Is there a freeware Windows/Linux GUI packet replay tool that has the advanced features of tcpreplay (http://tcpreplay.synfin.net/) or bittwist (http://bittwist.sourceforge.net)? I'm particularly interested in the following features:

1. Open pcap files for editing and injecting into arbitrary network
2. Change source and destination addresses/ports of UDP packets
3. Change packet timing (with millisecond resolution)
4. Edit packet contents, including modifying its length
5. Has graphical front end for Windows or Linux (or Mac OS X)

I've scanned a couple lists of potential tools (here and here), but nothing really fits my requirements. The closest tool might be Ostinato (http://code.google.com/p/ostinato/), but it doesn't appear to open packet capture files. Thanks for any help!