Writes the current buffer contents to the given stream.
See also File Formats.
(send a-wx:media-edit write-to-file streamstartend)->boolean stream : wx:media-stream-out% object start : small integer end = -1 : small integer
If start and end are -1, then the entire contents
are written to the stream. If start is not -1, then the
contents are written from start until the end of the buffer.