Note that this requires NO transcoding (conversion), takes just a few seconds, and the resulting filesize will simply be the sum of your input filesizes. In my case, 57 MB total for my 18 minute lecture video.ffmpeg -i input1.mov -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate1.ts ffmpeg -i input2.mov -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate2.ts ffmpeg -i "concat:intermediate1.ts|intermediate2.ts" -c copy -bsf:a aac_adtstoasc output.mp4
By contrast, when I concatenated the same two mov files in iMovie, using exactly the same settings as the input mov files, it took nearly an hour running my CPU so hard it was overheating, and the resulting file was 350 MB. Idiotic iMovie insists on re-encoding the video, which probably degrades the image quality, just to add insult to injury.
I got this method from the ffmpeg docs: