#removes first audio stream without transcoding
ffmpeg -i file.mp4 -map 0:0 -map 0:2 -acodec copy -vcodec copy new_file.mp4

#!/bin/bash
for name in *.mkv; do
  ffmpeg -i "$name" -map 0:0 -map 0:2 -acodec copy -vcodec copy "converted/$name"
done