mppvideodec outputs NV12 (hardware format) which GStreamer videoconvert
converts to BGRA in scalar software code — slower than avdec_h264 which
uses libav's NEON-optimised YUV→BGRA path.
Default behaviour: software decode (avdec_h264) at PRIMARY rank.
The MPP plugin is still detected and logged so the user knows it is
installed and operational.
Set R36S_HW_DECODE=1 to re-enable the rank boost once a zero-copy
NV12→SDL_UpdateNVTexture (or similar) upload path is implemented.
On linux-aarch64 the conda gst-libav package has an unfixable ABI mismatch
(libdav1d.so.6 missing, libicuuc.so.78 via libxml2-16). Fix: use system
gstreamer1.0-libav installed via apt with GST_PLUGIN_PATH, and preload
system libgomp.so.1 to avoid static TLS block errors when dlopen loads
libgstlibav.so. avdec_h264 and avdec_aac now register correctly on device.
These vars are stored in conda activate.d/gst-env.sh and in deploy/run.sh.
Matteo Benedetto