Bob,
There was a post here or on QRZ recently asking for just that instant playback capability, e.g., missing part of a call sign. Good work on the video, and I subscribed to the channel. That is a great targeted application for the $5 Pi.
So far I've tried out my horrendously expensive ($8) USB sound gadget from Amazon only on the laptop. Should have got the sound card you did and got on a wait list for the Pi junior. I've got some work ahead of me in getting the fldigi Pi B+ going. I got a cheap composite video backup camera display to see if 4.3" diagonal will work for the field.
Ted, KX4OM