FFmpeg commit r11071 removed the static ByteIOContext from AVFormatContext
and replaced it with a dynamic one.
Thus muxer_lavf.c needs to be modified to reflect the change.
git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@25135 b3059339-0415-0410-9bf9-f77b7e298cf2