Why can not convert BBC iPlayer MP4 file to remove the protection?

As we know, there are two file formats from BBC iPlayer, one is WMV format and the other is MP4 format. When converting DRM files, the program records the original files when they are playing and save the recordings to unprotected digital formats. The MP4 video can only be played on BBC iPlayer, but not the program. That is why the MP4 files from BBC iPlayer can not be converted. You can download BBC WMV file to convert. If not, you can use the recording function: