[FFmpeg-user] can't concatenate the flv file

[Bqsj Sjbq]

There is a file named input.txt
file '/home/1.flv'
file '/home/2.flv'
I can use the command to Concatenate 1.flv and 2.flv into a mp4 file.
ffmpeg -f concat -i input.txt -c copy output.mp4 #there are two files in output.mp4 
When i use the following command
ffmpeg -i "concat:1.flv|2.flv" -c copy output.mp4  #can run ,but wrong result ,only one file 1.flv in the output.mp4 

why?