Writes data to out to initialize for writing buffers to the stream. The return value is #t if the write succeeds, or #f otherwise. One or more buffers can be written to the stream by calling the buffer's write-to-file method. When all buffers are written, call wx:write-media-global-footer. Calls to wx:write-media-global-header and wx:write-media-global-footer must bracket any call to write-to-file, and only one stream at a time can be written using these methods or read using wx:read-media-global-header and wx:read-media-global-footer.
See also section 
.