Dumping raw TS

Not strictly a tvheadend question but it's related.

I'd like to attach a raw dump of a MUX to a ticket I've created but I can't figure out how to do it.

I've tried using dvbsnoop but it doesn't seem to be able to dump a TS if tvh has the tuner locked for use. I have also tried using dvbtune but if I run that in monitor (-m) mode I get the same "device or resource busy" message in dvbsnoop. If I don't use the -m option, the .ts file is 0 bytes.