"Split at playhead" lagging hard with big 20 gig video

I’m in the process of editing a video I made using OBS. The video is large. 20 gigs in size and I want to edit it down to remove all of the boring bits and leave in all of the interesting parts.

Unfortunately certain actions make Shotcut lag extremely hard. For example if I use the “split at playhead” feature it just causes the shotcut app to freeze up for 30 seconds or more.

I imagine the culprit is the 20 gig video file? Is there anyway for me to mitigate this?

Below are my system specs:

32 gigs of ram (will upgrading to 64 gigs help? I have some bad ram I need to RMA that isn’t in my PC)
6700k CPU
GTX 1080
Windows 10 Pro

Since you are on Windows then I highly encourage you to use this temporary proxy tool: https://forum.shotcut.org/t/shotcut-proxy-videos-auto-creation-auto-replace-tool-for-fast-smooth-editing/14519

I say temporary because it was announced that this year is supposed to be the year when Shotcut’s performance is updated and improved. The first step was taken in the last released version 20.02.17 by debuting the Preview Scaling feature which does help with playback performance in regards to effects being applied. So while the other steps in development are taken towards performance improvement, use the above tool.

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Interesting. Are you suggesting that Shotcut in its current state is a piece of shit or is Windows at fault?

Don’t get me wrong. I love Debian, but I can only use that as a Guest OS inside a virtual machine because I use this PC for VR/Gaming so it’s not realistic for me to use a Linux or BSD based operating system as my primary OS.

I have no idea how you extrapolated any of that from what I wrote.

I have no idea why you wrote that. I didn’t suggest anything about using or not using Linux.

Welp I just did like 4 hours of video editing work. Saved my project. Continued editing. Then Shotcut crashes and somehow takes my entire project with it despite me saving it several minutes before the crash. I reload shotcut and it tells me my saved file is damaged but it will attempt to repair it. The “repaired” file just says invalid in the entire video. Great.

Anyway I can recover this?

What I extrapolated from your post is that this is a Windows specific issue that does not occur in Linux/BSD based operating systems. So either Windows is at fault or Shotcut is at fault.

Anyway I just wasted hours working on a project with a “repaired” file that just shows invalid on my entire editing project. I hope I can recover this. If not, I learned my lessons and will be saving multiple copies of this project because clearly this tool is not stable.

This is most likely the problem. The issue is not the 20 gig size of the file, but rather the complexity of decoding and seeking within the file. Adding more RAM will not help. The same lag would likely happen on Linux for the same reason.

@DRM recommended the proxy tool as a way of changing the decoding complexity of the OBS file. The other option is to do Convert to Edit-Friendly on the OBS file in H.264 format, and then edit on the converted file. These are pretty standard problems and work-arounds on all editing platforms.

Actually, there is one other possible problem… If the 20 gig file is added to the timeline and then you try to start editing immediately, it’s possible that Shotcut will appear laggy because it is busy generating audio waveforms in the background. That could take awhile for a 20 gig file. If you wait a couple minutes until the waveform is complete (scrub to the end of the timeline and see if the waveform is drawn on all audio tracks yet), then editing should get much smoother with that process gone.

If you had gone to the link I provided, you would’ve read that the tool I recommended is only for Windows. It’s not available to Mac and Linux users. Hence why I wrote, “Since you are on Windows…”

@Austin, while we don’t know why his file is so big, OBS does give the option of using Ut Video along with PCM audio wrapped in an avi container for encoding. It’s the Lossless option in the recording quality setting.

“If you had gone to the link I provided, you would’ve read that the tool I recommended is only for Windows. It’s not available to Mac and Linux users. Hence why I wrote, “Since you are on Windows…””

I understand that. I understand the need for your very useful tool when using Windows. But what I am saying is that this appears to be a Windows specific issue (hence the need for your tool) because Shotcut runs less than optimal on Windows correct?

And @Austin you are right that I encoded the file in a lossy compression algorithm which as you pointed out will cause the system to lag and is in fact the culprit (and it would run poorly in Linux or Mac too), and also will degrade the quality of the re-encoded video after the editing process is complete. I will use a lossless format in the future though I imagine that will result in a massive file size.

It’s not my tool. Someone else made it.

I’m on Windows 10 too and I don’t have the issue that you have where lag happens just by attempting to make cuts to the clip. I just tested a video file that’s over 20 gigs and runs almost 2 hours on Shotcut and did several random cuts on it no problem with no lag. And I did this while the audio wave form was being drawn up by Shotcut.

The only reason that proxy tool is only on Windows is because the creator of the tool is on Windows. He doesn’t use Mac or Linux and no one has ported it over to Mac or Linux.

A proxy workflow is common place for video editing. If you for whatever reason are experiencing lag, use the tool I linked to above and see if it helps.

I don’t know how long your video file is but one issue that Shotcut currently does have where it always lag is if the video file is over 90 minutes long or so and you are zooming in and out of the timeline. The zooming in and out will always lag.

There is still a disconnect here. This lag problem would exist on all platforms. It is not a Windows-specific problem. We don’t need the tool because we’re running Windows… we are fortunate to have a solution in the form of a Windows-only tool. The other platforms would have to home brew a solution.

Likewise, Shotcut runs equally well on Windows and Linux. Linux has no performance advantage according to export times of some really big 4K files (although technically, hardware and driver configuration could slightly influence this either way).

You are so right. :slight_smile: You are correct that a generation of loss will happen due to re-encoding. However, there’s a practical side to it. If OBS is creating a huge file of high quality already, and encoding output is also high quality (like H.264 CRF 16-20), is the loss really visible enough to be worth the space and hassle of lossless codecs? Probably not, but it’s ultimately up to your requirements of course.

If you want a similar-sized file (not a huge lossless file) that will edit much more smoothly straight out of OBS, then try these settings:

OBS Settings > Output tab > Output Mode = Advanced > Recording tab:
Type = Custom Output (FFmpeg)
FFmpeg Output Type = Output to File
Container Format = mp4
Video Bitrate = up to you
Keyframe interval = 1
Video Encoder = libx264
Video Encoder Settings = vprofile=main bf=0 preset=veryfast movflags=+faststart
Audio Bitrate = 384
Audio Encoder = aac

This will build an all-intra file from the start, which should edit smooth without being a huge lossless file.

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