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Howto create time-lapse video in Linux

09.05.2014   ::    téma: Linux
Aurora

Some people in Avast had crazy idea – take all people from R&D (Research and Development), rent a plane and fly 2 200 km (1 400 miles) to north, for amazing teambuilding. This dream becomes true end of March this year. We spend 24 hours at Tromsø, Norway, north of Polar Circle. Our main goal was to see aurora borealis. Full story of this teambuilding is on Avast blog, nice photoreports in albums of Pepa Havlin and Honza Havelka.

I planned to create time lapse video with aurora from series of photos. Two years before, I used Kdenlive video editor for experimenting with time lapse, but result was not smooth. Transitions between photos are disruptive. I don't found any other tool with GUI with better results, so I decided to create video with set of standard command line tools. Some tool for process photo RAWs, ImageMagick for prepare movie frames and avconv for join frames to video.

Step 1: Process RAW photos to JPEGs

I setup my camera to take photo every 20 seconds with 10 seconds explosure and ISO sensitity to 1 600 (aperture F3.5).

First step is convert many RAW photos from camera to jpeg. I tried RawTherapee, RawStudio and UFRaw. I have best experience with UFRaw, that is able minimize noise and support batch processing.

ufraw-batch --conf=aurora_ufraw.xml --out-type=jpeg --compression=100 --exif --out-path=./jpegs *.NEF

Step 2: Resize images to final video resolution

This step is simple. For change resolution of many images is the best tool convert from project ImageMagick.

#!/bin/bash

res=1920x1080
echo "resize to $res..."
mkdir -p resized

i=1
for f in `ls -1 jpegs/*.jpg` ; do
        num=`printf "%0*dn" 4 $i`
        convert $f -resize $res! -quality 100 ./resized/$num.jpg
        i=$(( $i + 1 ))
done
max=$i

Step 3: Create smooth transition between frames

If we want create one minute video with 15 fps (900 frames) from series, that was one hour long originaly and we take photo each 20 seconds (180 photos), we have to use one photo for 5 video frames. In order to smooth result, we have to „morph“ two images to 5 frames transition…

#!/bin/bash

mkdir -p morphed
i=1
while [ $i -lt $(( $max - 1 )) ] ; do
        num=`printf "%0*dn" 4 $i`
        num2=`printf "%0*dn" 4 $(( $i + 1 ))`
        convert resized/$num.jpg resized/$num2.jpg -quality 100 -morph 4 ./morphed/${num}_%05d.jpg
        i=$(( $i + 1 ))
done

Step 4: Create video from frames

We can use avconv utility for joining frames to video. (Avconv is fork of ffmpeg, so we can use ffmpeg too, but arguments can be unlike.)

#!/bin/bash

fps=15
res=1920x1080
bitrate=40000k

echo "rename for avconv..."
i=1
for f in `ls -1 morphed/*.jpg` ; do
        num=`printf "%0*dn" 6 $i`
        mv $f morphed/$num.jpg
        i=$(( $i + 1 ))
done

echo "process with avconv..."
avconv -f image2 -r $fps -s $res -i morphed/%06d.jpg -b:v $bitrate -c:v libx264 -r $fps video.mkv

Result…