+function get_video_trackid {
+ mkvmerge -i "$1" | sed -n 's/Track ID \([0-9]*\): .*video.*/\1/p'
+}
+
+function get_audio_delay {
+ mkvmerge -F json -i "$1" | \
+ jq -r '.tracks[] | select(.type == "audio") | .properties.minimum_timestamp'
+}
+
+function encode_audio {
+ ffmpeg \
+ -i "$1" \
+ -vn \
+ $SLOWFILTER \
+ -c:a libfdk_aac -vbr 3 \
+ "$2"
+}