Import torchcodec fails, "Could not load this library: libtorchcodec_coreX"

🐛 Describe the bug

Clean install fails on Python 3.10.12 on macOS

mkdir codectest && cd codectest
uv init --python 3.10.12
uv add torch==2.9.1 torchcodec==0.9.1
uv run python -c "import torchcodec"

However, when I use Python 3.11 it succeeds.

Output from importing torchcodec:

/Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torch/_subclasses/functional_tensor.py:279: UserWarning: Failed to initialize NumPy: No module named 'numpy' (Triggered internally at /Users/runner/work/pytorch/pytorch/pytorch/torch/csrc/utils/tensor_numpy.cpp:84.)
  cpu = _conversion_method_template(device=torch.device("cpu"))
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torchcodec/__init__.py", line 12, in <module>
    from . import decoders, encoders, samplers  # noqa
  File "/Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torchcodec/decoders/__init__.py", line 7, in <module>
    from .._core import AudioStreamMetadata, VideoStreamMetadata
  File "/Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torchcodec/_core/__init__.py", line 8, in <module>
    from ._metadata import (
  File "/Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torchcodec/_core/_metadata.py", line 16, in <module>
    from torchcodec._core.ops import (
  File "/Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torchcodec/_core/ops.py", line 104, in <module>
    ffmpeg_major_version, core_library_path = load_torchcodec_shared_libraries()
  File "/Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torchcodec/_core/ops.py", line 75, in load_torchcodec_shared_libraries
    raise RuntimeError(
RuntimeError: Could not load libtorchcodec. Likely causes:
          1. FFmpeg is not properly installed in your environment. We support
             versions 4, 5, 6, 7, and 8. On Windows, ensure you've installed
             the "full-shared" version which ships DLLs.
          2. The PyTorch version (2.9.1) is not compatible with
             this version of TorchCodec. Refer to the version compatibility
             table:
             https://github.com/pytorch/torchcodec?tab=readme-ov-file#installing-torchcodec.
          3. Another runtime dependency; see exceptions below.
        The following exceptions were raised as we tried to load libtorchcodec:

[start of libtorchcodec loading traceback]
FFmpeg version 8: Could not load this library: /Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torchcodec/libtorchcodec_core8.dylib
FFmpeg version 7: Could not load this library: /Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torchcodec/libtorchcodec_core7.dylib
FFmpeg version 6: Could not load this library: /Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torchcodec/libtorchcodec_core6.dylib
FFmpeg version 5: Could not load this library: /Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torchcodec/libtorchcodec_core5.dylib
FFmpeg version 4: Could not load this library: /Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torchcodec/libtorchcodec_core4.dylib
[end of libtorchcodec loading traceback].

Further debugging output:

❯ uv run python
Python 3.10.12 (main, Jul 26 2023, 19:37:41) [Clang 16.0.3 ] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import ctypes
>>> ctypes.CDLL("/Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torchcodec/libtorchcodec_core8.dylib")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/matan/.local/share/uv/python/cpython-3.10.12-macos-aarch64-none/lib/python3.10/ctypes/__init__.py", line 374, in __init__
    self._handle = _dlopen(self._name, mode)
OSError: dlopen(/Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torchcodec/libtorchcodec_core8.dylib, 0x0006): Library not loaded: @rpath/libc10.dylib
  Referenced from: <2BA650F4-E163-3EF6-A721-BAA8124FD98E> /Users/matan/code/codectest/.venv/lib/python3.10/site-packages/torchcodec/libtorchcodec_core8.dylib
  Reason: no LC_RPATH's found

Versions

PyTorch version: 2.9.1
Is debug build: False
CUDA used to build PyTorch: None
ROCM used to build PyTorch: N/A

OS: macOS 15.7.3 (arm64)
GCC version: Could not collect
Clang version: 17.0.0 (clang-1700.4.4.1)
CMake version: version 3.31.6
Libc version: N/A

Python version: 3.10.12 (main, Jul 26 2023, 19:37:41) [Clang 16.0.3 ] (64-bit runtime)
Python platform: macOS-15.7.3-arm64-arm-64bit
Is CUDA available: False
CUDA runtime version: No CUDA
CUDA_MODULE_LOADING set to: N/A
GPU models and configuration: No CUDA
Nvidia driver version: No CUDA
cuDNN version: No CUDA
Is XPU available: False
HIP runtime version: N/A
MIOpen runtime version: N/A
Is XNNPACK available: True
Caching allocator config: N/A

CPU:
Apple M1 Pro

Versions of relevant libraries:
[pip3] Could not collect
[conda] numpy                     1.22.4           py39h7df2422_0    conda-forge

Start with torchcodec/_core/ops.py and reproduce the Python 3.10.12 macOS arm64 setup using the uv commands in the report. Inspect the ctypes loading failure for libtorchcodec_core8.dylib and its missing @rpath/libc10.dylib dependency. Done means the reported clean install imports torchcodec successfully on Python 3.10 while retaining the existing FFmpeg-version loading behavior.