Sorry if I'm just missing something, but would editcap itself do the job?
editcap <in.pkt> <out.pcapng>
should read your Wildpackets file and produce a pcapng file; add a "-F pcap" for pcap format instead.
Can't speak to performance, but I'd be surprised if editcap were significantly slower than libwiretap itself for a straight read and write - but I've been surprised before.
Now, if you were looking to use the API from another program, that's a different problem - but your email said 'on the command line', so figured it was worth mentioning.
Depending on what you're doing, Wireshark itself might be a fairly large dependency for your purposes, but it'd probably be a lot easier to manage than a bespoke package (depending on what your OS and configuration infrastructure looks like) - possibly as simple as just adding 'wireshark' to a manifest/recipe/etc.). If the size is critical, you could also play around with the build options in Wireshark to see if you can just build editcap and see what the end result looks like - but then you're back to packaging it yourself.
-Tim
