Recent discussion on the list led me to realize that libavformat was
unconditionally creating an audio stream for all SGI movie format
(version 2) files, even when no audio is present in the file.
A sample of a movie file with no audio can be found at
http://www.personalprojects.net/ffmpeg/silent.movie
Unpatched ffmpeg will report an audio stream even though no audio is
present. After the following patch no audio stream is reported.
SGI movie files with audio are slightly affected by the fact that the
audio stream is now allocated after the video stream, changing the order
they are listed in the output of ffprobe or ffmpeg. I don't think this
materially affects anything. All existing FATE tests pass.
Incidentally, the silent.movie sample above is at 25fps and can also be
used by anyone who wants to double-check the earlier patch 3c9ffbd009
that reads and sets the framerate. The sample file is only about 88 KB.
