Just another quick update. I converted another avi with an ac3 audio stream. In WinFF, I used the preset with “-async 2” at the end. The ffmpeg log was 100% clean. The result is perfect sound (no glitches, perfectly synchonized with video). I guess this means a couple of things:
ac3 audio streams can convert just as well as cbr mp3 streams with this procedure.
Some avi’s are “dirty” and do not convert as cleanly as others. In this case, unless you take several steps to doctor the audio stream and ensure proper synchronization, the “quick procedure” can produce a very good result with minor audio glitches.