Nvidia Jetson ffmpeg + TensorRT support (#6458)

* Non-Jetson changes

Required for later commits:
- Allow base image to be overridden (and don't assume its WORKDIR)
- Ensure python3.9
- Map hwaccel decode presets as strings instead of lists
Not required:
- Fix existing documentation
- Simplify hwaccel scale logic

* Prepare for multi-arch tensorrt build

* Add tensorrt images for Jetson boards

* Add Jetson ffmpeg hwaccel

* Update docs

* Add CODEOWNERS

* CI

* Change default model from yolov7-tiny-416 to yolov7-320

In my experience the tiny models perform markedly worse without being
much faster

* fixup! Update docs

docker/tensorrt/build_jetson_ffmpeg.sh

@@ -0,0 +1,59 @@
+#!/bin/bash
+
+# For jetson platforms, build ffmpeg with custom patches. NVIDIA supplies a deb
+# with accelerated decoding, but it doesn't have accelerated scaling or encoding
+
+set -euxo pipefail
+
+INSTALL_PREFIX=/rootfs/usr/local
+
+apt-get -qq update
+apt-get -qq install -y --no-install-recommends build-essential ccache clang cmake pkg-config
+apt-get -qq install -y --no-install-recommends libx264-dev libx265-dev
+
+pushd /tmp
+
+# Install libnvmpi to enable nvmpi decoders (h264_nvmpi, hevc_nvmpi)
+if [ -e /usr/local/cuda-10.2 ]; then
+    # assume Jetpack 4.X
+    wget -q https://developer.nvidia.com/embedded/L4T/r32_Release_v5.0/T186/Jetson_Multimedia_API_R32.5.0_aarch64.tbz2 -O jetson_multimedia_api.tbz2
+else
+    # assume Jetpack 5.X
+    wget -q https://developer.nvidia.com/downloads/embedded/l4t/r35_release_v3.1/release/jetson_multimedia_api_r35.3.1_aarch64.tbz2 -O jetson_multimedia_api.tbz2
+fi
+tar xaf jetson_multimedia_api.tbz2 -C / && rm jetson_multimedia_api.tbz2
+
+wget -q https://github.com/madsciencetist/jetson-ffmpeg/archive/refs/heads/master.zip
+unzip master.zip && rm master.zip && cd jetson-ffmpeg-master
+LD_LIBRARY_PATH=$(pwd)/stubs:$LD_LIBRARY_PATH   # tegra multimedia libs aren't available in image, so use stubs for ffmpeg build
+mkdir build
+cd build
+cmake .. -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=$INSTALL_PREFIX
+make -j$(nproc)
+make install
+cd ../../
+
+# Install nv-codec-headers to enable ffnvcodec filters (scale_cuda)
+wget -q https://github.com/FFmpeg/nv-codec-headers/archive/refs/heads/master.zip
+unzip master.zip && rm master.zip && cd nv-codec-headers-master
+make PREFIX=$INSTALL_PREFIX install
+cd ../ && rm -rf nv-codec-headers-master
+
+# Build ffmpeg with nvmpi patch
+wget -q https://ffmpeg.org/releases/ffmpeg-6.0.tar.xz
+tar xaf ffmpeg-*.tar.xz && rm ffmpeg-*.tar.xz && cd ffmpeg-*
+patch -p1 < ../jetson-ffmpeg-master/ffmpeg_patches/ffmpeg6.0_nvmpi.patch
+export PKG_CONFIG_PATH=$INSTALL_PREFIX/lib/pkgconfig
+# enable Jetson codecs but disable dGPU codecs
+./configure --cc='ccache gcc' --cxx='ccache g++' \
+            --enable-shared --disable-static --prefix=$INSTALL_PREFIX \
+            --enable-gpl --enable-libx264  --enable-libx265 \
+            --enable-nvmpi --enable-ffnvcodec --enable-cuda-llvm \
+            --disable-cuvid --disable-nvenc --disable-nvdec \
+    || { cat ffbuild/config.log && false; }
+make -j$(nproc)
+make install
+cd ../
+
+rm -rf /var/lib/apt/lists/*
+popd