Cannot find FFmpeg DLLs by default

[aboood40091]

🐛 Describe the bug

Continuing from #912 as the underlying issue has not been fixed.
The issue is that torchcodec is not able to find FFmpeg DLLs, even if the FFmpeg bin folder is added to PATH.

Sample of the error:

[start of libtorchcodec loading traceback]
FFmpeg version 7: Could not find module 'C:\Python313\site-packages\torchcodec\libtorchcodec_core7.dll' (or one of its dependencies). Try using the full path with constructor syntax.
FFmpeg version 6: Could not find module 'C:\Python313\site-packages\torchcodec\libtorchcodec_core6.dll' (or one of its dependencies). Try using the full path with constructor syntax.
FFmpeg version 5: Could not find module 'C:\Python313\site-packages\torchcodec\libtorchcodec_core5.dll' (or one of its dependencies). Try using the full path with constructor syntax.
FFmpeg version 4: Could not find module 'C:\Python313\site-packages\torchcodec\libtorchcodec_core4.dll' (or one of its dependencies). Try using the full path with constructor syntax.
[end of libtorchcodec loading traceback].

Currently, one fix, as recommended in this French comment, is to directly copy the DLLs into the torchcodec site-packages folder.

Versions

Using torch 2.8+cu128, torchcodec 0.7, and Python 3.13.

[Yozer]

Similar issue but for me it wasn't finding nppicc64_12.dll
I don't have it in my venv (pytorch 2.9.1 + 12.8 cuda).

import os
os.add_dll_directory(r"C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v12.8\bin")

doing this fixed problem

[aboood40091]

#1006 seems to be related, but they said they're using torch 2.9 and it works for them on 2.8.
However, I can confirm that the issue is there on 2.8 on my side, and it's specifically because torchcodec cannot find FFmpeg DLLs even if its bin folder is in PATH, and copying the DLLs directly to the torchcodec immediately fixes the problem.

Also seems to be a duplicate of #1014, but it was hard to determine with that title... (The issue is currently literally titled, "python windows 3.8 +")

But yes, this seems to be an explicit change in Python 3.8:
https://docs.python.org/3/whatsnew/3.8.html#bpo-36085-whatsnew

[aboood40091]

Submitted a pull request to fix the issue: #1109.