Time lapse videos

Just recently, I needed to create time lapse videos out of a list of short video snippets (roughly 2 minutes each).

The result can be found on GitHub.

It does only process video. Audio is — of course — omitted. Also, it does not mux audio tracks automatically into the final time lapse video. If you want your music, then you need to post process it with your tool of choice.

Basics

What I found on several locations on the internet helped me creating this shell script.

What needs to be done in two steps. Apparently, ffmpeg cannot process the time lapse video directly from normal speed videos. That’s why you need two steps until final result:

1. Create stills (as images) on a regular basis
2. Combine these stills as one time lapse video file

It also helps, if you have more than one input video to process into one time lapse video (aka concatenate them into one).

Details

The script expects one or more folders in the current folder. One folder will be combined into one time lapse video. Every folder must contain at least one video file. Multiple levels of folders are not supported.

For every folder, a temporary folder will be created to receive all the images. If the temporary folder already exists, it will take it and directly generate the final time lapse video.

If the final time lapse video exists, this input folder will be skipped.

Commands

If the script is not needed, but my investigation might be of help, here are the commands explained, and what they do. For details on the arguments, look at the ffmpeg documentation.

Generate stills

With the following command, one input video will be used to generate images on a regular basis:

ffmpeg -i INPUT_VIDEO -r 1 -f image2 -vsync cfr tmpdir/%05d.png

Technically, it will save one frame per second.

Unfortunately, I did not manage to insert an actual timestamp into this image showing the actual timestamp when this scene in the video actually happened [1].

Note

Look at the %05d. It will be replaced by a running number with leading zeros [2]. You can also prefix it with the input video file name, it will mitigate the issue, if you have more than one input video file for one final time lapse video.

Generate final time lapse video

As you might already foresee is, the final frame rate you’re using will determine the speed of your time lapse video:

ffmpeg -pattern_type glob -i 'tmpdir/*.png' -c:v libx265 -crf 26 -pix_fmt yuv420p OUTPUT_VIDEO.Extension

If you don’t give an argument for targeted frame rate, ffmpeg will use 25 fps [3].

Footnotes

[1]	I’m using a webcam generating a 2 minute video on activity. These original video snippets contain a correct date and time information in their metadata, when it was captured. But the frames do not contain this information. That’s why I think it needs to be calculated with ffmpeg somehow.

[2]	Interestingly, I’ve received an error message from ffmpeg if this value is too big. So be careful with this number.

[3]	Look at the ffmpeg documentation for details

[4]	Use the comand ffmpeg -encoders to list all available codecs.