Adding visual audio level monitors

With the ability to overlay images to the video stream tackled the next task was to analyse the audio and overlay VU meters to allow us to see how noisy the little tyke is without having to actually listen to him (it is a him btw, he popped out on the 22nd June).

The camera uses the linux open sound system (OSS), which has been replaced by ALSA in linux 2.5 and above and isn't particulary nice to work with. The camera streaming server (camserv) , for which there is no source code, opens the audio-in device on startup and as it can only be opened once (and without it being available camserv refuses to work) I had to look at other avenues to get the audio.

Fortunately, camserv actually offers the audio out in a mangled stream which can be found at http://[cam-ip]/cgi/audio/audio.cgi - this stream provides chunks of audio data in 16bit PCM stream at what appears to be about 8KHz (although the frequency is only being guessed at). The stream isn't presented in a friendly format (i.e. browsers don't recognise it and simply try and download it as a series of files) but it is quite easy to write a bit of code to connect to the port and analyse the audio.

I put together some code to connect to the stream and display the current, peak and average volume overlayed on the video stream. It uses some of the same code used for the text display on the previous entry and seems to run around 1/4 sec behind the actual audio (this is due to the audio being streamed locally, analysed and then overlayed onto the video).

I have included the source code and a compiled version here, and below is a short video of it being streamed to an iPad:




And here it is on Apple TV2 via XBMC:



To use the code on your camera it does need to authenticate to the local camera web server; it defaults to username:admin pasword:admin as do the cameras out of the box, if you are using your own username and password (and I strongly suggest you do) you will need to specify the base64 encode of the username and password on the command line via -a . There are a number of websites which can do is encode so I haven't included this in the code; the format needs to be a hash of the username:password (e.g. 'admin:admin' which has a hash of 'YWRtaW46YWRtaW4=')