[BUG] Black screen on macOS

[albertocasagrande]

Terms

• Checked the existing issues and discussions to see if my issue had not already been reported;
• Checked the frequently asked questions;
• Read the installation instructions;
• Created a virtual environment in which I can reproduce my bug;

Describe the issue

The command manim-slides present shows a black screen on macOS. I was not able to reproduce the issue on Ubuntu 20.04.

Unlike #315 and #377, the issue cannot be mitigated by using the option --hide-info-window and no debug messages are reported

When the info window is active, it correctly reports the number of the slides. Thus, manim-slides seems to properly read the JSON file. The arrow keys move the presentation back and forth as expected, but no video plays.

Reproducibility

After rendering the basic example available on the main page of the GitHub repository, the command manim-slides BasicExample shows the presentation window with a black background.

Issue cause

The qtpy method QMediaPlayer.setSource() misinterprets relative paths on macOS. Thus, this seems to be a qtpy issue. However, there is a small fix that solves the issue on manim-slides (see below).

Command

manim-slides BasicExample

Issue Type

Visual bug when presenting (manim-slides present)

Python version

Python 3.14.0

Python environment

Manim Slides version: 5.5.2
Python executable: /opt/homebrew/Cellar/manim-slides/5.5.2/libexec/bin/python
Manim bindings:
/opt/homebrew/Cellar/manim-slides/5.5.2/libexec/lib/python3.14/site-packages/pydub/utils.py:300: SyntaxWarning: "\(" is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\\("? A raw string is also an option.
  m = re.match('([su]([0-9]{1,2})p?) \(([0-9]{1,2}) bit\)$', token)
/opt/homebrew/Cellar/manim-slides/5.5.2/libexec/lib/python3.14/site-packages/pydub/utils.py:301: SyntaxWarning: "\(" is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\\("? A raw string is also an option.
  m2 = re.match('([su]([0-9]{1,2})p?)( \(default\))?$', token)
/opt/homebrew/Cellar/manim-slides/5.5.2/libexec/lib/python3.14/site-packages/pydub/utils.py:310: SyntaxWarning: "\(" is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\\("? A raw string is also an option.
  elif re.match('(flt)p?( \(default\))?$', token):
/opt/homebrew/Cellar/manim-slides/5.5.2/libexec/lib/python3.14/site-packages/pydub/utils.py:314: SyntaxWarning: "\(" is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\\("? A raw string is also an option.
  elif re.match('(dbl)p?( \(default\))?$', token):
        manim (version: 0.19.0)
        manimgl not found
Qt API: pyqt6 (version: 6.9.3)

What is your platform?

macOS

Other platform

No response

Manim Slides Python code

from manim import *  # or: from manimlib import *

from manim_slides import Slide


class BasicExample(Slide):
    def construct(self):
        circle = Circle(radius=3, color=BLUE)
        dot = Dot()

        self.play(GrowFromCenter(circle))
        self.next_slide()  # Waits user to press continue to go to the next slide

        self.next_slide(loop=True)  # Start loop
        self.play(MoveAlongPath(dot, circle), run_time=2, rate_func=linear)
        self.next_slide()  # This will start a new non-looping slide

        self.play(dot.animate.move_to(ORIGIN))

Relevant log output

Screenshots

Additional information

No response

Recommended fix or suggestions

Either waiting for a qtpy fix or using the absolute paths of the video in place of the relative paths. In particular, any line of the type QUrl.fromLocalFile(str(...)) should become QUrl.fromLocalFile(os.path.abspath(...)).

The following patch solves the issue.

issue.patch

[jeertmans]

Hi @albertocasagrande, thanks for reporting this issue! Unfortunately, I do not have any macOS computer, so I have to blindly trust you on this. While it makes sense that using relative paths could be an issue, I am not sure the fix is the most appropriate one. Could you provide a bit more information about this bug?

First, you suggested

waiting for a qtpy fix

but I don't think that's qtpy's fault, because it re-exports from PySide6 or PyQt6, and does not seem to redefine QtCore.QUrl. So, did you try with PySide6 instead?

Next, how did you find that the issue came from the path? Did you have any error in the console from Qt complaining about this? If so, could you include it too?

Finally, I wonder if the bug is related to the path being wrong, or if the QUrl.fromLocalFile method simply does not accept relative path? Could you maybe print out the following?

f = str(...)  # Replace with actual path
print(f)
url = QUrl.fromLocalFile(str(...))
print(url)

If you have both macOS an and Linux, the best would be to show the output in both cases. Otherwise, I can test on Linux myself.

Thanks in advance!

[albertocasagrande]

but I don't think that's qtpy's fault, because it re-exports from PySide6 or PyQt6, and does not seem to redefine QtCore.QUrl. So, did you try with PySide6 instead?

I tried both PyQt6 (with Python 3.14) and PySide6 (with Python 3.13) on macOS, and they both have the same problem.
On Linux, neither of the two exhibits the issue.

Next, how did you find that the issue came from the path?

By reverse engineering the code of present/player.py. My doubt was about wrong video URLs because the JSON was properly read. So, I tried to print self.current_file in method load_current_media(). Everything was fine, so I tried to replace self.current_file with a constant (relative) path to a video in line 392

           url = QUrl.fromLocalFile(str(self.current_file))

This change did not solve the issue. Since the core part of the player code involves at most 5 lines and all of them were good, I tried the absolute path, and it worked.

Did you have any error in the console from Qt complaining about this? If so, could you include it too?

None. Not even using -v DEBUG

Finally, I wonder if the bug is related to the path being wrong, or if the QUrl.fromLocalFile method simply does not accept relative path? Could you maybe print out the following?

f = str(...) # Replace with actual path
print(f)
url = QUrl.fromLocalFile(str(...))
print(url)

I tested it before the bug report and, as I wrote above, everything was fine: the first print line prints the proper video in slides/files/BasicExample/; the second print line prints file:<relative path to the video>. I am not an expert in Qt, but as far as I understand, everything seems consistent with the documentation.

If you have both macOS an and Linux, the best would be to show the output in both cases. Otherwise, I can test on Linux myself.

macOS

slides/files/BasicExample/361b52b4f6bd21034597993bda27b41b79817c663f586243d063835f9b0998b0.mp4
PyQt6.QtCore.QUrl('file:slides/files/BasicExample/361b52b4f6bd21034597993bda27b41b79817c663f586243d063835f9b0998b0.mp4')

Ubuntu

slides/files/BasicExample/361b52b4f6bd21034597993bda27b41b79817c663f586243d063835f9b0998b0.mp4
PySide6.QtCore.QUrl('file:slides/files/BasicExample/361b52b4f6bd21034597993bda27b41b79817c663f586243d063835f9b0998b0.mp4')

[jeertmans]

Thank you for the very detailed report! After reading a bit on forums, it looks like they all recommend to work with absolute paths when using Qt.

So I think your patch is good. But I prefer using str(path.resolve(strict=True)) as we use pathlib.Path, and not the old os.path module. Using resolve could also prevent possible issue with symlinks.

Could you make a PR for this? (I.e., replacing the two occurrences of QUrl.fromLocalFile(str(<path>)) with QUrl.fromLocalFile(str(<path>.resolve(strict=True))).)