How to make a time-lapse movie from lots of very boring video?

ffmpeg also has a 'https://trac.ffmpeg.org/wiki/How%20to%20concatenate%20(join,%20merge)%20media%20files' function that should work for joining the files.

Just an update ... thanks everyone for the suggestions. At the moment I am playing around trying to get a scripted solution using ffmpeg working. This is annoyingly complicated by the fact that most Linux distributions seem to ship with ancient versions of it by default. But concatenating the short files, then filtering the output using the setpts option, seems to be the way to go. The only thing that I find a little inelegant about it is that you temporarily need twice as much disk space as the original files consume, or at least I have so far found no way to avoid this. iMovie was a good thought that I really hadn't considered, and it's my #2 solution. However for the record, iMovie is no longer free—Apple now nicks you $15 for it.

iMovie comes bundled with the Mac OS and will do this. There are PC applications that do the same thing.  

Windows Movie Maker is basically the same deal as iMovie, but much more limited in scope. https://www.youtube.com/watch?v=VeWj7JBBKdQ of doing exactly what you asked.

I find the http://shop.gopro.com/softwareandapp/gopro-studio/GoPro-Studio.html#/start=1 app easier to use than iMovie for a lot of purposes, and it has this http://gopro.com/support/articles/how-to-add-slow-motion-or-fast-motion-time-lapse-in-gopro-studio baked in. The GoPro app is free. However, your cheap dashcam .MOV files may or may not be recognized by the app depending on how they're encoded. You may need to convert them first.

Try the search term "hyperlapse," which combines time-lapse with image stabilization.

That is indeed exactly what https://www.youtube.com/watch?v=sA4Za3Hv6ng is intended to do. This is distinct from Instagram's iPhone-only app named hyperlapse which uses the accelerometer data to do the stabilization. Unfortunately neither flavor of hyperlapse will help here since the MSFT version hasn't been commercialized yet as far as I know, and the Instagram version doesn't work on prerecorded material. FFMPEG command line tool is probably the way to go here, as you may be able to batch the job to run on each file, you'll probably have to manually stitch the outputs together in final cut or another editor though.

So just for posterity, here's the solution that seems to work the best, using the output from my particular camera (a G1W-C, sort of a generic $50 Chinese 1080p dashcam that outputs x264 encoded ".mov" files). This is a combination of suggestions given above. ffmpeg seems to have issues with taking large numbers of files as input directly on the commandline, so the trick is to create a text file listing the files you want to merge, and then use that as input. So to make a 20x timelapse from a whole directory of .mov files:for f in *.mov; do echo "file $f" >> files.txt; done[a file called "files.txt" is created]ffmpeg -f concat -i files.txt -an -vcodec libx264 -filter:v 'setpts=0.05*PTS' dashcam.mov[This assumes there are no spaces in the input filenames. If there are, you need more quoting in the for loop. You could also probably shoehorn this into a one-liner if you really wanted to via a subshell, but I don't mind the intermediate file.] This dumps the audio (the -an option), because I couldn't find a good solution to speed up the audio without making it sound like garbage, and it's not that important anyway for what I want (road trip time lapses). In a very pleasant surprise, due to the way this camera writes the files (valid timecode?), ffmpeg is actually smart enough to eliminate the duplicate frames that you'd normally get if you just ran the beginning of one recording into the end of another. At least, I think it is, because I don't notice any jerkiness in the output like I was expecting to see. This is all very camera-dependent, though. The same commands, run against the MKV files produced by a Foscam IP camera, produce very nasty output and a slew of errors, all related to the broken way that the camera writes Matroska output (no valid timestamps). So depending on the type of dashcam you have, you may need to fudge around with some separate commands to preprocess the video. YMMV.