Crash confirmed on Linux x64, it's falling over in intern/readfile.c - direct_link_scene() where it tries to set seq->strip->proxy->anim to NULL but proxy itself is NULL so it segfaults. Perhaps this file expects proxy data (do you have proxy data on disk OP, or is this someone else's file?) and this function cannot cope if it is not found?

Just for yuks I tried adding a check for proxy == NULL and cleared the SEQ_USE_PROXY bit of seq->flag if true, and it loads fine (though there is still something amiss as it crashes in an infinite loop in my strip-relative frame offset calculation routine, as per T49658).

Presumably this file is from some older version of Blender, and the conversion routines cannot cope with a combination of set SEQ_USE_PROXY bit and missing proxy data?

I saved the resulting file and it now opens with unmodified 2.78:

FWIW I've made a diff for the patch that stops it crashing.

Wow, thanks so much Olly. I might just be able to recover the stuff I couldn't from the backup.

It's my file. I don't know if it's using proxy data; I'm not sure what that is. I'm assuming you mean a proxy file instead of the original file, but it's meant to be a text effect strip so there's no data on the disk. How do I find out?

Also let me know if there's anything else you need.

TBH I didn't see anything specific to text strips in the debugger - it fails trying to load proxies on the following sequences:

frerf.948
frerf.001
frerf.016
frerf.mp4
frerf.077
power rangers 3..001
Scene.004
Scene.001
Scene
Scene.002

and many more but I'm bored of typing them here :o)

Nothing specific to text strips, perhaps it was just coincidence and the file got corrupted at the same time as you added the text strip?