Shoutbox

I think max. number was 1100 chars. Let's consider it as that.

You may use a for loop. Or even two.
Make a for loop that will add the text (in this case file paths) to the message, and another for adding those messages to another array which contains the mesages to be sent.
Let sendstr be the message going to be sent.

More detailed step by step:
Make array of song names (you did this one)
Make another array which will hold the strings to be sent.
Make an empty string
Make a loop that will;
Check if the string + next item on the first array (the one with songs names) exceeds 1100 chars, if doesn't exceed, add the text (don't also forget to add line breaks etc.), if exceeds, put the string to the second array (messages to be sent/forget indexing, just use push method), empty the string, and continue the loop until the first array is empty.

Ok, now, read that sentence slowly

After this is easy, you'll just send the messages until the second array is empty, each item as one message.