I used to have problems with files produced by gtkrecordmydesktop back
in 2009 (for some reason, the frames in the files I recorded back then
don't play in a fluid manner), but I just tested now with a screencast
recorded at 1920x1200 30fps and it played 100% fine in pitivi.

yeah, it's gtkrecordmydesktop files. I've just switched off to using ffmpeg to do the screen and audio capture. seems like w/ the options I'm using the video is crisper.

I'd be curious to see the footage file you are using. That sounds like a
candidate for a bug report.

I'll have to see how the ffmpeg files work, maybe the source is the problem.

Well, technically, the .xptv files are xml that can be edited or parsed
by external tools :)

Want to document the fields for me? I'll write a php xml parser that will spit out a ffmepg processing file.
 
or if there was someone sufficiently motivated to
write a patch for this UI you're talking about, perhaps that would
work... but again, I'm still unsure why you would need such a UI if you
had good playback performance to begin with.

if the playback is 1-to-1 with what you render, then yes, you're right. If not, the tool I suggest would make minor redits a lot easier.