-x '1 2 3' -y 4 5

##</code><code>##

--extra-ffmpeg-param='-x '\''1 2 3'\'' -y 4 5'

##</code><code>##

--extra-ffmpeg-param='-x "1 2 3" -y 4 5'

##</code><code>##

# to_shell_lit() - Creates a shell literal
# Usage:  printf '%s\n' "$( to_shell_lit "..." "..." "..." )"
to_shell_lit() {
    local prefix=''
    local p
    for p in "$@" ; do
        printf "$prefix"\'
        printf %s "$p" | sed "s/'/'\\\\''/g"
        printf \'
        prefix=' '
    done
}

--extra-ffmpeg-param="$( to_shell_lit -x "$x" )"

##</code><code>##

-X '-x 1 2 3' -X '-y 4'

##</code><code>##

-X "-x $x" -X '-y 4'

##</code><code>##

-X 'x=1 2 3' -X 'y=4'

##</code><code>##

-X "x=$x" -X 'y=4'