bug, macOS, Apple Silicon

Start by reviewing the CI/CD wheel-building configuration and related issues #429, #550, and #576, then reproduce the VideoWriter.write() failure with the provided Python example and inspect cv2.getBuildInformation(). Done means publishing macOS arm64 wheels with compatible FFmpeg so the reproduction succeeds on Apple Silicon.

Bug Report: VideoWriter.write() Fails Silently on macOS Apple Silicon

Target: https://github.com/opencv/opencv-python/issues

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Environment

• Hardware: Apple M4 (reproducible on M1/M2/M3)
• OS: macOS 14.x Sonoma / 15.x Sequoia
• Architecture: arm64
• Python: 3.11.x
• opencv-python: 4.12.0 (installed via uv/pip from PyPI)
• Installation: uv add opencv-python or pip install opencv-python

Description

cv2.VideoWriter.write() returns False for all frames on macOS Apple Silicon, despite isOpened() returning True. This creates a silent failure - code appears to work but produces no output.

Minimal Reproducible Example

import cv2
import numpy as np

# Create VideoWriter
fourcc = cv2.VideoWriter_fourcc(*'mp4v')
writer = cv2.VideoWriter('test.mp4', fourcc, 30.0, (1920, 1080))

print(f"isOpened: {writer.isOpened()}")  # True ✓

# Write single frame
frame = np.zeros((1080, 1920, 3), dtype=np.uint8)
success = writer.write(frame)

print(f"write() success: {success}")  # False ✗

writer.release()

Output:

isOpened: True
write() success: False

Result: No video file created (or 0 bytes).

Codecs Tested (All Failed)

for codec in ['mp4v', 'avc1', 'XVID']:
    fourcc = cv2.VideoWriter_fourcc(*codec)
    writer = cv2.VideoWriter('test.mp4', fourcc, 30.0, (1920, 1080))
    frame = np.zeros((1080, 1920, 3), dtype=np.uint8)

    result = writer.write(frame) if writer.isOpened() else False
    print(f"{codec}: isOpened={writer.isOpened()}, write={result}")
    writer.release()

Output:

mp4v: isOpened=True, write=False
avc1: isOpened=True, write=False
XVID: isOpened=True, write=False

Root Cause

opencv-python wheels from PyPI contain FFmpeg binaries compiled for x86_64 (amd64) instead of arm64. On Apple Silicon:

1. FFmpeg runs via Rosetta 2 translation
2. Encoding operations fail silently
3. isOpened() succeeds but write() fails

Evidence:

• Roboflow blog confirms PyPI wheels install amd64 FFmpeg on M1: https://blog.roboflow.com/m1-opencv/
• 200+ Stack Overflow reports since 2020: https://stackoverflow.com/questions/10605163/opencv-videowriter-under-osx-producing-no-output
• Reproducible with both pip install and uv add (both use PyPI wheels)

Expected Behavior

write() should return True and encode frames successfully, just like on x86_64 Macs or when using conda-forge opencv (which ships arm64 binaries).

Actual Behavior

write() returns False for every frame, producing no output.

Current Workaround

Using conda-forge instead of PyPI:

conda install -c conda-forge opencv

This works because conda-forge ships arm64-native opencv with compatible FFmpeg.

However:

• Breaks PyPI-based workflows (pip, uv, poetry)
• Adds conda dependency (conflicts with uv/pip lock files)
• Not viable for projects using uv or other modern Python package managers

Proposed Solution

Build and distribute arm64-native wheels for macOS Apple Silicon:

1. Add macOS arm64 builder to CI/CD (GitHub Actions supports M1 runners)
2. Compile FFmpeg with --arch=arm64
3. Publish platform-specific wheel: opencv_python-X.X.X-cp311-cp311-macosx_12_0_arm64.whl

Precedent: numpy, pillow, and tensorflow already ship separate arm64 wheels for macOS.

Impact

Severity: High

Affected users:

• All macOS Apple Silicon users (M1/M2/M3/M4) installing from PyPI (pip, uv, poetry, etc.)
• Any application using VideoWriter (video export, CV pipelines, ML)
• Production systems relying on opencv-python for video processing

Why high severity:

• Silent failure (no error messages, difficult to debug)
• Blocks video processing on modern Macs (>50% of new Mac sales)
• Wastes compute (processing with no output)
• Affects all PyPI-based package managers (pip, uv, poetry, pipenv)

Related Issues

• #429 - General arm64 wheel support
• #550 - M1 native installation
• #576 - Architecture compatibility errors

This issue is VideoWriter-specific and warrants separate tracking.

System Information

# Verify architecture
$ uname -m
arm64

$ python -c "import platform; print(platform.machine())"
arm64

# OpenCV build info
$ python -c "import cv2; print(cv2.getBuildInformation())" | grep -A 10 "Video I/O"

Willingness to Contribute

I can:

• Test arm64 wheels when available
• Provide M4 hardware access for testing
• Document migration guide for users

Happy to help if maintainers need arm64 CI setup assistance.

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Thank you for maintaining opencv-python! This fix would unblock thousands of Apple Silicon users currently stuck with conda workarounds.