+ /** Start a progressive write to this asset.
+ * @param overwrite true to overwrite an existing MXF file; in this mode, writing can be resumed to a partially-written MXF; false if the
+ * MXF file does not exist.
+ * @param metadata MXF metadata to use.
+ */
+ virtual boost::shared_ptr<PictureAssetWriter> start_write (bool overwrite, bool interop, MXFMetadata const & metadata = MXFMetadata ()) = 0;