This program allows you to record the output of any standard OSS program (one that uses /dev/dsp for sound) without having to modify or recompile the program. It uses the same idea as the esddsp wrapper from the Enlightened Sound Daemon (in fact, vsound is based on esddsp). That is, it preloads a library that intercepts calls to open /dev/dsp, and instead returns a handle to a normal file. It also intercepts ioctl’s on that file handle and logs them, to help convert the audio data from its raw form. Vsound then uses sox to convert the raw data to the desired file format.
The upshoot of this is that instead of playing sound to the sound card in your computer, the data is recorded to a file. This is similar to if you connected a loopback cable to the line in and line out jacks on your sound card, but no DA or AD conversions take place, so quality is not lost.
One use of vsound is to help convert real audio files to some other format. Since the real audio format is proprietary, and all we have is a player, we can use the vsound to create a wave file like so:
vsound -t -f /data/dvdburn/LL2/s2.wav realplay rtsp://220.127.116.11/ailab/mit-ll2-s2-09nov02-80k.rm