require 'ezfile'

pwd = Dir.pwd

Ezfile.files("*") # default is "*" 
.group_by{|fname| Ezfile.mainname}
.select{|mname, fs| fs.any{|f| Ezfile.extname(f) == ".ass"}}
.each do |fname, fs|
    ass = File.combine(pwd, fname +".ass")
    mp4 = File.combine(pwd, fname +".mp4")
    outf = fname+".done.mp4"
    system %Q(ffmpeg -i #{mp4.inspect} -vf subtitles=#{ass.inspect} -c:v h264_nvenc "./out/#{outf}")
end

Ezfile.help

<<-EOF
              require FileUtils and Dir, File.
          methods:
           MOVE :
          ::move_file file_path target_dir, mkdir: false
              move file to target directory
              ! if directory is non-exist,
              throw an error.
          ::move_file  file_path, target_dir
              if non-exist, mkdir
           QUERY :   its syntax like Explorer Search
          ::file_list  target_dir = "*"     alias ::files
          ::dir_list  target_dir = "*"      alias ::dirs
              show list of files/directories, of target_dir.
              ! using Dir.glob(target_dir)
          ::glob query
              the same as Dir.glob(query)

           RENAME :
          ::rebasename_file src_file_path, new_basename
              it change a file's basename, and ensure never move it or change its parent node.

           DELETE :
            ::ensure_permanently_delete_file target_file     alias ::files
            ::ensure_permanently_delete_directory_and_its_descendant target_dir     alias ::files
EOF