I have i386 binary that I would like to run on my STB with embedded linux.
How to run i386 binary (compiled on Ubuntu / compiler : i486-linux-gnu-libusb) on MIPS arch platform (set-top box) ?
You need an emulator. The most well-known emulators are qemu and bochs which are both open-source
However emulation is slow by nature, so it's only used for non-performance-critical applications that no source code is available. Real-time software like decoders in a set-top-box definitely isn't suitable to execute under emulation. You need to rebuild the software to MIPS target