the ffmpeg-ffserver-dev.tcz extension I'd posted 2010/06/05 did contain the libswscale dev files and also had been compiled with --enable-shared.
The current extension does not contain the libswscale dev files and also has not been compiled with --enable-shared, hence the large size of the ffmpeg extensions.
It would seem to make sense to compile the ffmpeg extensions with --enable-shared and with deps on libav*, libswscale, which are used by several extensions that do not require the full ffmpeg binary?