Converting audio tracks only in mkv files to AC3

Question

I have an LG CX TV. The internal video player does not recognise DTS audio format. I'd like to be able to play MKV files (which might have DTS audio tracks) from an external USB device. I was looking into an ffmpeg command that will:

• Leave any and all existing video tracks untouched
• Leave any and all existing subtitles tracks untouched
• Leave any and all existing audio tracks untouched, but crucially - also convert them all to AC3 audio format (at its best quality) and mux them back into the mkv

What ffmpeg command would I need here? So far I think I have it mostly right with this one, but I think this just converts the audio tracks to AC3, not retains the original ones and create AC3 copies.

ffmpeg -i input.mkv -map 0 -vcodec copy -scodec copy -acodec ac3 -b:a 640k output.mkv

Answer 1

bash script:

#!/bin/bash
f="input.mkv"
COD=($(ffprobe -v 0 -select_streams a -show_entries stream=codec_name -of default=nw=1:nk=1 "$f"))
echo ${!COD[@]} → ${COD[@]} → ${#COD[@]}
MAP=()
ENC=()
AU1=${#COD[@]}
for i in "${!COD[@]}"; do
  if [ "${COD[$i]}" != "ac3" ]; then
    MAP+=("-map" "0:a:${i}")
    ENC+=("-c:a:$AU1" "ac3")
    ((AU1++))
  fi
done
ffmpeg -i "$f" -map 0 "${MAP[@]}" -c copy "${ENC[@]}" /tmp/output.mkv -y
ffplay /tmp/output.mkv