10 Replies Latest reply on Aug 25, 2010 8:57 AM by Jon-M-Spear

    Uh-oh: the motion judder issue again

    Jon-M-Spear Level 4

      I recently produced a composition in AE CS5 which comprised still images traversing the screen as if a camera was constantly tracking left to right.  The comp was 25 fps PAL widescreen square pixels.

       

      The judder - both in ram preview and rendered output caused my client to complain.  (This was on a 40' screen, but very noticeable on my comp monitor).  It was not a consistent jarring - as if it was wrong field order or an interlacing problem, nor is it caused by memory bottlenecks or disk speed.

       

      This was the first comp I had produced on CS5, and do not recall judder as pronounced as this on CS4 or 7.

       

      I have subsequently tried to rebuild the project using different formats, frame rates, output settings and tracking speeds, all to no avail.   Motion blur increases the problem.

       

      I know that there has been some detailed and extremely valuable discussion about the probable causes of judder on this forum, but I can't seem to corrolate those issues with my own experience.

       

      I have posted an 11 sec single image track at www.jontysexton.co.uk/motion/judder.wmv

       

      I'd appreciate feedback from one of you AE gurus.  Thanks.

        • 1. Re: Uh-oh: the motion judder issue again
          Rick Gerard Adobe Community Professional & MVP

          This looks like a typical stroboscopic speed issue. Try making sure that the image is moving an whole number of pixels per frame. IOW 3 pixels per frame exactly or 4 pixels per frame or 9 pixels per frame rather than 3.2 pixels per frame.

           

          Hope this helps.

          • 2. Re: Uh-oh: the motion judder issue again
            Jon-M-Spear Level 4

            Hi Rick.  Thanks for your suggestion.  I'll certainly

            give it a try.

            • 3. Re: Uh-oh: the motion judder issue again
              Jon-M-Spear Level 4

              Hi Rick.  I'm not seeing any difference in the stutterinhg by setting a whole number of pixels per second.

               

              I have produced two comps in which I have set two differing multiples of 25 (fps).  The first is 500 pixels per second, and the 2nd is 250.  They both appear to stutter the same amount.  Motion blur or frame blending are not set.

               

               

              www.jontysexton.co.uk/motion/500pps.wmv

              www.jontysexton.co.uk/motion/250pps.wmv

              • 4. Re: Uh-oh: the motion judder issue again
                TimeRemapper Level 4

                What is your final playback method? DVD? Hard drive?

                • 5. Re: Uh-oh: the motion judder issue again
                  Pompey (formerly J-MS) Level 1

                  At the moment the means of delivery is academic.  I am getting judder during creation and whatever format it is output to.

                  • 6. Re: Uh-oh: the motion judder issue again
                    Jon-M-Spear Level 4

                    Sorry.  Not sure what happened to my profile details on the last post!!

                    • 7. Re: Uh-oh: the motion judder issue again
                      TimeRemapper Level 4

                      Would you mind taking the time (despite your considering it being academic), to please indicate the ultimate delivery method? If for some reason you're not tied to, let's say, a PAL DVD, and you were playing off of a decent hard drive, you could increase the frame rate and possibly eradicate the problem altogether...

                       

                      You may be seeing a refresh rate vs. frame rate issue. Your ultimate playback device will help determine what the limits are, and appropriately, help determine how best to provide workarounds or solutions.

                      • 8. Re: Uh-oh: the motion judder issue again
                        Jon-M-Spear Level 4

                        Hi TimeRamapper.

                         

                        When I say it's academic, what I mean is that it is often out of my control.  It depends whether I am producing a DVD for general distribution or creating a video piece for conference play-in.  If the latter, the production company will tell me what delivery means they want.  It may be laid off onto PAL DVcam , Quicktime or wmv.  Sometimes the DVcam is captured on a media server and played into the conferenceI from that.

                         

                        I have been producing graphic-based conference openers since around 2000, and have not been aware of such pronounced juddering  - unless it's caused by interlace flicker or field reversal.  I've certainly never had a client complain before!

                         

                        It's not just in the subsequent playback that it becomes apparent. It is visible in AE ram preview (and Premiere Pro if I create a motion path on a still photograph).  I have increased frame rate to 50 fps but that does not eliminate the problem - or reduce it sufficiently to be acceptable.  

                         

                        My drives are 7200 Raid 0 and the 12MB ram is hardly being put under pressure during ram preview.

                        • 9. Re: Uh-oh: the motion judder issue again
                          TimeRemapper Level 4

                          I believe what you're seeing is a result of horizontal movement (at a given speed and temporal resolution) across the canvas of an object with a sharp vertical edge. To some extent, I think that you're going to get that result no matter what.

                           

                          However, you can try applying the following expression to the Position property:

                          [Math.round(position[0]),Math.round(position[1])]

                           

                          It will ensure that whenever the object lands, it will land on whole pixel increments only, not subpixel increments. It may provide a result that you're happier with in the long run, albeit less mathematically correct (rounding).

                           

                          You may also want to consider duplicating your travelling layer, and applying a slight horizontal Fast Blur to the bottom layer. It may help the harsh edge to appear to blend into whatever background you're using. This would avoid creating motion blur on the content itself.

                          • 10. Re: Uh-oh: the motion judder issue again
                            Jon-M-Spear Level 4

                            Hi TimeRemapper.

                             

                            I appreciate your input, thanks.

                             

                            I have applied the expression and tried differing speeds, durations, pixels per second and frame rates, but nothing seems to lessen the judder.

                             

                            You suggest that it may just be the edge wavering, but I'm pretty sure the whole of the content judders  - and inconsistently at that, becoming worse when it's over half way through the travel distance.

                             

                            I've even put it on a 3d layer and tracked the camera across, but the result is the same.

                             

                            One does see smooth pans/tracks of stills/picture-in-picture.  How are they achieved?

                             

                            Here's the latest with the expression applied:

                             

                            www.jontysexton.co.uk/motion/comp-expression.wmv