Add NvCodecConfig.h, migrate WITH_NVCODEC guards to XPRS_HAS_NVDEC/XPRS_HAS_NVENC

Summary:
This is D1b in the GPU-accelerated H.265 decoding stack for projectaria-tools (plan v11 at ~/gdrive/plans/2026-04-03-gpu-accelerated-h265-decoding-pat-v11.md, tech design at https://docs.google.com/document/d/1TMeLy0TqvAdlYo0IY3Qm4BrzE8i035z9MzYvGl_CzeM/edit by Lou Yang).

Refactor only — no behavior change. Replaces 22 in-source `#ifdef WITH_NVCODEC` directives with self-documenting `XPRS_HAS_NVDEC` (decoder side) and `XPRS_HAS_NVENC` (encoder side) macros, defined by a new `NvCodecConfig.h` single-source-of-truth header. Build-system flags (`-DWITH_NVCODEC=1` in BUCK and CMake) remain as the upstream input.

Why split the macro: today both halves are gated together (`WITH_NVCODEC` is set or unset for both encoder and decoder). The split prepares for build configurations that ship only one half — most importantly the OSS PyPI wheel will want NVDEC without NVENC, since PyPI users typically want decode acceleration but the encode path requires hardware NVIDIA explicitly doesn't support across all SKUs (e.g., A100 has NVDEC but no NVENC). At the call site, `#ifdef XPRS_HAS_NVDEC` makes the intent clear in a way that `#ifdef WITH_NVCODEC` does not.

Files changed:
  NEW arvr/projects/compression/xprs/NvCodecConfig.h — defines XPRS_HAS_NVDEC + XPRS_HAS_NVENC under WITH_NVCODEC, with explanatory comment.
  arvr/projects/compression/xprs/Codecs.h — removed `#include "nvEncoder.h"` (its only consumers — xprsEncApi.cpp, xprsEncoder.cpp, xprs_gtest_common.h — already include nvEncoder.h directly). Adds an explanatory comment so the next reader doesn't re-add it.
  arvr/projects/compression/xprs/xprsDecApi.cpp — added `#include "NvCodecConfig.h"`, replaced 4× `WITH_NVCODEC` with `XPRS_HAS_NVDEC`.
  arvr/projects/compression/xprs/xprsDecoder.h — added include, swapped the nvDecoder.h gate to XPRS_HAS_NVDEC.
  arvr/projects/compression/xprs/xprsDecoder.cpp — added include, consolidated two redundant adjacent `#ifdef WITH_NVCODEC` blocks (one wrapping `cudaContextProvider.h`, one wrapping `Codecs.h` — Codecs.h was unconditionally needed and didn't actually need a guard), used XPRS_HAS_NVDEC.
  arvr/projects/compression/xprs/xprsEncApi.cpp — added include, replaced 6× `WITH_NVCODEC` with `XPRS_HAS_NVENC`, updated TODO comment to reference the new macro.
  arvr/projects/compression/xprs/xprsEncoder.cpp — added include, replaced 2× `WITH_NVCODEC` with `XPRS_HAS_NVENC`.
  arvr/projects/compression/xprs/test/xprs_gtest_codec.cpp — added include, replaced 1× `WITH_NVCODEC` with `XPRS_HAS_NVENC` (test exercises NV encoders by name).
  arvr/projects/compression/xprs/test/xprs_gtest_common.h — added include, replaced 2× `WITH_NVCODEC` with `XPRS_HAS_NVENC`.
  arvr/projects/compression/xprs/BUCK — added `NvCodecConfig.h` to `SUPPORTED_PLATFORMS_HEADERS` so it's exposed to consumers.

NOT changed (out of scope):
  arvr/projects/compression/xprs/CMakeLists.txt — has the existing `target_compile_options` instead of `target_compile_definitions` bug for ENABLE_NVCODEC; D2 fixes this.
  arvr/projects/compression/xprs/BUCK line 209 (`-DWITH_NVCODEC=1`) and the test BUCK / helpers.bzl equivalents — these are intentionally still WITH_NVCODEC since they pass the upstream flag that NvCodecConfig.h reads.
  arvr/projects/oatmeal/acro_conversion/test/BUCK (`-DWITH_NVCODEC=1`) — out-of-tree consumer, unchanged.

Reviewed By: PiotrBrzyski

Differential Revision: D103253723

Author: YLouWashU

xprs/Codecs.h

@@ -18,9 +18,11 @@
 
 #include <string_view>
 
-#ifdef WITH_NVCODEC
-#include "nvEncoder.h"
-#endif
+// Note: nvEncoder.h is intentionally NOT included here. Earlier versions of
+// this header pulled it in under WITH_NVCODEC, but the only consumers
+// (xprsEncApi.cpp, xprsEncoder.cpp, test/xprs_gtest_common.h) include
+// nvEncoder.h directly. Removing it here lets Codecs.h stay free of the
+// XPRS_HAS_NVENC guard.
 
 namespace xprs {
 

xprs/NvCodecConfig.h

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+// Single source of truth for NVIDIA codec compilation guards.
+//
+// `WITH_NVCODEC` is the build-system flag (Buck preprocessor flag, CMake
+// `option(ENABLE_NVCODEC ...)`). Source files should use the self-documenting
+// macros below instead of `WITH_NVCODEC` so it's clear at the call site
+// whether the gated code requires NVDEC (decode), NVENC (encode), or both.
+//
+// Both macros are defined together when WITH_NVCODEC is set. The split into
+// separate macros prepares for build configurations that ship only one half
+// (e.g., OSS distributions that include NVDEC but omit NVENC due to driver,
+// hardware, or licensing constraints).
+
+#ifdef WITH_NVCODEC
+#define XPRS_HAS_NVDEC
+#define XPRS_HAS_NVENC
+#endif

xprs/xprsDecApi.cpp

@@ -15,6 +15,7 @@
  */
 
 #include "Codecs.h"
+#include "NvCodecConfig.h"
 #include "xprsDecoder.h"
 #include "xprsUtils.h"
 
@@ -34,7 +35,7 @@ namespace xprs {
 static const std::string_view kPreferredDecoderImplementations[] = {
     kH265DecoderName,
     kH264DecoderName,
-#ifdef WITH_NVCODEC
+#ifdef XPRS_HAS_NVDEC
     kNvH264DecoderName,
     kNvH265DecoderName,
     kNvAv1DecoderName,
@@ -68,7 +69,7 @@ bool findDecoderByName(const std::string_view& name, VideoCodec& codec) {
   }
 
   // Add custom decoders
-#ifdef WITH_NVCODEC
+#ifdef XPRS_HAS_NVDEC
   if (name == kNvH265DecoderName) {
     codec = VideoCodec{VideoCodecFormat::H265, name.data(), true};
     return true;
@@ -116,7 +117,7 @@ XprsResult enumDecoders(CodecList& codecs, bool hwCapabilityCheck) {
           continue;
         }
         if (codec.hwAccel && hwCapabilityCheck) {
-#ifdef WITH_NVCODEC
+#ifdef XPRS_HAS_NVDEC
           const NvCodecContext nvcodecContext = NvCodecContextProvider::getNvCodecContext();
           if (deviceHasNoHwDecoder(codec.implementationName, nvcodecContext._device_name)) {
             XR_LOGI(
@@ -168,7 +169,7 @@ enumDecodersByFormat(CodecList& codecs, VideoCodecFormat standard, bool hwCapabi
             continue;
           }
           if (codec.hwAccel && hwCapabilityCheck) {
-#ifdef WITH_NVCODEC
+#ifdef XPRS_HAS_NVDEC
             const NvCodecContext nvcodecContext = NvCodecContextProvider::getNvCodecContext();
             if (deviceHasNoHwDecoder(codec.implementationName, nvcodecContext._device_name)) {
               XR_LOGI(

xprs/xprsDecoder.cpp

@@ -19,11 +19,11 @@
 // See xprsDecoder.h for details.
 
 #include "xprsDecoder.h"
-#ifdef WITH_NVCODEC
-#include "cudaContextProvider.h"
-#endif
-#ifdef WITH_NVCODEC
+
 #include "Codecs.h"
+#include "NvCodecConfig.h"
+#ifdef XPRS_HAS_NVDEC
+#include "cudaContextProvider.h"
 #endif
 #include "xprsUtils.h"
 
@@ -47,7 +47,7 @@ CVideoDecoder::~CVideoDecoder() = default;
 XprsResult CVideoDecoder::init(bool disableHwAcceleration) {
   XprsResult result = XprsResult::OK;
   try {
-#ifdef WITH_NVCODEC
+#ifdef XPRS_HAS_NVDEC
     if (implementationName == kNvH264DecoderName || implementationName == kNvH265DecoderName ||
         implementationName == kNvAv1DecoderName) {
       const NvCodecContext nvcodec_context = NvCodecContextProvider::getNvCodecContext();

xprs/xprsDecoder.h

@@ -22,7 +22,8 @@
 #include <memory>
 
 #include "FFmpegDecode.h"
-#ifdef WITH_NVCODEC
+#include "NvCodecConfig.h"
+#ifdef XPRS_HAS_NVDEC
 #include "nvDecoder.h"
 #endif
 #include "xprs.h"