Function decode_capable_gpu_indices 

pub fn decode_capable_gpu_indices(codec: &str) -> Vec<u32>

GPU indices whose vendor decoder can handle codec in this build (honoring the DISABLE_NVDEC* knobs). These are exactly the candidates create_decoder_on(.., Some(idx)) would dispatch a decoder for — the --decode-with-fastest benchmark times each one and pins the pump to the quickest. Order follows detect_gpus().