FFmpeg split video and merge back

Using trim and concat – source files with different codecs

For this, make sure that your individual files have the same resolution, and ideally same framerate and chroma subsampling etc. This will prevent errors or glitches during concatenation.

You can do everything in one go without splitting the file, using the trim and concat filters:

ffmpeg -i edv_g24.mp4 -i short-video.mp4 -filter_complex "\
[0:v]trim=0:10,setpts=PTS-STARTPTS[v0]; \
[1:v]trim=0:5,setpts=PTS-STARTPTS[v1]; \
[0:v]trim=15:30,setpts=PTS-STARTPTS[v2]; \
[v0][v1][v2]concat=n=3:v=1:a=0[out]" \
-map "[out]" output.mp4

Here, trim is used to specify the individual portions of the input video streams (0:v, 1:v) that you later want to concatenate. These parts are named v0 through v2. (The setpts filter resets the timestamps of these individual parts to 0, which is required for concatenation). Later, we concatenate the three parts.

If you want to trim from a certain timestamp to the end, use trim=start=15 instead of specifying the range.

If your files have audio, you have to trim those streams separately:

ffmpeg -i edv_g24_2.mp4 -i short-video.mp4 -filter_complex "\
[0:v]trim=0:10,setpts=PTS-STARTPTS[v0]; \
[0:a]atrim=0:10,asetpts=PTS-STARTPTS[a0]; \
[1:v]trim=0:5,setpts=PTS-STARTPTS[v1]; \
[1:a]atrim=0:5,asetpts=PTS-STARTPTS[a1]; \
[0:v]trim=15:30,setpts=PTS-STARTPTS[v2]; \
[0:a]atrim=15:30,asetpts=PTS-STARTPTS[a2]; \
[v0][a0][v1][a1][v2][a2]concat=n=3:v=1:a=1[outv][outa]" \
-map "[outv]" -map "[outa]" output.mp4

Note that video and audio will be re-encoded in this case – make sure to specify appropriate output quality targets (e.g. -crf for x264, x265 or libvpx-vp9). You can read more about this on the FFmpeg Wiki, e.g. for VP9 or H.264.

Using individual segments

If you want to split the clips and later reassemble them:

ffmpeg -i edv_g24.mp4 -ss 0 -to 10 -c copy part1.mp4
ffmpeg -i edv_g24.mp4 -ss 10 -to 15 -c copy part2.mp4
ffmpeg -i edv_g24.mp4 -ss 15 -c copy part3.mp4

ffmpeg -i part1.mp4 -i short-video.mp4 -i part3.mp4 -filter_complex \
"[0:v][1:v][2:v]concat=n=3:v=1:a=0[outv]" \
-map "[outv]" -t 30 output.mp4

If the files have audio, use the same approach as above:

ffmpeg -i part1.mp4 -i short-video.mp4 -i part3.mp4 -filter_complex \
"[0:v][0:a][1:v][1:a][2:v][2:a]concat=n=3:v=1:a=1[outv][outa]" \
-map "[outv]" -map "[outa]" -t 30 output.mp4

This will again re-encode the video stream. It's a little more straightforward but otherwise should be equivalent to the above method.

Using concat demuxer

You can in principle also try to concatenate the bitstreams without re-encoding them, using the concat demuxer. Create a file called concat.txt and add the following entries (corresponding to the video clips created above):

file 'part1.mp4'
file 'short-video.mp4'
file 'part3.mp4'

Then concatenate these individual files:

ffmpeg -f concat -i concat.txt -c copy output.avi

This however requires your clips to have the same codec, resolution, framerate etc. – so it doesn't work with all kinds of heterogenous sources.

Using concat protocol

The above kind of file-level concatenation can be achieved using the concat protocol as well, with the same kind of constraints as above (same codec, resolution, etc.):

ffmpeg -i "concat:part1.avi|part2.avi|part3.avi" -c copy output.mp4

For more info on concatenation, read the respective FFmpeg Wiki page.