Since FFmpeg official documentation (libavcodec is part of ffmpeg) states that only these versions of H263 are supported:
H.263 / H.263-1996
H.263+ / H.263-1998 / H.263 version 2
I think it would be a fair shot to presume that H263++ isn't supported by libavcodec (the official docs don't include it). To be 100% sure, I'd check it traditional way - download libavcodec and try to use it with a sample H263++ video ;)
Since FFmpeg official documentation (libavcodec is part of ffmpeg) states that only these versions of H263 are supported:
I think it would be a fair shot to presume that H263++ isn't supported by libavcodec (the official docs don't include it). To be 100% sure, I'd check it traditional way - download libavcodec and try to use it with a sample H263++ video ;)
BTW - I think this question belongs to superuser.