Function transcode_codec_args 

pub fn transcode_codec_args(cfg: &Config) -> String

FFmpeg encoder args for the live preview transcode, selected by HELDAR_LIVE_TRANSCODE_ENGINE. software uses libx264 (CPU); vaapi offloads to an Intel/AMD render node; nvenc to an NVIDIA GPU. An unknown engine warns and falls back to software so a typo never breaks live preview.