Now that does explain the jerking in the images, presumably it is the extra frames and effectively they are changing the order from [a][b][c] to something like [a][b][b][b][c][c] causing the skipping effect.
I presume Brian that this sort of source layout is what you would consider to be a strange variable framerate - or is this some kind of special case in the respect of how it’s frame rate is handled that Shotcut might eventually be able to handle?
If it won’t handle it - it’s not a huge issue as I can use avidemux if required on those files - but it would be nice if it could handle it.
Cheers - and thanks for the personal investigation into this oddity.
I just exported a video at 60p and it jerked in Windows Viewer but plays just fine in PotPlayer. Might be a player-specific issue.
In my case it was because of the encoding methodology of the input file, although it appeared to be Fixed rate it was not as mentioned in Brians response above.
When I clipped out a part of the source with avidemux it was fine but once recoded with shotcut it was not and it was the source file at fault not shotcut.
You’ll love this Brian - get VLC to fix it for you is the answer.
Open VLC
Select advanced controls from the menu.
This will bring up a record button on the playback bar
Play the video from file or from source which is encoded in the fashion you mention above.
Before the video starts playing hit the record button.
Let the video play.
goto your C:\Users\Brian\Videos directory to find the video correctly fix frame rated at 29.970 fps with no jerkyness - Some of your other users might find this useful to convert that pesky variable frame rate stuff to fixed.
Basically VLC is acting as a decoder and letting you record the decoded video 
cool eh.
hey guys 
sorry i didn’t introduce myself… i promise i do it in minutes 
am french… wich means… crappy english… you’re warned XD
Iiiiiiiii got the same issue as many ppl here…
30fps_video —> input
output —> laggy 30fps
wtf ?
don’t shotcut know counting up to 30 ?
take sony vegas ( struggle for ages finding the good parameters ) and export your 30fps shit…
it will be 30fps-non-laggy-shit
okay shotcut is NOT sony vegas… IMHO, shotcut is much better ^^ because simpler ( tho really features-full )
ah also… am on a monster-setup ( compared to what is needed for playing/encoding video )
hmmm am a loooong time former dev ( asm C, C++, Cpizza and… Cobol XD ) and i use to know what
am talkin about when the subject is… sampling or limits effetcs
so plz don’t stuff me up with some… your machine is too weak or your input is too crappy…
I bet my right ball ( plz lemme keep my left one ) this is a damn simple lil side effect in shotcut or mebe
in the codecs i use…
unfortunately, i got only one life ( like most of you ^^ ) and no time to debug on my own thousands lines
i didn’t write… be sure i whish i had !
now if a dev ( i mean… a dev !!! ) wanna have a nice and fair fight
am his/her man ! and it will be a real pleasure !!! i promise for both of us
best regards to the devs ! and also…
i guess they’re not said this enough…
congratz for your work guys !!! shotcut is a lil monster 8-))
hope to hear from you VERY soon !
cool eh.