Move filter graph to stand alone class

[dvrogozh]

Changes:

• Defined stand alone class for the filter graph (based on definition in CpuDeviceInterface)
• Generalized filter graph to:
  • Cover HW backends (by accepting HW frames context)
  • Support configurable filter pipelines (by accepting string pipeline description). For example, it's possible to pass VAAPI or CUDA specific filters:

FiltersContext.filters = "scale=480:270:sws_flags=bilinear"; # for CPU (current usage)
FiltersContext.filters = "scale_vaapi=480:270:format=rgba";  # for VAAPI

These changes will allow:

• Easily define ffmpeg driven decoding + video processing pipeline for any backend supported by ffmpeg (for multi-gpu support)
• Add ffmpeg media filters support to torchcodec (any filter, not only scale or color conversion)

See the following draft PR with the example of using the defined class for ffmpeg-vaapi backend to enable Intel GPU support:

• Full (dec+filters) ffmpeg-vaapi pipeline for Intel GPU (xpu pytorch backend) #832

I believe it can be used as a close reference to implement similar support for ffmpeg-cuda filters (scale_cuda, scale_npp).

CC: @scotts @NicolasHug @eromomon

[dvrogozh]

Pushed a fix for the extra ; typo which was failing some ci checks.

[dvrogozh]

Latest CI errors don't seem to be related with the PR. 2 errors:

Error: Unable to download artifact(s): Artifact not found for name: pytorch_torchcodec__3.9_cu126_x86_64

and

/Users/ec2-user/runner/_work/torchcodec/torchcodec/pytorch/torchcodec/src/torchcodec/_core/custom_ops.cpp:87:47: error: must specify at least one argument for '...' parameter of variadic macro [-Werror,-Wgnu-zero-variadic-macro-arguments]
  TORCH_INTERNAL_ASSERT(tensor.is_contiguous());
                                              ^
/Users/ec2-user/runner/_work/_temp/conda_environment_17164967222/lib/python3.10/site-packages/torch/include/c10/util/Exception.h:425:9: note: macro 'TORCH_INTERNAL_ASSERT' defined here
#define TORCH_INTERNAL_ASSERT(cond, ...)                                         \
* Getting build dependencies for wheel...

I believe the second error is addressed already in #847, so I will need to rebase. Not sure if the first one is addressed. @scotts : should I rebase now or you need time to fix 1st issue?

[dvrogozh]

Rebased on top of latest master. I hope this will help ci to pass as some fixes for ci has recently landed.