Integrate a native Jetson Multimedia API encoder path and keep the existing encoded access-unit contract for RTMP, RTP, and recording consumers.
This adds conditional Jetson MMAPI detection in CMake, builds the required NVIDIA sample common classes into a dedicated support library, and compiles the new backend only when the platform dependencies are present.
The runtime selector now lets encoder.backend=auto prefer Jetson MM for NVIDIA hardware requests while keeping encoder.backend=ffmpeg as an explicit FFmpeg path. Device selection semantics are updated so nvidia requires the Jetson backend, auto can fall back to FFmpeg software, and software remains FFmpeg-only.
The Jetson backend converts supported raw inputs through swscale, feeds NvVideoEncoder in YUV420M, emits Annex-B access units, and harvests decoder configuration from a warmup keyframe so downstream packetizers keep their existing contract.
This also splits FFmpeg encoder option handling into a shared header, updates runtime config/help text and tester defaults, and refreshes compatibility/caveat documentation to reflect the new selection behavior.
Build-tree runtime RPATH handling is tightened so GCC 15 builds keep the matching libstdc++ visible locally. Verification covered GCC 15 builds, RTP H.264/H.265 tester runs, RTMP H.264 stub publish, local live SRS smoke with cvmmap://zed1, and remote execution on 192.168.2.155 using the deployed bundle lib directory for the GCC 15 runtime.
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