Expose TorchCodecConfig.cmake

[dvrogozh]

This commit exposes torchcodec core library to be used by third party modules on the C++ level. The primary purpose is to allow non-CUDA device interfaces out-of-tree implementations. There are the following major changes:

• Exposed TorchCodecConfig.cmake which defines torchcodec targets to be linked with

• Provided Python level APIs to faciliate out-of-tree device interfaces work with torchcodec:

  • torchcodec.cmake_prefix_path - path which points to TorchCodecConfig.cmake configuration
  • torchcodec.variant - variant of the torchcodec library which was loaded, i.e. N in libtorchcodec_core{N}.so (currently ffmpeg_major_version)
  • torchcodec.core_library_path - full path of the loaded torchcodec core library

• src/torchcodec/_core/ dropped from include paths to allow using of the core library out-of-tree

TorchCodecConfig.cmake has 2 working modes:

• By default config works by checking available version of FFmpeg libraries via pkg-config and configures corresponding (single) version of torchcodec
• Altenatively, if TORCHCODEC_FFMPEG{N}_INSTALL_PREFIX is set (N=4,5,6,7 - version of FFmpeg), then config defines torchcodec target corresponding to the specified FFmpeg version. Note that multiple prefixes can be specified at the same time allowing to build against few torchcodec versions at once.

Config will define TORCHCODEC_VARIANTS variable with value corresponding to FFmpeg major versions of available torchcodec core libraries. Further, config will also define torchcodec::ffmpeg${N} and torchcodec::core${N} targets where N takes values from TORCHCODEC_VARIANTS.

See the following repository for an actual out-of-tree device interface torchcodec plugin:

• https://github.com/dvrogozh/torchcodec-xpu

I suggest to pay attention on these:

• https://github.com/dvrogozh/torchcodec-xpu/blob/59bfef60e9b41244e804c112729c42d9176ae368/src/torchcodec_xpu/__init__.py#L44 for plugin ;loading in respect to the loaded torchcodec library
• https://github.com/dvrogozh/torchcodec-xpu/blob/59bfef60e9b41244e804c112729c42d9176ae368/src/torchcodec_xpu/CMakeLists.txt#L81 for building multiple plugin targets depending on the available ffmpeg and torchcodec versions

CC: @scotts, @NicolasHug

[NicolasHug]

Thanks @dvrogozh , I left some questions and some comments below. It looks good overal, but I hope we can simplify and unify the logic with the one that already exists within our own cmake files.

On the #include path changes, I will have to pre-import your PR internall to verify that this isn't breaking our internal build (and to try to find internal workarounds if needed).

[NicolasHug]

Can you help me understand why in

https://github.com/dvrogozh/torchcodec-xpu/blob/59bfef60e9b41244e804c112729c42d9176ae368/src/torchcodec_xpu/__init__.py#L43

we only need to load the libtorchcodec_core?.so file, and not the other .so like libtorchcodec_pybind_ops?.so and libtorchcodec_custom_ops?.so

[NicolasHug]

Same here, the logic in this whole branch should ideally be unified with

torchcodec/src/torchcodec/_core/CMakeLists.txt

Lines 276 to 315 in 75a3325

	else()
	message(
	STATUS
	"Building and dynamically linking libtorchcodec against the installed
	FFmpeg libraries. This require pkg-config to be installed. If you have
	installed FFmpeg from conda, make sure pkg-config is installed from
	conda as well."
	)
	find_package(PkgConfig REQUIRED)
	pkg_check_modules(LIBAV REQUIRED IMPORTED_TARGET
	libavdevice
	libavfilter
	libavformat
	libavcodec
	libavutil
	libswresample
	libswscale
	)
	# Split libavcodec's version string by '.' and convert it to a list
	string(REPLACE "." ";" libavcodec_version_list ${LIBAV_libavcodec_VERSION})
	# Get the first element of the list, which is the major version
	list(GET libavcodec_version_list 0 libavcodec_major_version)
	if (${libavcodec_major_version} STREQUAL "58")
	set(ffmpeg_major_version "4")
	elseif (${libavcodec_major_version} STREQUAL "59")
	set(ffmpeg_major_version "5")
	elseif (${libavcodec_major_version} STREQUAL "60")
	set(ffmpeg_major_version "6")
	elseif (${libavcodec_major_version} STREQUAL "61")
	set(ffmpeg_major_version "7")
	elseif (${libavcodec_major_version} STREQUAL "62")
	set(ffmpeg_major_version "8")
	else()
	message(
	FATAL_ERROR
	"Unsupported libavcodec version: ${libavcodec_major_version}"
	)
	endif()

[dvrogozh]

Ok, I've missed this one. I will need to look into it.

[dvrogozh]

On the #include path changes, I will have to pre-import your PR internall to verify that this isn't breaking our internal build (and to try to find internal workarounds if needed).

I've rebased the PR and resolved conflicts, but I will take a look and start address review comments later today or early next week. Please, let me know how #include story goes. If this change is ok (I hope so), then we may consider to make it separately to reduce the scope of this PR and simplify/focus review on the cmake aspects.

[meta-codesync]

@NicolasHug has imported this pull request. If you are a Meta employee, you can view this in D85451979.

[NicolasHug]

Can confirm the header #include changes are OK internally! Yes, happy to consider a separate diff that does just that. Thank you!

[dvrogozh]

Can confirm the header #include changes are OK internally! Yes, happy to consider a separate diff that does just that.

Thank you! Here is includes PR: #1002.