- let DV muxer generate audioless DV streams. This might not be 100%
complaint with the SMPTE & IEC specs, but it seems harmless enough.
The way we "specify" that there's no audio is by simply leaving
audio DIFs filled with 0xff (I bet there's a way to mark this
properly in the system info section!).
Originally committed as revision 3526 to svn://svn.ffmpeg.org/ffmpeg/trunk