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MovieStim3 issues regarding high fps


Hi everyone!

I’m having issues with visual.MovieStim3. I saw a relevant conversation between Samuel Mehr, @jon and @sol dating back to 2013/2014.

My video is playing at 60-70 fps effective (measured with .recordFrameIntervals) while it’s encoded at 120fps (119.88 to be precise) and I need it to play at this frequency. It’s dropping half the frames, effectively. It’s not massively high definition, just 720p, yet reducing the pixel number by encoding it as 240p increases the fps to roughly 120. Even so, it’s not quite right, I get a lot of jitter in the fps and I need it to be very precise.

My new lab computer has an AMD Radeon Pro WX 3100 graphics card and a separate Asus sound card, I’m running Windows and PsyPy3 on Anaconda Python 3.7.

Let me know if there’s any other relevant info or if there’s any alternative to MovieStim3 that I can try!



Does the movie include audio? How much RAM do you have? How long is the movie overall? What is the movie’s encoding format (e.g., h.264, MPEG, etc.)?

All that might or might not matter, but it’ll help me narrow down. The way MovieStim3 handles audio tracks can be extremely inefficient, though usually that manifests as just outright crashing rather than frame drops.

As for whether there are alternatives, not that I know of but I’d be interested to hear if there were. MovieStim2 is still in there and technically works (sometimes) but I don’t know that it’ll be more efficient. Fundamentally MovieStim3 is running on MoviePy, and a lot of its issues are due to MoviePy’s general inefficiency, but as far as I know there’s no better Python-based solution for loading movie files.


@jonathan.kominsky Thank you for your answer!

  1. Just tried playing with the audio on mute [noAudio - True] and also tried removing the audio from the movie altogether on encoding but to no avail.
  2. RAM is 16GB. This question made me think of something: is there any way to load the whole video to the video card before I play it? I’m already using the ISI function where I give PsychoPy 15 seconds before I start to load the video but that doesn’t help either.
  3. Movie is encoded in h.265 because it’s the only way I can export from Premiere CC at 120 hz I think.

Even trying the simplest builder view set up with just a 3 second video yields the same result. There is a choice to change the backend to “avbin” but I get the following error: AttributeError: module ‘’ has no attribute ‘ManagedSoundPlayer’. Using Opencv as the backend yields the following error: ImportError: dlopen(/Applications/, 2): Library not loaded: @loader_path/.dylibs/libavcodec.57.107.100.dylib
Referenced from: /Applications/
Reason: image not found.

Any ideas of things to try are very welcome!


Essentially, you’re pushing things really hard!
Even 720p is nearly 1,000,000 pixels per frame, so 3 million numbers (RGB) that PsychoPy has to read, convert and push to the graphics card in less than 8ms to meet your timing needs. That’s tough going.


By turning off waitBlanking for the window you might get some slightly better performance (it allows the system to work a frame ahead if it has a chance.

Make sure everything else is down to an absolute minimum in terms of processing (don’t do other calculations in the each-frame, try not to minimise anything else on screen, especially get rid of text)

Otherwise, it’s time to get your hands dirty inside the movie code and try to find additional optimizations in the rendering code.


I’m also trying to play 1920x1080 video, but at 60Hz, not 120. The relevant conversation link you provided is giving me hope. I’m currently getting only 30Hz, but my machine is not exactly very beefy. I’m planning to test this on another machine soon.

My problem though is slightly different. I have the movie set to loop, and there is a noticeable lag each time the video restarts.Using @enricovara 's mention of .recordFrameIntervals led me to look at that section of the manual. I saved the frame intervals to a file and found that every 61 frames (the length of the AVI), the frameInterval was ~ 0.14sec instead of ~0.03sec.

Hopefully, on a faster machine, I will get 60Hz, but I still notice the delay each time the video loops.

We are in the process of making longer videos so this is not as noticeable, but is there a way to minimize this delay in the video looping?


Does the movie have audio? If so, it’s probably not possible to minimize the delay. Every time you loop (or seek), PsychoPy reloads the entire audio track for a movie file. If there’s no audio, I’m not sure.


@jonathan.kominsky, No audio. I also tried it on the machines the experiment will actually be run on. Still 30Hz, but the “rewind” time went from 0.14sec to 0.08sec.

ImageJ plays them at 60Hz with no problem. Also no pause each loop, but I suspect ImageJ is doing this all in memory.


Yes, I suspect the delay is due to initially accessing the file from disk. i.e. if you create the movie stimulus in a loop, or update an existing stimulus’ movie file attribute in a loop, the disk reading happens once each time the loop runs. Hard to know without seeing your code, but you might avoid this by creating the movie stimulus just once, before the loop starts. Then within the loop, you just have your_movie.draw() commands. This avoids going back to the disk to initialise reading from the movie file.

To reset the movie to the start, you should be able to just once it has played through, ready for the next iteration.


Thanks @jon and everyone!

Can someone explain to me what’s happening under the hood a little, please? If I understood well psychopy is calling moviepy and loading the video in RAM and then passing each frame onto the graphics card and displaying it? And it’s this passing to the graphics which is ‘slow’? Or are we not sure of what the bottleneck is either, for my case?

Why does opening the video simply on VLC work fine? Can anyone think of a way to implement whatever VLC is doping in python?

Thanks again for the amazingly quick support!


What’s happening under the hood?

We use moviepy, which uses ffmpeg to load the movie as a stream. Movies are loaded one frame at a time (once in memory your video is uncompressed raw numbers and that quickly consumes hundreds of gigabytes of memory [see note 1 below] so we can’t load all frames in advanced).

Why don’t we achieve the performance of VLC?

The key differences are:

  1. VLC Is written in C (whereas PsychoPy is written in Python)
  2. VLC only has one thing to do, and can dedicate all resources to that one key task of translating pixels, whereas PsychoPy is trying to capture responses and present other stimuli all with high precision
  3. VLC has many developers with a specific interest/expertise in video rendering, whereas PsychoPy is written by behavioural scientists borrowing libraries from other places
  4. Possibly VLC pre-buffers a few frames in advance to get a smoother transition. I don’t know enough about that (see point 3)

[1]: You were talking about 720p at 120Hz: each frame is 720x1280x3 values at (probably) 16 bits each = 5529600 bytes (roughly 5.5Mb) per frame. At 120Hz that’s ~650Mb per second, or 2.38 TB per minute of movie!


@Michael, all I’m doing is setting movie.loop to True. I just played my video with ffmpeg from the command line, and I can see when the video restarts, so that’s out of PsychoPy’s hands. Why it’s playing at 30fps instead of 60fps though, I need to look into a little further.
Yesterday I tried to change the backend to opencv, but I got an error.

################## Running: C:\Experiments\testAVI\ ##################
pygame 1.9.4
Hello from the pygame community.
Traceback (most recent call last):
  File "C:\software\condaenvs\perceptionlab\lib\site-packages\psychopy\visual\", line 110, in <module>
    import vlc
ModuleNotFoundError: No module named 'vlc'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Experiments\testAVI\", line 75, in <module>
  File "C:\software\condaenvs\perceptionlab\lib\site-packages\psychopy\contrib\", line 119, in __call__
    obj = object.__getattribute__(self, '_resolve')()
  File "C:\software\condaenvs\perceptionlab\lib\site-packages\psychopy\contrib\", line 88, in _resolve
    obj = factory(self, scope, name)
  File "C:\software\condaenvs\perceptionlab\lib\site-packages\psychopy\contrib\", line 203, in _import
    module = __import__(module_python_path, scope, scope, [member], level=0)
  File "C:\software\condaenvs\perceptionlab\lib\site-packages\psychopy\visual\", line 116, in <module>
    if "wrong architecture" in err.message:
AttributeError: 'ModuleNotFoundError' object has no attribute 'message'

Maybe I need to get vlc installed on this conda environment to see about playing back at 60fps.


Thank you Jon, very kind of you to spend time explaining.

I’ll try a few thing and let you know how it goes!


You were talking about 720p at 120Hz: each frame is 720x1280x3 values at (probably) 16 bits each = 5529600 bytes (roughly 5.5Mb) per frame. At 120Hz that’s ~650Mb per second, or 2.38 TB per minute of movie !

That’s not surprising anymore. Modern video hardware can push out considerably higher data rates than that. DisplayPort can presently handle 4K (3840 × 2160) at 120 Hz with HDR color.


Yes, a high performance graphics card can do it (once the data are in the right format). I’m just pointing out that there’s a lot to do because we also have to fetch the data from the disk as well, and all this being done by intermediate libs like ffmpeg, which probably means multiple conversions.


Ok, so I got vlc installed so I could use the opencv backend. I’m getting slightly better framerates, but still not 60fps. I turns out though, that if I norm units instead of pixel units with the opencv backend, I get better still, and I don’t get the “rewind” time issue that I have with moviepy (ffmpeg). The rate for moviepy is more consistent though.

Here’s a table I built of the framerates (1/frameInterval) for each run. I use a 1920x1080 60fps AVI video as the stimulus. I’m just pasting the first second of the 10 second flow.

frame norm moviepy norm opencv pixel moviepy pixel opencv
0 81.0275113 8.425651711 47.58949857 15.03251656
1 37.13802383 50.61246717 32.525033 12.12996953
2 12.22950036 38.64743655 28.49226082 28.60810586
3 39.63892765 58.74473113 11.88743079 44.83831596
4 34.31444803 45.05013813 34.42518905 39.17145116
5 36.28213541 54.47011459 27.37191687 48.7994721
6 36.16818448 60.75214473 32.72749083 35.87809662
7 32.64979296 13.96118867 31.89507982 51.59242272
8 36.3149947 26.5415454 30.61610786 49.83788316
9 36.20083752 42.47168872 30.14277431 35.54548756
10 36.3558546 55.4040951 30.26557782 48.49160023
11 37.82861819 38.87677415 29.16746125 44.89274968
12 36.01748867 42.17726965 31.08275663 41.75238045
13 37.87985429 44.30940875 31.58661797 53.85226789
14 33.98298875 46.72100409 30.97341112 34.98133272
15 37.98751296 46.48023126 31.02509512 51.78669914
16 36.31975033 43.9780118 30.3963248 50.25403913
17 33.06105338 48.07760319 30.93972185 34.00416861
18 27.84644863 59.6427304 31.13801071 51.2326473
19 35.29555744 42.34793224 32.26082993 49.35087049
20 23.52845861 35.17580912 31.81306698 35.64943171
21 35.11901821 45.76187653 31.03522103 50.87941062
22 33.9113122 4.978874978 31.84320107 47.03929206
23 36.08191852 15.22569607 32.14740116 35.78320149
24 31.12839985 46.105479 31.81154652 33.1262093
25 32.62131087 56.08851135 31.98550714 52.01494136
26 36.47379095 36.08583076 30.59753057 50.72431862
27 37.69024484 25.62815911 31.96768772 34.88636153
28 36.41193845 56.0082798 32.67158819 34.41842474
29 34.26428226 57.58099617 32.41605547 43.21733825
30 37.72527769 36.48938692 31.18615417 34.55959957
31 36.09483218 48.63118831 31.48323259 6.116211031
32 35.91914176 59.10360507 31.92047032 16.48777829
33 36.38765406 57.37650194 30.96159713 50.26011059
34 37.10614101 57.99034699 29.83874409 35.62539072
35 36.12696069 59.65235152 31.60251442 35.77012529
36 37.57874534 38.05962606 31.32440445 43.68648762
37 37.0178186 55.93015704 31.61151954 32.60022142
38 34.9923667 48.71375879 32.80523608 50.59400132
39 37.98187712 35.24397712 31.85813697 45.55205165
40 36.33362812 44.98863164 31.39443451 36.42429216
41 36.48138728 58.87463057 31.24001727 35.7601324
42 36.09130938 36.47419068 30.06462572 48.83312539
43 36.12421579 44.28994996 31.3261735 50.16541305
44 36.95657099 38.56414179 31.49723651 33.73771126
45 35.32740314 44.0735238 31.01035193 48.67101488
46 36.63398206 33.94140022 31.30319134 45.80092212
47 36.76144614 35.36494237 31.43090275 41.93968872
48 37.53170562 39.55459953 30.77123073 52.80724802
49 36.28173988 59.3608246 32.34988675 34.05984815
50 37.46916907 55.85693918 31.72330831 49.58763923
51 36.80942323 54.30745888 30.60090661 48.39007224
52 37.25108843 40.1675678 30.86884013 34.39921449
53 37.14880175 47.39432091 30.50442242 34.74359808
54 35.96183525 48.91135139 31.69219345 43.69279644
55 37.000945 41.29493515 31.15637521 47.65355092
56 36.21107834 48.39218306 32.02644392 35.62996744
57 36.03113631 48.69237746 31.22008968 35.21190903
58 34.96369288 55.86162687 31.09902162 50.0116308
59 35.49658171 37.08505393 31.5755299 49.06132445
60 7.411824179 29.87436718 7.048496849 33.99756873

testAVI.psyexp (7.7 KB)


I tried this on a few more machines, and it turned out that I can get 60fps using the NVidia control panel. The 4k monitors we have run at 30Hz, but if I set them to HD mode (1920x1080), they can refresh at 60Hz. I lose a lot of desktop real estate, but I can display a 60Hz HD AVI file at 60Hz.

As for moviepy vs opencv backends, I still have my “rewind” time issue with moviepy, not with opencv. However, the moviepy framerate is more stable. The opencv framerate jumps around a lot.

In the moviepy module, FFMPEG_VideoReader has a bufsize argument in, but the VideoFileClip class doesn’t supply the bufsize when it creates it’s FFMPEG_VideoReader instance.

In FFMPEG_VideoReader.__init__:

        if bufsize is None:
            w, h = self.size
            bufsize = self.depth * w * h + 100

In VideoFileClip.__init__:

        self.reader = FFMPEG_VideoReader(filename, pix_fmt=pix_fmt,

I’m going to try and modify this and to be able to pass in a buffer size so I can fit the entire 1 sec movie in memory. Not sure if it will help, but it’s worth a try.


On second thought, maybe only a 2-3 frames instead of just one.

Changed a few lines in psychopy/visual/, moviepy/video/io/, everything locks up. Putting things back like they were. Not worth the effort.