Expose TorchCodecConfig.cmake

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`.

Signed-off-by: Dmitry Rogozhkin <dmitry.v.rogozhkin@gmail.com>

Author: Dmitry Rogozhkin

src/torchcodec/__init__.py

@@ -4,8 +4,11 @@
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
 
+import os.path as _osp
+
 # Note: usort wants to put Frame and FrameBatch after decoders and samplers,
 # but that results in circular import.
+from ._core import core_library_path, variant
 from ._frame import AudioSamples, Frame, FrameBatch  # usort:skip # noqa
 from . import decoders, samplers  # noqa
 
@@ -14,3 +17,5 @@
     from .version import __version__  # noqa: F401
 except Exception:
     pass
+
+cmake_prefix_path = _osp.join(_osp.dirname(__file__), "share", "cmake")

src/torchcodec/_core/AVIOContextHolder.cpp

@@ -4,7 +4,7 @@
 // This source code is licensed under the BSD-style license found in the
 // LICENSE file in the root directory of this source tree.
 
-#include "src/torchcodec/_core/AVIOContextHolder.h"
+#include "AVIOContextHolder.h"
 #include <torch/types.h>
 
 namespace facebook::torchcodec {

src/torchcodec/_core/AVIOContextHolder.h

@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include "src/torchcodec/_core/FFMPEGCommon.h"
+#include "FFMPEGCommon.h"
 
 namespace facebook::torchcodec {
 

src/torchcodec/_core/AVIOFileLikeContext.cpp

@@ -4,7 +4,7 @@
 // This source code is licensed under the BSD-style license found in the
 // LICENSE file in the root directory of this source tree.
 
-#include "src/torchcodec/_core/AVIOFileLikeContext.h"
+#include "AVIOFileLikeContext.h"
 #include <torch/types.h>
 
 namespace facebook::torchcodec {

src/torchcodec/_core/AVIOFileLikeContext.h

@@ -9,7 +9,7 @@
 #include <pybind11/pybind11.h>
 #include <pybind11/stl.h>
 
-#include "src/torchcodec/_core/AVIOContextHolder.h"
+#include "AVIOContextHolder.h"
 
 namespace py = pybind11;
 

src/torchcodec/_core/AVIOTensorContext.cpp

@@ -4,7 +4,7 @@
 // This source code is licensed under the BSD-style license found in the
 // LICENSE file in the root directory of this source tree.
 
-#include "src/torchcodec/_core/AVIOTensorContext.h"
+#include "AVIOTensorContext.h"
 #include <torch/types.h>
 
 namespace facebook::torchcodec {

src/torchcodec/_core/AVIOTensorContext.h

@@ -7,7 +7,7 @@
 #pragma once
 
 #include <torch/types.h>
-#include "src/torchcodec/_core/AVIOContextHolder.h"
+#include "AVIOContextHolder.h"
 
 namespace facebook::torchcodec {
 

src/torchcodec/_core/BetaCudaDeviceInterface.h

@@ -15,11 +15,11 @@
 
 #pragma once
 
-#include "src/torchcodec/_core/CUDACommon.h"
-#include "src/torchcodec/_core/Cache.h"
-#include "src/torchcodec/_core/DeviceInterface.h"
-#include "src/torchcodec/_core/FFMPEGCommon.h"
-#include "src/torchcodec/_core/NVDECCache.h"
+#include "CUDACommon.h"
+#include "Cache.h"
+#include "DeviceInterface.h"
+#include "FFMPEGCommon.h"
+#include "NVDECCache.h"
 
 #include <map>
 #include <memory>
@@ -28,8 +28,8 @@
 #include <unordered_map>
 #include <vector>
 
-#include "src/torchcodec/_core/nvcuvid_include/cuviddec.h"
-#include "src/torchcodec/_core/nvcuvid_include/nvcuvid.h"
+#include "nvcuvid_include/cuviddec.h"
+#include "nvcuvid_include/nvcuvid.h"
 
 namespace facebook::torchcodec {
 

src/torchcodec/_core/CUDACommon.h

@@ -11,9 +11,9 @@
 #include <npp.h>
 #include <torch/types.h>
 
-#include "src/torchcodec/_core/Cache.h"
-#include "src/torchcodec/_core/FFMPEGCommon.h"
-#include "src/torchcodec/_core/Frame.h"
+#include "Cache.h"
+#include "FFMPEGCommon.h"
+#include "Frame.h"
 
 extern "C" {
 #include <libavutil/hwcontext_cuda.h>

src/torchcodec/_core/CpuDeviceInterface.cpp

@@ -4,7 +4,7 @@
 // This source code is licensed under the BSD-style license found in the
 // LICENSE file in the root directory of this source tree.
 
-#include "src/torchcodec/_core/CpuDeviceInterface.h"
+#include "CpuDeviceInterface.h"
 
 namespace facebook::torchcodec {
 namespace {