easiest way to get FFMPEG into a project

implementation "com.arthenica:ffmpeg-kit-min-gpl:5.1.LTS"

This new FFMPEG-KIT not only has a reduction in size, but the commands also execute quicker and have better async support and much easier implementation.

To use you just have to import

import com.arthenica.ffmpegkit.FFmpegKit
import com.arthenica.ffmpegkit.ReturnCode

and then :

FFmpegKit.executeAsync(cmdString , {
    when {
        ReturnCode.isSuccess(it.returnCode) -> {
            println("FFMPEG SUCCESS :${it.state.name}")
        }

        ReturnCode.isCancel(it.returnCode) -> {
            println("FFMPEG CANCELLED :${it.returnCode}")
        }

        it.returnCode.isValueError -> {
            println("FFMPEG ERROR :${it.logs.last()}")
        }
    }
} , {
    println("FFMEPG LOG :${it.message}")
} , {
    println("FFMEPG STATS :${it.speed}")
})

here cmdString, is a string of commands, your commands should work but the only issue I ran into was that I had to use -y -i instead of -f which seemed to run the commands.

I have used belowed version of ffmpeg that increase the conversion speed and works in all android version Displayed in documentation...

https://github.com/tanersener/mobile-ffmpeg

hope this will work for you..!!!