"Hitching" behavior of animations in the GUI

[aymanhab]

Reported by @nickbianco while testing the latest beta. This is not new to version 4.6 but seems worse than the behavior of the simbody visualizer.

[aymanhab]

Need some clarifications:

1. Is this new behavior vs 4.5?
2. Is this model specific?
3. Is this in live mode (running tools) or playback mode or both?
4. What does the performance meter (Ctrl+D in version 4.6) tell us?

Need to quantify and reproduce this before jumping in to make changes/solutions. Note that Simbody visualizer is not scene-graph based so objects are always generated on the fly while the application reuses the geometry/scene-graph. This makes the behavior potentially more variable especially with things like muscles. Also we run inside a JVM or browser that we don't fully control, just a headsup.

[nickbianco]

After running scaling and inverse kinematics with the RajagopalLaiUhlrich2023.osim model, I created the following two videos: the first recorded directly in the OpenSim GUI (using the test artifact from the recent demos meeting), and the second using the Simbody visualizer.

The video from the OpenSim GUI was recorded using the default video recording option, saved directly to an MP4 file. Here is the result:

Rajagopal_IK_OpenSimGUI.mp4

The video from the Simbody visualizer was recorded by first using VisualizerUtilities::showMotion() to generate the animation, and then selecting the "Save Movie" dropdown menu option to create a set of PNG files. These files were stitched together using the following ffmpeg command:

ffmpeg -framerate 30 -pattern_type glob -i '*.png -c:v libx264 -pix_fmt yuv420p out.mp4

Here is the result (with some missing geometry, but enough to convey the point here):

Rajagopal_IK_SimbodyVisualizer.mp4

The video from the Simbody visualizer is noticeably smoother, free of the "hitching" behavior from the OpenSim GUI video. In addition, both recorded videos reflect the quality of the playback in the respective visualizers. In other words, the "hitching" behavior appears when playing back animations in the OpenSim GUI, not just when recording videos.

Note that the video recorded in the OpenSim GUI is using a build artifact prior to @AlbertoCasasOrtiz's recent in-development changes regarding video recording options. Not sure if those changes fix the "hitching" issue.

[nickbianco]

Is this new behavior vs 4.5?

No, this was present in 4.5 too. I was hoping that the visualizer upgrade would fix this issue, but unfortunately that does not seem to be the case.

Is this model specific?

No.

Is this in live mode (running tools) or playback mode or both?

Playback mode. I don't mind "hitching" when running tools since simulation code is running in the background and there is no way to guarantee a frame rate. However, the hitching in playback mode makes it difficult to record publication quality videos.

What does the performance meter (Ctrl+D in version 4.6) tell us?

Here is a screen recording (taken using the built-in MacOS video recording tool):

Screen.Recording.2025-10-28.at.11.25.39.AM.mov

[AlbertoCasasOrtiz]

@aymanhab @nickbianco I think the changes I am working on should fix this, as there was a race condition that sometimes added jittering in random frames. I will keep you posted.

[aymanhab]

@AlbertoCasasOrtiz I updated the viewer branch to account for the animations being sent from the GUI as well as the animation speed, made the corresponding changes on the GUI side. I wasn't sure what to expect at this stage, so if you can build the GUI branch and viewer branch on your side, it would be great so we can identify the issues, as well as account for recording without an animation in the GUI. Thank you

[aymanhab]

@nickbianco Quick question to clarify as we try to compare the simbody images to those used/created by the GUI. The VisualizerUtilities::showMotion doesn't seem to be doing any resampling or interpolation by default, does the simbody visualizer do any of these downstream or does it write the files corresponding to states as is (# of png files = # timestamps in the state trajectory)? Thank you

[AlbertoCasasOrtiz]

I updated the viewer branch to account for the animations being sent from the GUI as well as the animation speed, made the corresponding changes on the GUI side. I wasn't sure what to expect at this stage, so if you can build the GUI branch and viewer branch on your side, it would be great so we can identify the issues, as well as account for recording without an animation in the GUI. Thank you

Is there any build in actions with the GUI changes and jxbrowser? I am not sure if I have everything needed to build the GUI with the new jxbrowser version.

[aymanhab]

Gui builds against dev branch, I can merge the pr into dev so we have a common integrated build.

…

On Tue, Nov 4, 2025, 9:43 AM Alberto ***@***.***> wrote: *AlbertoCasasOrtiz* left a comment (opensim-org/opensim-gui#1567) <#1567 (comment)> I updated the viewer branch to account for the animations being sent from the GUI as well as the animation speed, made the corresponding changes on the GUI side. I wasn't sure what to expect at this stage, so if you can build the GUI branch and viewer branch on your side, it would be great so we can identify the issues, as well as account for recording without an animation in the GUI. Thank you Is there any build in actions with the GUI changes and jxbrowser? I am not sure if I have everything needed to build the GUI with the new jxbrowser version. — Reply to this email directly, view it on GitHub <#1567 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AA6JY4FAWSGIXKTERRYDVJD33DQT3AVCNFSM6AAAAACKBXRPIGVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTIOBXGMYDKMBUGU> . You are receiving this because you were assigned.Message ID: ***@***.***>

[aymanhab]

Just merged the branch to dev so we should be all in sync

…

On Tue, Nov 4, 2025, 9:45 AM Ayman Habib ***@***.***> wrote: Gui builds against dev branch, I can merge the pr into dev so we have a common integrated build. On Tue, Nov 4, 2025, 9:43 AM Alberto ***@***.***> wrote: > *AlbertoCasasOrtiz* left a comment (opensim-org/opensim-gui#1567) > <#1567 (comment)> > > I updated the viewer branch to account for the animations being sent from > the GUI as well as the animation speed, made the corresponding changes on > the GUI side. I wasn't sure what to expect at this stage, so if you can > build the GUI branch and viewer branch on your side, it would be great so > we can identify the issues, as well as account for recording without an > animation in the GUI. Thank you > > Is there any build in actions with the GUI changes and jxbrowser? I am > not sure if I have everything needed to build the GUI with the new > jxbrowser version. > > — > Reply to this email directly, view it on GitHub > <#1567 (comment)>, > or unsubscribe > <https://github.com/notifications/unsubscribe-auth/AA6JY4FAWSGIXKTERRYDVJD33DQT3AVCNFSM6AAAAACKBXRPIGVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTIOBXGMYDKMBUGU> > . > You are receiving this because you were assigned.Message ID: > ***@***.***> >

[aymanhab]

@AlbertoCasasOrtiz are you able to build/run the GUI with the latest changes?

[nickbianco]

@aymanhab the sampling in VisualizerUtilities::showMotion() happens here: https://github.com/opensim-org/opensim-core/blob/65b568fe5ae363d750d49b418149af5ef334cde7/OpenSim/Simulation/VisualizerUtilities.cpp#L87.

[aymanhab]

opensim-viewer-video_2025-11-10_10-46-03.mp4