printf "file '%s'\n" *.flv > inputs.txt
ffmpeg -f concat -i inputs.txt -c copy output.flv
ffmpeg -f concat -i inputs.txt -c copy output.mp4
printf "file '%s'\n" *.flv > inputs.txt
ffmpeg -f concat -i inputs.txt -c copy output.flv
ffmpeg -f concat -i inputs.txt -c copy output.mp4