"Way to capture sound card output as wav when playing mp4?"
It's not the solution i'd chose, but this should work http://www.highcriteria.com/main_productfr_tr_overview.htm
Some soundcards have an internal loopback that can map the output back into the input (ESI Waveterminal series springs to mind), might be an idea to check your soundcard doesnt support that before you procede...
It's not the solution i'd chose, but this should work http://www.highcriteria.com/main_productfr_tr_overview.htm
Some soundcards have an internal loopback that can map the output back into the input (ESI Waveterminal series springs to mind), might be an idea to check your soundcard doesnt support that before you procede...