sS ffmpeg_argsForMixingVideoAndAudio(File videoIn, File audioIn, File out) {
  ret "-i " + platformQuote(videoIn)
    + " -i " + platformQuote(audioIn)
    + " -c:v copy -c:a aac -strict experimental"
    + " -map 0:v:0 -map 1:a:0"
    + " " + platformQuote(out);
}