"Fly Me to the Moon", a pop standard song written by Bart Howard in 1954, originally titled "In Other Words".
Lyrics: Bart Howard
Poets often use many words
To say a simple thing
It takes thought and time and rhyme
To make a poem sing
With music and words I've been playing
For you I have written a song
To be sure that you know what I'm saying
I'll translate as I go along
Fly me to the moon
And let me play among the stars
Let me see what spring is like
On Jupiter and Mars
In other words, hold my hand
In other words, darling, kiss me
Fill my heart with song
And let me sing forevermore
You are all I long for
All I worship and adore
In other words, please be true
In other words, I love you
 With music and words I’ve been playing.
It’s an inverted sentence. We may rearrange it as:
I’ve been playing with the music and words.
The verb “play” in Present Perfect Continuous Tense indicates that writing music and lyrics have been continuous for a long time and proceed to now.
play with somebody/something
► to keep touching something or moving it
--Stop playing with the light switch!
►to consider an idea or possibility, but not always very seriously
--After university, I played with the idea of teaching English in China.
► to try doing something in different ways to decide what works best
--Play with the design onscreen, moving text and pictures until you get a pleasing arrangement.
play with words/language
►to use words in a clever or amusing way
 I’ll translate as I go along.
►I’ll explain impromptu.
If you do something as you go along, you do it without planning or preparing it.
Let’s listen to the song on Youtube.