`Succession` not working properly with `run_time` argument of `Scene.play()`

[ArthurMartensson]

Description of bug / unexpected behavior

The Succession animation group doesn't behave as expected with the play_time keyword argument to Scene.play(). Instead of adjusting the speed of the animation, each animation sent to Succession will have a run_time of 1, and setting run_time=x in Scene.play() will result in an animation that plays the first x animations passed to the Succession in x seconds (including playing the last of those animations partially if x is not an integer), and then skip immediately to the end of the animation.

Expected behavior

I expect a Succession to adjust the play speed of each of its components according to run_time so that each animation passed to the Succession is played, in order, each taking an equal amount of time, totalling the time passed as run_time

How to reproduce the issue

Code for reproducing the problem

class Test(Scene):
  def construct(self):
    s1 = Square(color=RED).shift(LEFT)
    s2 = Square(color=WHITE).shift(RIGHT)
    s3 = Square(color=BLUE).shift(UP)
    s4 = Square(color=GREEN).shift(DOWN)
    a = Succession(Create(s1), Create(s2), Create(s3), Create(s4))
    self.play(a, run_time=1.5)
    self.wait(2)

Additional media files

GIF

Logs

Terminal output

Manim Community v0.15.2

[05/07/22 06:08:26] DEBUG    Hashing ...                          hashing.py:343
                    DEBUG    Hashing done in 0.019071 s.          hashing.py:355
                    DEBUG    Hash generated :                     hashing.py:358
                             3163782288_966638411_2358810818                    
                    INFO     Animation 0 : Using cached     cairo_renderer.py:75
                             data (hash : 3163782288_966638                     
                             411_2358810818)                                    
                    DEBUG    List of the first few          cairo_renderer.py:84
                             animation hashes of the scene:                     
                             ['3163782288_966638411_2358810                     
                             818']                                              
                    DEBUG    Animation with empty mobject       animation.py:173
                    DEBUG    Hashing ...                          hashing.py:343
                    DEBUG    Hashing done in 0.009540 s.          hashing.py:355
                    DEBUG    Hash generated :                     hashing.py:358
                             2201830969_3375341780_1355695238                   
                    INFO     Animation 1 : Using cached     cairo_renderer.py:75
                             data (hash : 2201830969_337534                     
                             1780_1355695238)                                   
                    DEBUG    List of the first few          cairo_renderer.py:84
                             animation hashes of the scene:                     
                             ['3163782288_966638411_2358810                     
                             818', '2201830969_3375341780_1                     
                             355695238']                                        
                    INFO     Combining to Movie file.   scene_file_writer.py:597
                    DEBUG    Partial movie files to     scene_file_writer.py:538
                             combine (2 files): ['/User                         
                             s/uname/python/test                         
                             /media/videos/test                         
                             /480p15/partial_movie_file                         
                             s/Test/3163782288_96663841                         
                             1_2358810818.mp4', '/Users                         
                             /uname/python/test                        
                             /media/videos/test/                         
                             480p15/partial_movie_files                         
                             /Test/2201830969_337534178                         
                             0_1355695238.mp4']                                 
[05/07/22 06:08:27] INFO                                scene_file_writer.py:718
                             File ready at '/Users/uname                       
                             /python/test/me                         
                             dia/videos/test/480p1                         
                             5/Test_ManimCE_v0.15.2.gif                         
                             '                                                  
                                                                                
                    INFO     Rendered Test                          scene.py:240
                             Played 2 animations                                
                    INFO     Previewed File at: '/Users/uname       file_ops.py:213
                             /python/test/media/videos/test            
                             /480p15/Test_ManimCE_v0.15.2                
                             .gif'                                              

System specifications

System Details

• OS (with version, e.g., Windows 10 v2004 or macOS 10.15 (Catalina)): macOS 12.3.1
• RAM: 8GB
• Python version (python/py/python3 --version): 3.10.0
• Installed modules (provide output from pip list):

Package                   Version
------------------------- -----------
backports.cached-property 1.0.1
certifi                   2021.10.8
charset-normalizer        2.0.12
click                     8.0.4
click-default-group       1.2.2
cloup                     0.13.0
colour                    0.1.5
commonmark                0.9.1
Cython                    0.29.28
decorator                 5.1.1
glcontext                 2.3.5
idna                      3.3
isosurfaces               0.1.0
manim                     0.15.2
ManimPango                0.4.0.post2
mapbox-earcut             0.12.11
moderngl                  5.6.4
moderngl-window           2.4.1
multipledispatch          0.6.0
networkx                  2.7.1
numpy                     1.22.2
Pillow                    9.0.1
pip                       22.0.4
pycairo                   1.21.0
pydub                     0.25.1
pyglet                    1.5.23
Pygments                  2.11.2
pyobjc-core               8.4.1
pyobjc-framework-Cocoa    8.4.1
pyrr                      0.10.3
requests                  2.27.1
rich                      12.3.0
scipy                     1.8.0
screeninfo                0.8
setuptools                57.4.0
six                       1.16.0
skia-pathops              0.7.2
srt                       3.5.2
tqdm                      4.63.0
urllib3                   1.26.9
watchdog                  2.1.6

FFMPEG

Output of ffmpeg -version:

ffmpeg version 5.0.1 Copyright (c) 2000-2022 the FFmpeg developers
built with Apple clang version 13.0.0 (clang-1300.0.29.30)
configuration: --prefix=/usr/local/Cellar/ffmpeg/5.0.1 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox
libavutil      57. 17.100 / 57. 17.100
libavcodec     59. 18.100 / 59. 18.100
libavformat    59. 16.100 / 59. 16.100
libavdevice    59.  4.100 / 59.  4.100
libavfilter     8. 24.100 /  8. 24.100
libswscale      6.  4.100 /  6.  4.100
libswresample   4.  3.100 /  4.  3.100
libpostproc    56.  3.100 / 56.  3.100```
</details>

[behackl]

Thank you for your report! I just investigated a bit: The reason why this happens is due to the, admittedly, very strange way of AnimationGroup of handling a change of run_time. Instead of rewriting the animation timing table (in the anims_with_timings attribute) when the global runtime of an AnimationGroup is changed, the time in AnimationGroup.interpolate is scaled using the original run time determined at initialization.

While Succession inherits from AnimationGroup, it overrides interpolate and uses its own mechanism which scales the time with the specified run_time (which does not necessarily fit to the timings determined initially).

I see three possible ways of resolving this:

1. The implementation is changed in the spirit of the solution in AnimationGroup and the time in Succession.interpolate should be scaled with the (initially determined) end time of the final animation, or
2. We change the way timings in anims_with_timings are stored to be independent of the animation run length, everything should be made relative, or
3. We turn run_time into a property of AnimationGroup whose setter recomputes the anims_with_timings attribute, then the time in interpolate can be scaled with self.run_time in any instance.

To be fair, there is a fourth solution as well: getting rid of Succession entirely because it is (or at least should be) just a glorified version of AnimationGroup with lag_ratio defaulting to 1. Looking at the code, I'm somewhat sure that lag_ratio smaller than 1 breaks the implementation anyways (there is always only exactly one active animation). I can remember there were some special cases where Succession behaved nicer than AnimationGroup, but perhaps these have been fixed in the meantime...