FFmpeg

Hello ,Im trying to remove unwanted clips from a video.
On searching , i got hint to split and concate the video to get final outcome.
i used this code for spliting

"mFfmpegInstallPath "-y" "-i" videoPath "-t" cutstartTime "-c" "copy" split1.mp4 "-ss" cutEndTime "-codec" "copy" split2.mp4"

this code for concating

"mFfmpegInstallPath "-y" "-f" "concat" "-safe" "0" "-i" /join.txt "-c" "copy" output.mp4"

Initially it worked well with mp4 and some of the 3gp videos , but now none of the videos are able to get rendered .

Please point my mistakes, and correct wherever it is .

Thanks in advance