RFE: looping animated PNGs

[Tristan Croll]

The following bug report has been submitted:
Platform:        Linux-6.8.0-59-generic-x86_64-with-glibc2.35
ChimeraX Version: 1.9 (2024-12-11 19:11:19 UTC)
Description
Would it be possible to add an option to `movie encode` to make animated PNGs loop forever? We're being pressured to use Google Slides for all presentations, and it turns out to have remarkably aggravating limitations when it comes to looping video (which I, like many others, use extensively for doing little "rocking" animations to provide depth perception on complex molecular scenes. Problem is, there is no PowerPoint-like mechanism to loop a video - the only option is, during the presentation, to right-click on the playing video and tell it to loop. The only real options available seem to be animated GIF or PNG - but unless they were encoded to loop forever it will only play them once (and if there's a mechanism to replay them, I haven't found it). 

Anyway, I did a quick-and-dirty hack to my personal copy of ChimeraX at https://github.com/RBVI/ChimeraX/blob/1390a711c1b665ffbc53aad80e3f5b12fec07dc2/src/bundles/movie/src/encode.py#L120 to add:

{{{
        if output_format=='apng':
            arg_list.append('-plays')
            arg_list.append('0')
}}}

... which does the trick for me - but I'm sure this is an option that others might appreciate as well.

OpenGL version: 3.3.0 NVIDIA 535.230.02
OpenGL renderer: NVIDIA GeForce RTX 3070/PCIe/SSE2
OpenGL vendor: NVIDIA Corporation

Python: 3.11.4
Locale: en_GB.UTF-8
Qt version: PyQt6 6.7.1, Qt 6.7.1
Qt runtime version: 6.7.3
Qt platform: xcb

XDG_SESSION_TYPE=x11
DESKTOP_SESSION=ubuntu
XDG_SESSION_DESKTOP=ubuntu
XDG_CURRENT_DESKTOP=ubuntu:GNOME
DISPLAY=:1
Manufacturer: Dell Inc.
Model: XPS 8950
OS: Ubuntu 22.04
Architecture: 64bit ELF
Virtual Machine: none
CPU: 20 12th Gen Intel(R) Core(TM) i7-12700
Cache Size: 25600 KB
Memory:
	               total        used        free      shared  buff/cache   available
	Mem:            31Gi        18Gi       4.2Gi       2.0Gi       8.1Gi       9.8Gi
	Swap:          2.0Gi       2.0Gi       0.0Ki

Graphics:
	0000:01:00.0 VGA compatible controller [0300]: NVIDIA Corporation GA104 [GeForce RTX 3070 Lite Hash Rate] [10de:2488] (rev a1)	
	Subsystem: Dell GA104 [GeForce RTX 3070 Lite Hash Rate] [1028:c903]	
	Kernel driver in use: nvidia

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[Tom Goddard]

Should be pretty easy to add a "loopPng true|false|int" option to the emovie encode command. The "-plays" option is only supported by the animated png format (apng).

​https://ffmpeg.org/ffmpeg-formats.html#apng-1

Another idea is to add a more general loop option that takes an integer and uses the ffmpeg -stream_loop <N> which loops the input frames N times. But that makes an N times bigger movie so won't do for infinite looping.

​https://ffmpeg.org/ffmpeg.html#Main-options

[Tristan Croll]

I can see uses for both options - particularly after banging my head
against this more today. An animated PNG takes up ~10x the space of the
equivalent mp4, and it seems Google Slides has some hard limit on how big a
file it will actually animate (not sure exactly where the boundary is -
somewhere between 90 and ~300 frames at 800x600). So in many cases it would
probably actually be just as efficient to simply loop an mp4 10 times.

On Mon, Jun 9, 2025 at 7:46 PM ChimeraX <ChimeraX-bugs-admin@cgl.ucsf.edu>
wrote:

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