How to extract bandwidth usage from tcpdump capture file?

Hi, I've got a tcpdump capture file and am looking for a utility that
will read the file and output either the average bandwidth over an
interval of time or the number of bytes in that interval of time.
tcptrace -xslice is almost perfect--the only problem is that it only
counts TCP packets. I need the data for all packets in the trace.

For those who aren't familiar with it, the output from tcptrace
-xslice looks like:

date                segs    bytes  rexsegs rexbytes      new   active
--------------- -------- -------- -------- -------- -------- --------
15:03:26.707663     1790   241521        8     4457       21       21
15:03:41.707663     2875   799428        5     7281       32       39
15:03:56.707663     2590   688734       19    11988       17       34
15:04:11.707663     2856  1063850       16    18228       44       52
15:04:26.707663     2188   550299        8     7696        6       39

I only need the "date" and "bytes" columns.
-- 
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