21.x.x UI lag when timeline loaded

I’m seeing a ton of lag in the 21.x.x shotcut releases that wasn’t present in 20.11.28(what I keep going back to) it doesn’t matter what my display method is(i’ve tired them all) when videos are on the timeline the UI turns to a laggy mess in some parts, I think it’s related to the updated QT version but I’m at a loss on what to even do to try to troubleshoot it.

I went ahead and recorded it on video, you can see i’ve got ~20 minutes of video on the tlmeline(I’d love to edit my 5 hour long project but that just seems to get slower the more I add) the system is nearly idle with 2x8 core cpu and 256gb of ram regeresting under 10% as well as the gpu only showing a few percent load from OBS doing the screen capture, it’s actually snappy until the timeline is loaded.

I’ve attatched a paste of the full shotcut-log as well [Info ] <Application::Application> Starting Shotcut version 21.05.18 [Info - Pastebin.com

Description sounds consistent with some other reports:

Do you see any difference if you disable audio waveforms in the timeline?

Turning off the waveforms(or maybe it was disabling the "high performance waveforms I turned off both to be safe) didn’t solve it but definitely helped, I still see a delay with a project opened clicking on something like settings but it’s not nearly as bad as it was with them enabled
I’m also noticing this line in the log [mlt_producer avformat-novalidate] “E:/Shotcut Products/dell lego/proxies/b2321e48b25146a0ccc368103265a6d0.mp4” missing hwaccel parameters. skipping hardware initialization is the format used for proxys by default not something that nvenc will decode?

Just to add to this topic…
I’ve been using Shotcut for a couple of years now and have updated regularly. I was getting terrible timeline lag with the version from 18th May and tore my hair out trying to work out what the conflict may be. I uninstalled everything recent (except for Windows updates) to no avail. I’ve rolled back to a version from September last year (before the big changes) and that’s working perfectly.
As an experiment I tried it on my old HP laptop (which hadn’t had the updates yet) and the up to date version worked fine, but after the Microsoft updates (which hit my primary machine on 21-25 May) the lag started on that one too. I’ve no idea why those updates might be causing the conflict for me, but they seem to be connected in some way on the 2 PCs I’ve looked at. I’ve screen grabbed the updates concerned below.

Ignore that. It does not apply to Shotcut.


This version includes the newer Qt version you refer to.

Good to know it’s not the QT upgrade, although that leaves me in the dark on what to try next, I did notice a ton of dropped frames in the log for the most recent version that weren’t in the older builds.

Any other ideas outside of the waveforms?

I do not have any other quick ideas. Some things you could try if you are interested in helping to try to narrow/debug the problem:

  1. Try a different computer to see if it is specific to this hardware
  2. Try to make variations on the project to see if there is a specific feature that you are using causing hte problem (a filter, a specific file type, a long clip, etc)
  3. try a different video card
  4. Check each release version of Shotcut going backwards in time to identify the exact version of Shotcut where the problem is introduced.

If you can help narrow the problem to a specific feature, file, version or usage, then that can help us determine the problem.

I haven’t had time to do this all on my laptop so i’ll have to follow up soon however,

I took time to go through a bunch of different versions to test this with a 35 minute project I did last night(and even tested a few earlier versions) here’s the results

10.09.27 Seems faster than 10.31 or 11.28 large 5 hour project isn’t causing multiple delays between presses(maybe I can finish it)
20.10.31 behaved fine seems to work as well as 20.11.28, opened 5 hour pain project for comparison which still tended to lock up
20.11.28 works “ok” bigger projects(longer than 1 hour) seem to slow down
21.01.29 UI unresponsive on 35 minute test project(one I edited just fine in 20.11.28 the night before)
21.02.27 UI unresponsive on 35 minute test project(one I edited just fine in 20.11.28 the night before)
21.03.21 UI unresponsive on 35 minute test project(one I edited just fine in 20.11.28 the night before)
21.05.01 UI unresponsive on 35 minute test project(one I edited just fine in 20.11.28 the night before)
21.05.18 UI unresponsive on 35 minute test project(one I edited just fine in 20.11.28 the night before)

  1. The project used for this testing is “fairly typical” of my editing which in this case means 3 tracks and a mix of mkv and mov files with everything as proxies(so file format should be whatever shotcut likes best) a few sections sped up and then a few text filters, nothing crazy

  2. I’d love to but the shortage means I don’t have any spare cards sadly

so it looks like whatever happened started with 10.31 and has gotten progressively worse.

Hardware wise I have
my laptop:
Thinkpad P50
Windows 10 20H2
32gb DDR4
quadro M1000M

My desktop:
Windows 10 20H2
2x E5-2667 V2
256Gb DDR3
quadro RTX 4000
lots of drives(I edit on a 1tb NVMe)

I took time on my thinkpad and sadly seem to have come to the same conclusion, anything newer than 20.10.31 starts to show slowdowns, I can try on a system without nvidia graphics but I honestly expect most of those that I have access too to be terrible for other reasons(mostly they’re at best a 4th gen i5 with an intel IGP)