Reads data from in to initialize for reading buffers from the stream. The return value is #t if the read succeeds, or #f otherwise. One or more buffers can be read from the stream by calling the buffer's read-from-file method. (The number of buffers to be read must be known by the application beforehand.) When all buffers are read, call wx:read-media-global-footer. Calls to wx:read-media-global-header and wx:read-media-global-footer must bracket any call to read-from-file, and only one stream at a time can be read using these methods or written using wx:write-media-global-header and wx:write-media-global-footer.