FFmpeg has three concatenation methods:

1. concat video filter

Use this method if your inputs do not have the same parameters (width, height, etc), or are not the same formats/codecs, or if you want to perform any filtering.

Note that this method performs a re-encode of all inputs. If you want to avoid the re-encode, you could re-encode just the inputs that don't match so they share the same codec and other parameters, then use the concat demuxer to avoid re-encoding everything.

ffmpeg -i opening.mkv -i episode.mkv -i ending.mkv \
-filter_complex "[0:v] [0:a] [1:v] [1:a] [2:v] [2:a] \
concat=n=3:v=1:a=1 [v] [a]" \
-map "[v]" -map "[a]" output.mkv

2. concat demuxer

Use this method when you want to avoid a re-encode and your format does not support file-level concatenation (most files used by general users do not support file-level concatenation).

$ cat mylist.txt
file '/path/to/file1'
file '/path/to/file2'
file '/path/to/file3'
    
$ ffmpeg -f concat -safe 0 -i mylist.txt -c copy output.mp4

For Windows:

(echo file 'first file.mp4' & echo file 'second file.mp4' )>list.txt
ffmpeg -safe 0 -f concat -i list.txt -c copy output.mp4

3. concat protocol

Use this method with formats that support file-level concatenation (MPEG-1, MPEG-2 PS, DV). Do not use with MP4.

ffmpeg -i "concat:input1|input2" -codec copy output.mkv

This method does not work for many formats, including MP4, due to the nature of these formats and the simplistic concatenation performed by this method.

If in doubt about which method to use, try the concat demuxer.

Also see

• FFmpeg FAQ: How can I join video files?
• FFmpeg Wiki: How to concatenate (join, merge) media files

Try using this. It is the fastest and best ffmpeg-way I have figure it out:

 ffmpeg -ss 00:01:00 -i input.mp4 -to 00:02:00 -c copy output.mp4

This command trims your video in seconds!

Explanation of the command:

-i: This specifies the input file. In that case, it is (input.mp4).
-ss: Used with -i, this seeks in the input file (input.mp4) to position.
00:01:00: This is the time your trimmed video will start with.
-to: This specifies duration from start (00:01:40) to end (00:02:12).
00:02:00: This is the time your trimmed video will end with.
-c copy: This is an option to trim via stream copy. (NB: Very fast)

The timing format is: hh:mm:ss

Please note that the current highly upvoted answer is outdated and the trim would be extremely slow. For more information, look at this official ffmpeg article.