PHP wave form image generation

I would like a function that will read in a 16 or 24 bit stereo wav file (44100khz), between 3 and 10 minutes long, and generate a mono waveform image similar to those used on [login to view URL] or zippyshare.com. The image size should be flexible, but will be approximately 600 x 80 pixels. I've done some reading on this and apparently the image generation can take a long time to process, therefore the function should create the image as quickly as possible, and there it will be necessary to investigate ways to skip values within the wave file to read approximate values - there are a number of articles on the web explaining this. In addition, it would be very useful to obtain a value from the file representing maximum loudness - the basic idea being to tell if the wave has been mastered to obtain optimum volume or [login to view URL] should be calculated using averages over 10 seconds section of the file i.e. find the rms of the loudest 10 second section of the file. I'm not an expert on this stuff but I know this should be possible with a bit of investigation. Please message me if you have any further questions. Thanks.