[Python] PyQt6: Unwanted Bounding Box Around My Round Button Overlay On Top Of VLC Video Widget

I'm trying to put a round button on top of a playing video (VLC video widget). I'm using PyQt6. The round button displays fine before the video is playing. But, once the video starts to play, Qt adds a bounding box around my round button. One suboptimal option is to use a circular clipping mask. But the round button will have jagged edge since the mask is binary. I've tried many suggested solutions and still unable to get rid of the box around my round button. I made a minimal demo of what I have tried below. Instead of QPushbutton, I made a QWidget that draws a simple circle. The problem is the same: can't get rid of the black box around the circle.

enter image description here

import vlc
import sys
from PyQt6.QtWidgets import QApplication, QMainWindow, QWidget
from PyQt6.QtCore import Qt, QRectF
from PyQt6.QtGui import QPainter, QColor, QBrush, QPen

# --- Circle Widget ---
class CircleWidget(QWidget):
def __init__(self, parent=None, diameter=100, color=QColor(255, 0, 0, 128)): # Red, 50% transparent
super().__init__(parent)
self.diameter = diameter
self.color = color
self.setFixedSize(diameter, diameter)

# self.setAttribute(Qt.WidgetAttribute.WA_TranslucentBackground, True)
self.setAttribute(Qt.WidgetAttribute.WA_StyledBackground, True)
self.setAutoFillBackground(False)
self.setWindowFlags(Qt.WindowType.FramelessWindowHint)
self.setAttribute(Qt.WidgetAttribute.WA_NoSystemBackground, True)

self.setStyleSheet("background: transparent; border: none;")

def paintEvent(self, event):
painter = QPainter(self)
painter.setRenderHint(QPainter.RenderHint.Antialiasing)
painter.setBrush(QBrush(self.color))
painter.setPen(QPen(Qt.PenStyle.NoPen))
painter.drawEllipse(QRectF(self.rect()))
# -------------------------------------

VIDEO_PATH = r"D:\test.mp4"

app = QApplication(sys.argv)
main_window = QMainWindow()
main_window.setWindowTitle("PyQt6 VLC Sibling Overlay Test")
main_window.setGeometry(100, 100, 640, 480)

main_container = QWidget()
main_window.setCentralWidget(main_container)

# Video Output Widget (Child of container)
video_widget = QWidget(parent=main_container)
video_widget.setStyleSheet("background-color: black;")

# Overlay the Circle on top of the video
circle_overlay = CircleWidget(parent=main_container)

player = None
instance = None

try:
instance = vlc.Instance()
player = instance.media_player_new()
media = instance.media_new_path(VIDEO_PATH) # any video file
player.set_media(media)

main_window.show()
QApplication.processEvents()

video_widget.setGeometry(main_container.rect())

# Position the circle in the container
overlay_x = 80
overlay_y = 80
circle_overlay.move(overlay_x, overlay_y)
circle_overlay.show()
circle_overlay.raise_() # Ensure it's visually on top of video

win_id = video_widget.winId()
if sys.platform.startswith('win'):
player.set_hwnd(win_id)
print(f"Set HWND to {win_id}")
else:
print(f"Warning: Platform specific VLC output binding not implemented for {sys.platform}")

# --- Play Video ---
play_result = player.play()
if play_result != 0:
print("Error: Failed to start playback.")
sys.exit(1)

status = app.exec()

except Exception as e:
print(f"An error occurred: {e}")

finally:
player.stop()


Any help would be much appreciated!

I just need to display a clean round button over the video playing in the background.

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