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I have read a lot of posts here and on other forums about Blender being painfully slow, to the extent it closes in on being unusable. Here is my scenario:

  • I have a 11 second 4K video (30 MB file) that I import into Blender "Video editing"
  • I drag the video onto the timeline/sequencer
  • When I drag the time-marker, it is super laggy, updating maybe once every second
  • When pressing SPACE to play the recoding, the framerate is around 5

Hardware:

  • AMD Ryzen 9 3900X 12C on base clock 3800 Mhz (on GIGABYTE X570 AORUS ELITE)
  • NVIDIA GeForce RTX 2070 SUPER, 1605 Mhz, 8 GB memory
  • 32 GB DDR4 RAM
  • Samsung NVMe SSD (4x 8.0 GT/s)

Software:

  • Windows 10 x64
  • Blender 2.91.0 (latest, installed from Steam due to this post)
  • Blender is set to use "CUDA" under Preference --> System; my graphics card is selected
  • Win, Blender and the video file are all placed on the same NVMe SSD drive
  • Nothing else is running except the basics; CPU and GPU is idle, plenty of RAM available, as well as space on drive

I suspected something weird with the video file itself, so I took a look at it in MediaInfo. This info doesn't tell me much:

enter image description here

Anyways, I thought that maybe the video file is bad somehow, so I imported it into Adobe Premiere (latest version), and the video works fine there, no lagging, smooth time-scrolling and playback.

Here is a video of the Blender lag: https://screencast-o-matic.com/watch/cYlO6c878q

  • Note that I am click-and-dragging the time-marker, so I am holding it all the time
  • Both drag and playback is extremely laggy as you can see
  • Note that it is not the Blender UI that is slow; it isnt, its snappy and fast

Here is a video of the same video file imported into Premiere: http://somup.com/cYlO6e27hY

  • As you can see, its smooth and fast

The above leads me to conclude that it is not the specs of the computer, the hardware, OS or the video file; this seems to be a Blender-specific issue.

Questions:

  • Is this lag in normal / expected behaviour in Blender?
  • I read some "hacks" around it, to use some lowe-resolution hacks, but I am not after hacks, I wanna know if this is normal, or if I am missing something?
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2 Answers 2

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The answer is in your first paragraph Blender being painfully slow, almost unusable.

Blender is a wonderful app to create 3d content, but is the video editing aspect is not adequate for today's needs.

But the real problem lies in the way the video is encoded.

Yes, the media info on the question shows a non standard frame rate (29.252). Most likely the video file is using a variable frame rate scheme to compress the video (some phones and screen recorders will do that to save disk space). Blender cannot handle such files without converting them to a fixed frame rate first.

With the hardware you are using, any other dedicated video editing app out there should work just fine for 4k content. There should be no need to downgrade/transcode/or create proxies of your original video.

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  • $\begingroup$ Thanks for that input. I was actually following this YouTube tutorial: youtube.com/watch?v=hymtATx1QXw&t=205s and on that time (205s), he converts the video into a series of JPG files, as he claims its better to work with in Blender. I do this, and then start a new project and re-import but this time the JPGs. And still, it lags incredibly bad... $\endgroup$
    – Ted
    Commented Dec 26, 2020 at 13:37
  • $\begingroup$ Is it an outdated editing app? I heard it was the most modern and the one that was up-n-coming, but my info is bad? What is a good tool for adding CGI / animated characters to a video clip? $\endgroup$
    – Ted
    Commented Dec 26, 2020 at 13:38
  • $\begingroup$ Acually, i tested it again, by first exporting as a JPG sequence (90% quality), and then starting a new project, going to Movie Clip Editor, importing all the images. When I now press play, it is way more managable (but not perfect). EDIT: Seems the image sequence now is full HD, not 4K anymore... Maybe thats why. $\endgroup$
    – Ted
    Commented Dec 26, 2020 at 13:51
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    $\begingroup$ Blender is a wonderful 3D app, but a lousy video editing one... It is just silly that you have to transcode to work in blender... Any decent video app can do 4k with no hiccups with the hardware you have. $\endgroup$
    – susu
    Commented Dec 26, 2020 at 17:54
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Unfortunately, I believe this is 'normal'. It's 4k video, so it takes a lot to edit and needs a lot of optimization that is just not there yet.

Make sure you update your video drivers because if they are not up to date that might cause issues, but I think it will lag some in any case. I would not consider using lower resolution preview a hack since that is what is done in many video editing aplications in situations like this, it is a pretty standard thing to do. Video editing in Blender is being very actively improved at the moment so you can also try the experimental nightly builds, however be aware that they are in development and might be unstable so maybe save your work more often and save a backup file from the stable Blender version.

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  • $\begingroup$ Alright, thanks for the answer. And maybe I mis-wrote a little; I just want to avoid having to pre-process or otherwise make settings everytime I add a 4K video; I would want to have that "out of the box", like it works in Premiere for example. I will now test with HD mterial, see if that lags. $\endgroup$
    – Ted
    Commented Dec 26, 2020 at 13:34

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