I'm not sure what particular features of H.263 spec is used in Flash. You probably could start from exploring IPP media sample which contain H.263 support in both encoding and decoding. Note, for the simplicity we do not provide support for many container formats, so I would not expect IPP H.263 decoder will recognize or generate swf file format (although I do not know tech details on that format). Video encoder application which is part of that sample will take raw YUV file on input and produce raw encoded video as output. So you will need some extra development to wrap that to suitable container format.
IPP was designed to provide small memory footprint, so when you link with IPP static libraries and use only several IPP functions your application size will not grow dramatically.