Get YouTube audio stream on-the-fly

I am trying to get an audio stream (in mp3 format with fixed quality) from a YouTube video in PHP. Notice that I cannot use FFMPEG and also i do not want to save the mp3 on my server, but I need only the audio stream (on the fly use). Do you have any code or script? I have used many, but the half needs FFMPEG and the other saves the mp3 file in the server. My plan is to hit on the browser: ``` http://host.com/process.php?url=<youtubeurl> ``` and get the audio stream in the page in variable that creating every time ``` &stream = ......; ```