I was converting a TV show I’d to DVD format using ffmpeg, but the resulting file had the wrong audio channel. At first I thought it had no audio at all, but then I noticed it had a voice over occasionally explaining what was happening; “so-n-so has just entered the room…”.
It appears that ffmpeg had selected the wrong audio stream. For some reason, it had had selected the second audio stream instead of the first. The fix is simple enough, you can manually set the streams to use with the -map option. The command below works well for UK freeview.