In this post I will explain how I made some timelapse videos using the Raspberry Pi camera module. This is a two step process which involves getting the camera module to take a series of stills over a period of time and then combining them into an MP4 video file.
We can use the “raspistill” utility to take a set of time lapsed photos as described in my Taking Hi-Res Photos With The Pi Camera Module article. Make sure you have installed the camera and updated your operating system.
Step 1 – Taking the time-lapsed photos
This command will take a photo every 60 seconds (60000 milliseconds) for 2 hours (7200000 milliseconds) resulting in a sequence of 120 images.
raspistill -o myimage_%04d.jpg -tl 60000 -t 7200000
The “%04d” will result in a four digit number appearing in each filename.
myimage_0001.jpg myimage_0002.jpg ... myimage_0119.jpg myimage_0120.jpg
Step 2 – Combine images into MP4 video
Once you’ve got your image sequence you will need a method to stitch them together. I decided to use “avconv”. You can install this useful library with the following command :
sudo apt-get -y install libav-tools
To construct the video file from your image sequence you use the command shown below. Although it appears on multiple lines for readability it should be entered as a single line on the command line :
avconv -r 10 -i myimage_%04d.jpg -r 10 -vcodec libx264 -crf 20 -g 15 timelapse.mp4
The video will be the full resolution of the default image size (2592×1944).
To crop the images and create a more standard 1280×720 resolution video you can use the following command :
avconv -r 10 -i timelapse_%04d.jpg -r 10 -vcodec libx264 -crf 20 -g 15 -vf crop=2592:1458,scale=1280:720 timelapse.mp4
The “vf” option defines a video filter. In this case two filters which crop the incoming image to 2592×1458 and then scale them to 1280×720.
The “r” option tells avconv to create a video with a frames per second of 10. It appears twice to prevent avconv dropping frames that it thinks are similar.
The “crf” option tells avconv to aim for a quality level of “20″ which is a good starting point. Lowers values are better but will increase the file size.
The “-g” option sets the GOP value. The YouTube Advanced Encoding Settings page recommends that the GOP should be set to half the frame rate so this is set to 15.
The conversion process is very slow on the Pi compared to doing the same thing on a desktop PC. For long sequences with hundreds of frames I would recommend downloading an appropriate version of Libav on your desktop or laptop and build your MP4 files much faster!
Here is a quick-n-dirty timelapse video I took out the window of my man-cave. It consists of 600 frames which were taken at a rate of 1 per minute for 10 hours. Nothing much happened in those 10 hours but it proved the Pi could do the job and that avconv could create the MP4. I got a PC to do the hard work!
When I’ve got the time I am going to make some more interesting timelapse videos. But that is for another day. Hopefully with better weather …