Open Screen Library supports cross compilation for both arm32 and arm64 platforms, by using the gn args parameter target_cpu="arm" or target_cpu="arm64" respectively. Note that quotes are required around the target arch value.
Setting an arm/arm64 target_cpu causes GN to download a sysroot image from Open Screen's public cloud storage bucket. This image is referenced by GN when building using the compiler --sysroot flag. This allows the compiler to effectively cross compile for different architectures.
Unfortunately, only Google employees can update the sysroots to a new version, by requesting access to the Open Screen pantheon project and uploading a new tar.xz to the openscreen-sysroots bucket.
This documentation is available internally at go/openscreen-cross-compilation-doc.
To run executables on an embedded device, after copying the relevant binaries you may need to install additional dependencies, such as libavcodec and libsdl. For a list of these packages specifically for cast streaming, see the external libraries documentation.