[FFmpeg-user] Concatenate aac streams leaves "gap"

[MooYoul Lee]

Hi all.

I'm trying to encode an audio file in parallel.
so current workflow is like below:

1. split input audio using segment muxer
- $ ffmpeg -i long-audio.mka -c copy -f segment -segment_time 5 out-%03d.mka
2. encode each segment
- $ ffmpeg -i out-000.mka -c:a libfdk_aac -b:a 96k -cutoff 16000
out-reencoded-000.mka
3. concat encoded segments
- $ printf "file '%s'\n" ./*.mka > mylist.txt
- $ ffmpeg -f concat -i mylist.txt -c copy merged.mka

but when i play merged audio file, i can hear a little "gap" on every split
point (e.g. every 5s)

below link seems similar issue,
https://stackoverflow.com/questions/46577437/ffmpeg-concat-drops-audio-frames/46577994

how can i safely re-encode segments, and safely concat them without hearing
gaps?