Add NVENC (h264_nvenc, hevc_nvenc) encoder support for Linux builds

[willy-scr]

Summary

Add NVIDIA NVENC hardware encoder support (h264_nvenc, hevc_nvenc) to the FFmpeg build for Linux targets.

Changes

New file: compile-nvenc.mjs

• Clones FFmpeg/nv-codec-headers (tag n12.2.16.0) and installs to PREFIX
• Header-only — no library compilation, no runtime dependency at build time
• Only runs on native Linux builds (process.platform === "linux" && !isWindows)

Modified: compile-ffmpeg.mjs

• Import and call enableNvencHeaders(isWindows) alongside other enable* functions
• Add --enable-encoder=h264_nvenc and --enable-encoder=hevc_nvenc to FFmpeg configure
• Guarded by !isWindows && process.platform === "linux" — mirrors the existing VideoToolbox pattern for macOS

Platform impact

Platform	NVENC	Notes
Linux x86_64 glibc	✅ Enabled	Desktop/server with NVIDIA GPUs
Linux x86_64 musl	✅ Enabled	No GPU typically, but harmless
Linux x86_64 musl	✅ Enabled	No GPU typically, but harmless
Linux ARM64 gnu (Lambda)	✅ Enabled	No GPU, harmless
Linux ARM64 musl	✅ Enabled	No GPU, harmless
Windows x86_64	❌ Skipped	Cross-compile complexity
macOS	❌ Skipped	Uses VideoToolbox instead

How it works

1. enableNvencHeaders() clones nv-codec-headers and installs to PREFIX/include/ffnvcodec/ + PREFIX/lib/pkgconfig/ffnvcodec.pc
2. FFmpeg's configure auto-detects NVENC via pkg-config (ffnvcodec package)
3. Since the build uses --disable-encoders + selective re-enable, we explicitly add --enable-encoder=h264_nvenc and --enable-encoder=hevc_nvenc
4. At runtime, NVENC encoders are available if NVIDIA GPU + driver are present; they fail gracefully otherwise

Testing

• CI will build all 7 platform targets — success confirms FFmpeg compiles with NVENC headers
• Runtime NVENC encoding cannot be tested in CI (no GPU on runners)
• Corresponding Remotion PR: @remotion/renderer: Add NVENC hardware encoding for H.264/H.265 on Linux/Windows remotion#7733

[JonnyBurger]

I copied this into #17 so CircleCI can run on a maintainer-owned branch. Once CI passes there, we can review/merge with confidence while preserving your original contribution.

[JonnyBurger]

CircleCI failed on the copied PR: https://app.circleci.com/pipelines/github/remotion-dev/rust-ffmpeg-splitter/436/workflows/5e0302d6-46c8-4783-a298-afcbbab90b1c

Could you take a look and fix the failure? If CircleCI isn’t running for you yet, you may need to sign up for a free CircleCI account first.