Unix

Here's another entry in my "remind myself without searching the entire internet" series of posts. I often want to convert a non-native video into a QuickTime-compatible format. In one oft-repeated use, I have a time lapse camera that outputs AVI files that QuickTime cannot read. Using Don Melton's Other Video Transcoding tools, converting between the two forms is pretty easy:

other-transcode --hevc --mp4 input_file.m4v

The output file will reside in the same directory, with the same name, but with the mp4 extension. I know there are tons of ways to do this, and many offer much more control over the final quality. For my time lapse camera videos, though, the quality is fine and this is really easy to use.

I had two short video clips I wanted to merge into one, each about 8MB in size. I first did this using QuickTime Player's Clips feature, but the end result was over 100MB in size. For my second try, I switched to ffmpeg, which can be installed via Homebrew, MacPorts, or some other method.

This isn't quite as simple as typing one command, as ffmpeg wants to process a list of files to merge—it can't, without some Unix wizardry, accept a list on the command line. So step one is to create a text file (list.txt in my example) in the same directory as your video files. The file contains a list of each movie to be merged, one entry per row, like this:

file '/full/path/to/movie1.mp4'
file '/full/path/to/movie2.mp4'
file '/full/path/to/movie3.mp4'
etc.

Save the text file, then use this command to merge the movies into one:

ffmpeg -f concat -safe 0 -i list.txt -codec copy merged_movie.mp4

When done, you'll have one new movie with all of the listed movies, in the order in which you listed them. And best of all, the size won't balloon when you do so—using the same movies as I used in QuickTime Player, the finished file was just 28MB in size. This isn't limited to mp4s; you can merge any type of video that ffmpeg can handle.

And yes, this is another entry in my series of "remind myself" posts; I originally found the answer on Stack Overflow.

This post is another in an ongoing series where the sole point of the post is to make it easier for me to find this information in the future—instead of searching sites and finding tons of wrong answers, I can just search my blog and find the right answer. If it's useful to anyone else, that's a bonus.

Sometimes, I want to reverse a video, usually for humorous effect—to turn a disassembly time lapse video into an assembly time lapse video, for example. If you have ffmpeg installed (via Homebrew or MacPorts or other method), then it's quite simple to do. Here's the command:

ffmpeg -i original_movie.mp4 -vf reverse -af areverse new_reverse_movie.mp4

It doesn't have to be an mp4, of course—any format that ffmpeg can deal with will work fine.

(I originally found this solution on StackExchange.)