Flash MX 2004.
bitmapItem.useImportedJPEGQuality
Property; a Boolean value that specifies whether to use the default imported JPEG quality (true) or not (false). Available only for JPEG compression.
The following code sets the useImportedJPEGQuality property of the first item in the library of the current document to true:
fl.getDocumentDOM().library.items[0].useImportedJPEGQuality = true;
alert(fl.getDocumentDOM().library.items[0].useImportedJPEGQuality);