C:\Program Files\Wireshark>tshark.exe -i 4 -x -t ad -R 
  "myprotodissector.something==528" -b filesize:5000 -w 
C:\Traffic.pcap
  
  This is what the manual says:
  
  
  -R <read 
  (display) filter>
  
  Cause the specified filter (which uses the syntax of read/display filters, 
  rather than that of capture filters) to be applied before printing a decoded 
  form of packets or writing packets to a file; packets not matching the filter 
  are discarded rather than being printed or written.
  
 
  
  A 
  capture or read filter can either be specified with 
  the -f or -R option, 
  respectively, in which case the entire filter _expression_ must be specified as 
  a single argument (which means that if it contains spaces, it must be quoted), 
  or can be specified with command-line arguments after the option arguments, in 
  which case all the arguments after the filter arguments are treated as a 
  filter _expression_. Capture filters are supported only when doing a live 
  capture; 
  read filters are supported when doing a live capture and when reading a 
  capture file, but 
  require TShark to do more work when filtering, so you might be more likely to 
  lose packets under heavy load if you're using a read filter. If the filter is 
  specified with command-line arguments after the option arguments, it's a 
  capture filter if a capture is being done (i.e., if 
  no -r option was specified) and a read filter if a 
  capture file is being read (i.e., if a -r option 
  was specified).