Branch

main branch (1.x version, such as v1.0.0, or dev-1.x branch)

Prerequisite

• I have searched Issues and Discussions but cannot get the expected help.
• I have read the documentation but cannot get the expected help.
• The bug has not been fixed in the latest version.

Environment

OS: macOS (arm64, Apple Silicon M-series chip)
Python Version: 3.8 (managed via Conda)
Target Project: MMAction2
Problematic Dependency: decord

Describe the bug

Hi MMAction2 Team and Community,

I recently went through the process of installing MMAction2 on a macOS arm64 (Apple Silicon) machine and encountered significant difficulties with the decord dependency. Standard installation methods via pip or conda for decord failed on this platform.

After extensive troubleshooting, I found a viable solution that involves using the eva-decord fork and specific versions of dependencies. I'm sharing this detailed process here to help other users facing similar issues and potentially to inform future documentation Verbesserungen.

Problem Summary:
The primary issue was that pip could not find a suitable distribution for decord because:

1. The PyPI JSON Simple API for decord did not list any source distributions (.tar.gz).
2. No pre-compiled decord wheels for osx-arm64 were available on PyPI.
3. Mainstream Conda channels (dmlc, conda-forge) also lacked osx-arm64 packages for decord.
4. Compiling the original dmlc/decord from source failed due to API incompatibilities with the latest FFmpeg (7.x).

Environment:

• OS: macOS (arm64, Apple Silicon M-series chip)
• Python Version: 3.8 (managed via Conda)
• Target Project: MMAction2
• Problematic Dependency: decord

Problem Description:
Attempting to install MMAction2 on a macOS arm64 system via pip install -v -e . failed because its dependency decord>=0.4.1 could not be satisfied. The error message was ERROR: Could not find a version that satisfies the requirement decord>=0.4.1 (from mmaction2) (from versions: none).

Troubleshooting and Resolution Process:

1. Initial Diagnosis: pip Fails to Find decord

   • Attempts with pip install "decord>=0.4.1" -v and pip index versions decord both reported no matching distribution.
   • curl -v https://pypi.org/simple/decord/ confirmed that network connectivity to PyPI Simple Index (HTML format) was working and contained entries for decord.
   • However, curl -H "Accept: application/vnd.pypi.simple.v1+json" https://pypi.org/simple/decord/ revealed that the JSON Simple API response from PyPI did not list any source distributions (.tar.gz) for decord; it only listed wheel files. This was identified as the root cause for pip not finding a source package to compile, even with the --no-binary :all: flag.

2. Attempting Conda Installation of decord

   • conda install -c dmlc decord failed with PackagesNotFoundError (no osx-arm64 package in the dmlc channel).
   • conda install -c conda-forge decord also failed with PackagesNotFoundError (no osx-arm64 package in the conda-forge channel).
   • Conclusion: At the time, mainstream Conda channels did not provide pre-compiled decord packages for osx-arm64.

3. Attempting to Build Original dmlc/decord from Source

   • Cloned the repository: git clone --recursive https://github.com/dmlc/decord.git.
   • Installed build dependencies: Xcode Command Line Tools, Homebrew, and then brew install cmake ffmpeg libomp.
     • An initial network issue (Could not resolve host: github.com) was resolved by fixing local network/DNS settings.
   • Build Failure: When attempting to compile with the latest FFmpeg installed via Homebrew (version 7.x at the time), cmake could find FFmpeg, but the make stage failed with compilation errors related to symbols like AVBSFContext and av_bsf_free, which had changed in newer FFmpeg APIs. This indicated an incompatibility between the original decord source code and FFmpeg 7.x.

4. Switching to the eva-decord Fork

   • Based on a suggestion, switched to the georgia-tech-db/eva-decord fork (https://github.com/georgia-tech-db/eva-decord), which claimed support for Apple Silicon and newer FFmpeg versions (5.x, 6.x).
   • Cloned the fork: git clone --recursive https://github.com/georgia-tech-db/eva-decord.git.

5. Adjusting FFmpeg Version for eva-decord Compatibility

   • An initial attempt to compile eva-decord with FFmpeg 7.x resulted in cmake success, but make failed during the compilation of src/audio/audio_reader.cc. Errors indicated missing members like channels in AVCodecParameters and channel_layout in AVFrame, pointing to an API incompatibility between eva-decord (primarily supporting up to FFmpeg 6.x) and FFmpeg 7.x.
   • Solution: Downgrade FFmpeg.
     • Uninstalled FFmpeg 7.x: brew uninstall ffmpeg
     • Installed FFmpeg 6.x (Homebrew provided an ffmpeg@6 package): brew install ffmpeg@6 (which installed version 6.1.2_10).
     • Updated the PKG_CONFIG_PATH environment variable to point to the pkgconfig directory of the newly installed ffmpeg@6:

       unset PKG_CONFIG_PATH
       export PKG_CONFIG_PATH="$(brew --prefix ffmpeg@6)/lib/pkgconfig:$PKG_CONFIG_PATH"

6. Building and Installing eva-decord

   • In the eva-decord source directory, compiled using the downgraded FFmpeg 6.x:

     cd eva-decord
     rm -rf build
     mkdir build && cd build
     cmake .. -DUSE_CUDA=OFF -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=${CONDA_PREFIX} 
     make -j8 # or make

     The compilation process showed several warnings about deprecated FFmpeg APIs but no errors, eventually succeeding with [100%] Built target decord. The C++ core library was successfully built.
   • Installing Python Bindings - Crucial Step:
     • An initial pip install . from the eva-decord root directory failed, as setup.py was not present there.
     • Identified Issue: After successfully building and installing eva-decord (from its python/ subdirectory), pip list showed the package name as eva-decord, not decord. This would cause MMAction2's dependency resolver to fail.
     • Solution:
       1. Navigate to the eva-decord/python/ directory.
       2. Edit the setup.py file. Modify the name parameter in the setup() function call from name='eva-decord' to name='decord'.
       3. Save setup.py.
       4. Uninstall any previously installed versions of eva-decord or decord:

          pip uninstall eva-decord -y
          pip uninstall decord -y 

       5. In the eva-decord/python/ directory, reinstall using the modified setup.py:

          pip install . -vvv

     • Verification: pip list | grep decord then showed decord 0.6.0. In Python, import decord; print(decord.__name__, decord.__version__) confirmed decord 0.6.0.

7. Installing MMAction2

   • Navigated back to the mmaction2 source directory.
   • Executed pip install -v -e ..
   • Success! The MMAction2 dependency resolver found the installed decord 0.6.0 package and proceeded to install MMAction2 and its other dependencies successfully.

Summary and Recommendations:

• Resolving the decord dependency for projects like MMAction2 on macOS arm64 can be challenging due to the lack of official source distributions (sdist) on PyPI and limited arm64 support in Conda channels for decord.
• The georgia-tech-db/eva-decord fork serves as a viable alternative, offering better support for Apple Silicon and more recent FFmpeg versions.
• Ensuring FFmpeg version compatibility is crucial when building eva-decord (or the original decord) from source. Current experience suggests FFmpeg 6.x (e.g., ffmpeg@6 from Homebrew) works well with eva-decord.
• Key Fix: If using a decord fork that uses a different package name in its setup.py (like eva-decord), it's necessary to modify its name parameter to decord. This allows projects like MMAction2, which depend on the standard decord package name, to correctly identify the dependency.
• Correctly setting the PKG_CONFIG_PATH environment variable to point to the lib/pkgconfig directory of the chosen FFmpeg version is essential for CMake to locate the FFmpeg libraries.

Hopefully, this report will assist other developers facing similar challenges on macOS arm64.

Reproduces the problem - code sample

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Reproduces the problem - command or script

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Reproduces the problem - error message

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Additional information

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