Motion blur making random jitters.

Ill start by saying that I've known this issue for a long time and decided to instead use motion trails as an artificial motion blur. It of course is not the same though. So now I really want to get to the bottom of this. Why is it that when I apply motion blur to my edits that they end up at random times jittering? It happens with text slowly getting larger or even not moving at all. I feel like whatever detects the movement gets confused or something and causes random spikes in movement. Its not entirely crucial but it would be nice to have.


  • Have you been applying the motion blur effect (from the effects list) or using the motion blur property (the toggle on a 3D layer)? 

    If the motion blur effect, are you placing it directly on the text layer or on a grade? 

  • I am placing the effect directly on the timeline and the text I'm referring to is not being generated by hitfilm but rather just the text in the video. I may also not have much idea as to what certain settings in the motion blur effect actually do, usually I just adjust sliders to make the motion more fluid and leave it at that.

  • Ah. Well then... Your guess is correct. The "motion detection" gets confused.

    Long story shortish--When bringing in video, all Hitfilm (or any other photo/video editor) sees is a matrix of dots that have color values assigned. Hitfilm (or any other photo/video editor) doesn't understand the content of the image. It doesn't know what's text, what's a person, etc, etc, etc, unless the artist defines things for the software. It's just dots.

    The motion blur effect tries to analyze the colors of individual dots in a frame, then compare those dots to the dots of the next frame. It attempts to match up similar groups of dots then compares position changes of these groups between frames. From there it uses the motion blur effect, which is defining a virtual camera shutter, to try to create the trails.

    So... You've brought in video that already has text overlaid on it--maybe videogame footage? Ok. Whatever your footage is, it's still just dots. Changes of pixel patterns around the static text will be interpreted as "movement" and this can and will (obviously since you're seeing it happen) cause occasional artifacts.

    I'm not going to get into all the Motion Blur Settings, because I don't actually understand all the Optical Flow settings myself (one day I need to look that up), but those are the settings that control how Hotfilm attempts to track the pixel motion. The SHUTTER Angle/Phase settings are pretty simple. Angle controls the amount of blur, and, for "realistic" settings the Shutter Phase should be "negative one-half" of the Angle. I.e. Shutter Angle of 180 should have a phase of -90. Accessing those controls in the Motion Blur effects requires changing the Mode from Comp Settings to Custom. Or, changing the master Motion Blur settings in the Composite Shot Properties.

    Motion Trails is a much simpler effect. It's pretty much just overlaying duplicate frames over the video, so it's easier to control--because it's not a motion blur effect, but just duplicating low-opacity versions of surrounding frames. In this case there's nothing to "confuse" the text edges

  • Ok, some parts of my footage have no text at all and it still bugs out. But I get your point. The software cant determine what everything is. However the text I mentioned is not being surrounded by erratic movement. This is the video I'm trying to add motion blur to. (The video doesn't have any motion blur applied). The areas where the text are don't have too much erratic movement around them. Which is why I'm confused that is acts weird. Ill upload an unlisted video where I applied the MB so you can see. Something reminds me of a hitfilm patch that fixed something with motion blur a while back. Not sure if I was dreaming XD.

  • Awesome video!  Watching that, I don't feel that it needs motion blur applied.  It looks just fine as-is.  It's playing at 60fps, so visual stuttering during high-speed moments is practically nil.  Why add motion blur?

  • Ah... Motion blur algorithms were designed to deal with mostly linear motion. This type of muti-axial rotation and movement is probably beyond what the algorithm can handle. It's all dots. 

  •  jsbarrett. It is mostly an example and maybe a little bit of an experiment. :) Just to see how smooth I could possibly make it! XD

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