Original commit message from CVS:
* ext/ffmpeg/gstffmpegcodecmap.c:
(gst_ffmpeg_formatid_get_codecids), (gst_ffmpeg_caps_to_codecid):
Add mmf to _get_codecids, so we can use the mmf muxer.
Use "audio/x-adpcm" rather than the dubious looking "x-adpcm" as our
caps type for the adpcm variants.

* ext/ffmpeg/gstffmpegmux.c: (gst_ffmpegmux_base_init):
Allow muxers that allow either only audio or only video, needed for
mmf (audio only).