Carbon responsible travel

After the pandemic situation became better again, I started looking into travelling from the UK to Germany. Preferably by train, as flying is just not good in a climate crisis. And I travelled by train before several times a year. With the German DB “Super Sparpreis EU” one could book a ticket from London St Pancras to, lets say Dresden or return. Depending on how busy the trains were, I spent something between 70€ and 120€ per direction, maybe a bit more during Christmas. That was 2018.

When I checked this year to travel a month in advance, no public holidays, Prices ware around £75 for the leg London to Brussels and then another £60 to £80 from Brussels to Dresden. I don’t know if that is expensive, it’s definitely over 50% more expensive than 4 years ago.

And then I made the mistake and checked flights. It was shocking to see that they started at £7 for each way. And that was only 2.5 weeks in advance. Luggage adds another £21, and I would need another 17€ for the local train to my final destination. But that is still cheaper than any of the two parts of the train trip for the whole distance.

I understand that these plane ticket prices are not the real costs, the airline will make the money with the people who by tickets at a later stage (although, even for the flight tomorrow the price is still only £18, so probably they need to subsidise from other flights). And yet, I find it astonishing that the climate damaging travel is still cheaper than the more responsible travel.

Experiment: Melting a dyed ice cube in salt water and fresh water – which one melts first?

In a podcast I listened to yesterday the experiment was discussed, using normal ice cubes. And they suggested to repeat the experiment with dyed ice cubes or dyed water. Yesterday I prepared the ice cubes and today did the experiment.

Some words about the preparation: Dissolving salt creates heat, hence I allowed for time so that the water could reach room temperature again. Therefore, the interesting bit only starts after a minute into the time lapse, or 20 minutes in real time.

The ice cubes start melting immediately, both distribute a bit of blue water to their glasses. However, the difference becomes visible very quickly: In the fresh water a constant stream of blue water flows to the bottom of the glass. In the salt water glass the blue melt water from the ice cube creates a layer on the top of the glass. The ice cube swims in this cold water, is isolated from the warm water, and hence survives about twice as long.

The reason of the different behaviour is related to density. A cold liquid has a higher density than a warm liquid, and hence sinks to the bottom (in the same way that a piece of metal has a higher density than water, or humans have a higher density than air). However, dissolving salt in water increases the density of that water, and the saltwater has a higher density than the cold water from the ice cube.

When the experiment was described, I guessed wrong. Using salt to melt ice on streets, I thought the ice cube in the salt water will melt quicker, due to a chemical reactions. However, as the salt is already dissolved, no heat can come from destroying the crystal structure (and that would be a physical reaction and not a chemical reaction anyway).

I didn’t want to show an hour long video on youtube, hence speed up certain parts of the video. For this I used the free ffmpeg tool on a Ubuntu 20 laptop. Running the code below took about 10 Minutes on my Laptop:

ffmpeg -i ../orig.mp4 -ss 00:00:00 -to 00:00:05 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.10*PTS" output_01.mp4 && rm temp.mp4
ffmpeg -i ../orig.mp4 -ss 00:00:05 -to 00:00:27 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.50*PTS" output_02.mp4 && rm temp.mp4
ffmpeg -i ../orig.mp4 -ss 00:00:27 -to 00:00:54 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.10*PTS" output_03.mp4 && rm temp.mp4
ffmpeg -i ../orig.mp4 -ss 00:00:54 -to 00:01:12 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.50*PTS" output_04.mp4 && rm temp.mp4
ffmpeg -i ../orig.mp4 -ss 00:01:12 -to 00:03:05 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.10*PTS" output_05.mp4 && rm temp.mp4
ffmpeg -i ../orig.mp4 -ss 00:03:05 -to 00:03:12 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.33*PTS" output_06.mp4 && rm temp.mp4
ffmpeg -i ../orig.mp4 -ss 00:03:12 -to 00:03:20 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.10*PTS" output_07.mp4 && rm temp.mp4
ffmpeg -i ../orig.mp4 -ss 00:03:20 -to 00:19:50 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.01*PTS" output_08.mp4 && rm temp.mp4
ffmpeg -i ../orig.mp4 -ss 00:19:50 -to 00:20:10 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.10*PTS" output_09.mp4 && rm temp.mp4
ffmpeg -i ../orig.mp4 -ss 00:20:10 -to 00:20:40 -c copy output_80.mp4
ffmpeg -i ../orig.mp4 -ss 00:20:40 -to 00:21:00 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.15*PTS" output_81.mp4 && rm temp.mp4
ffmpeg -i ../orig.mp4 -ss 00:21:00 -to 00:27:11 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.05*PTS" output_82.mp4 && rm temp.mp4
ffmpeg -i ../orig_02.mp4 -ss 00:00:00 -to 00:07:20 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.05*PTS" output_83.mp4 && rm temp.mp4
ffmpeg -i ../orig_02.mp4 -ss 00:07:20 -to 00:07:27 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.15*PTS" output_84.mp4 && rm temp.mp4
ffmpeg -i ../orig_02.mp4 -ss 00:07:27 -to 00:07:42 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.50*PTS" output_85.mp4 && rm temp.mp4
ffmpeg -i ../orig_02.mp4 -ss 00:07:42 -to 00:07:50 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.15*PTS" output_86.mp4 && rm temp.mp4
ffmpeg -i ../orig_02.mp4 -ss 00:07:50 -to 00:27:11 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.05*PTS" output_87.mp4 && rm temp.mp4
ffmpeg -i ../orig_03.mp4 -ss 00:00:00 -to 00:05:11 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.05*PTS" output_88.mp4 && rm temp.mp4
ffmpeg -i ../orig_03.mp4 -ss 00:05:11 -to 00:05:33 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.20*PTS" output_89.mp4 && rm temp.mp4

for f in $(ls output*.mp4); do
ffmpeg -i $f -c copy -bsf:v h264_mp4toannexb -f mpegts $f.ts
CONCAT=$(echo $(ls *.ts) | sed -e "s/ /|/g")
ffmpeg -i "concat:$CONCAT" -c copy -bsf:a aac_adtstoasc VID_20220224_094623206.mp4
rm *.ts

Don’t look up (my personal thoughts)

(by Ronny Errmann)

I finally watched the movie “Don’t look up”. First thought I had at the beginning was how nice that the research environment was shown quite realistic. Not in everything (calculations on a white board instead of using computer programs and knowing it will hit earth with just few hours of position data), but hey, it’s a movie. And second thought was, why is everyone reacting so crazy to the threat.

I really could connect with the feelings of the main characters to get the public and politics react to the threat. In that sense it was quite a stressful movie for me, getting too much involved.

In terms of the climate crisis I feel the same situation as shown in the movie is happening in our real lifes and I wonder if scientists from that field feel like that for years or decades. The impact of humans on the climate is know for over 70 years, and we see the rising temperatures clearly for 40 years. And yet, only slow action is being taken and the things decided are not enough for a 1.5 C limit. If we, the world, keep creating the same amount of CO2, that we created in each of the previous years, then in 8 years will have used up all the budget to keep within the global average of 1.5 C temperature increase. If we use produce more, than we will raise the temperature more than 1.5 C, which will create much more severe effects. And I can’t see any chance that the global emissions will decrease, on the contrary, every year we produce more CO2 than the year before.


Commands to create (time lapse) videos from individual frames

12 Feb 2022 – Ronny Errmann

Some of the time lapses can be found on youtube: Youtube Channel Ronny Errmann, for example an 8 hour time lapse of the night sky over La Palma. If you modify your images before creating a video, creating a working directory and copying the images into that will safe you from accidentally destroying the originals.

Create a Video from images:

mencoder mf://*.jpg -mf fps=24:type=jpg -noskip -vf scale=1156:868 -of lavf -lavfopts format=mp4 -ovc x264 -sws 9 -x264encopts nocabac:level_idc=30:bframes=0:bitrate=16384:threads=auto:turbo=1:global_header:threads=auto:subq=5:frameref=6:partitions=all:trellis=1:chroma_me:me=umh -o output.mp4

The following settings should be adapted to your images:

  • fps=24 : if the framerate of the pictures is not high enough a lower number might be better
  • scale=1156:868 : The pictures of my camera are 3 times bigger along each dimension than the values here, be sure to downsize your images without stretching one axis
  • bitrate=16384 : That bitrate gives reasonable results for my time lapses, however, you might consider larger values (better quality) or smaller values (less storage space needed)

Modify images before creating a video from them:

mogrify -resize 1156x868 IMG_20220212*.jpg

Rotate the images:

mogrify -rotate 90 -background black *.jpg

Crop the images:

To remove useless bits from the image, the values are the new size + start positions

mogrify -crop 3515x2541+142+199 *.jpg

Add exif information to the image, e.g. the time:

Sometimes it’s nice to see the real time running in the time lapse, for this the exif information can be used. In the example the modified images will be copied into “prefix_<original name>”

for img in *jpg; do convert "$img" -gravity SouthEast -pointsize 70 -fill white -annotate +30+30  %[exif:DateTimeOriginal] "prefix_""$img"; done

The following options can be changed:

  • gravity : this gives the corner in which the text should appear. Use geography, e.g. Northwest, South
  • pointsize : size of the text, probably worth to test on a subset of images first (copy images into a subfolder)
  • fill : text colour
  • annotate : distance from the chosen corner

Increase the brightness of the images:

For example, when taking night images and the video is too dark.

mogrify -modulate 200 *.jpg

Video modification for time lapse videos

6 Feb 2022 – Ronny Errmann – last modified on 31 March 2022

Some useful bits which helped me to make the time lapse videos I recorded ready to be published on youtube: Youtube Channel Ronny Errmann

Rotate an mp4 video:

For when the phone was upside down during the recording.

ffmpeg -i input.mp4 -c copy -metadata:s:v rotate="180" output.mp4

Crop an mp4 video:

When personal information is in an area of the video.

1. Get the video resolution:

ffprobe -v error -select_streams v:0 -show_entries stream=width,height -of csv=s=x:p=0 input.mp4

2. Modify the video:

ffmpeg -i input.mp4 -filter:v "crop=1280:600:0:120" output.mp4

Cut an mp4 video:

To keep 00:00:00 to 00:01:22, because afterwards only night was recorded as work had to be finished first.

ffmpeg -i input.mp4 -ss 00:00:00 -to 00:01:22 -c copy output.mp4

Merge/concatenate mp4 videos:

When you notice at the end of a time lapse that the sky is still amazing and you recorded a second one.

Version 1 with the concat protocoll (

Several lines of shell script, run with sh:

for f in $(ls input*.mp4); do
ffmpeg -i $f -c copy -bsf:v h264_mp4toannexb -f mpegts $f.ts
CONCAT=$(echo $(ls *.ts) | sed -e "s/ /|/g")
ffmpeg -i "concat:$CONCAT" -c copy -bsf:a aac_adtstoasc output.mp4
rm *.ts

Use Version 2 if this fails with:

Codec 'mpeg4' (12) is not supported by the bitstream filter 'h264_mp4toannexb'

Version 2 with the concat demuxer (

rm -f mylist.txt; for f in input*.mp4; do echo "file '$f'" >> mylist.txt; done
ffmpeg -f concat -safe 0 -i mylist.txt -c copy output.mp4
rm mylist.txt

Change the speed of mp4 videos:

You took a time lapse, but the viewers are bored, because changes are too small. Time to speed the video up.

ffmpeg -i input.mp4 -r 16 -filter:v "setpts=0.50*PTS" output.mp4

0.5*PTS mean twice the speed, 0.1*PTS would mean ten times the speed, and 2*PTS would mean half the speed.

Change of resolution of mp4 videos:

ffmpeg -y -i input.mp4 -vf scale=480:-2,setsar=1:1 -c:v libx264 -c:a copy output.mp4

The 480 gives the horizontal resultion and the heigh is calculated by keeping the same aspect ratio.

How to code, an additional note

(by Ronny Errmann)

My last post could be read quite negatively, in the way that I didn’t make any progress. So I wanted to add some notes to counteract that feeling. When I looked into new methods actively, because I had a problem, I learned a lot. And I easily remember a few bits from the last years:

  • Replacing loops and conditions with numpy operations on the whole array or part of the array. This made execution so much faster. For example using
array[array > 0] = numpy.average(another_array, axis=1)
  • Making my program compatible to Windows. It’s just a few things to keep Python code compatible to different operating systems.
  • Adding multiprocessing to the program.

All of these helped me to learn new concepts and improve.

How to code, to my younger me

(by Ronny Errmann)

Every time I prepared for interviews or when I started a new role, I learned so many new concepts. Unfortunately, once working in a scientific role, I found it harder to keep this learning up. Making the time to learn about concepts and to talk about code was quite low on my priority list. While reviewing code is something, which I still think is difficult, learning new concepts is something that can easily done. For example, freeing up one hour once or twice a week can make a big difference. Recently I look into C++ methods and just by looking through a few pages of a tutorial (e.g. about classes), I feel I increased my knowledge by a large amount. So there is really no reason to use that as an excuse.

Discussion about code is a bit more difficult. Being the sole programmer in a team doesn’t make things easier, discussion of code means I take time from a different project. Furthermore, in a scientific environment, most people were also self-taught and, like me, only learned the necessary information and were goal driven. But of course, it is important to discuss code and the few experiences, that I have had in the last months, together with the explanation how companies practise these discussions, have changed my view a lot. It is worth the effort, and try to find a group to discuss things can be really beneficial. So similarly to my last post, I would answer to the question, if I would do things differently now with a clear yes.

A beginners code

(by Ronny Errmann)

As mentioned in my last post, I started coding without asking for advice. Which meant I would do things inefficiently. For example to calculate the standard deviation I used the following code:

mittel=sum(l for l in temp)/len(temp)
stdev=math.sqrt(sum((l-mittel)**2 for l in temp)/(len(temp)-1))

Later I learned about numpy, which made things a bit easier:

stdev = numpy.std(temp, ddof=1)

This is also quite a bit more efficient in computing time as it is run in compiled code and not has the overhead of an interpreter language.

Looking back I can smile about the code. In an interview I was once asked about that program if I would do things differently now. To which my answer was a clear yes.

How I came to writing code

(by Ronny Errmann)

The first device I wrote my first programs was the CASIO CFX-9850G, a graphical calculator. We needed it for school (I think 8th grade) and to get it for a lower price, were suggested to buy it even half a year earlier. That was in the mid 90s and, out of interest and out of boredom, I read the manual to see what one can do with it. And by talking to friends, being showed programs from others, I started to understand other people’s code and then tried to solve smaller questions. With time the programs got bigger. In the end I programmed a battleship game and 4 wins, ready to be played in boring lessons against the person sitting next to you. While the programs are long gone (maybe the hand-copied code is still in a folder at my parents place), the calculator is still a part of my desk, although, primarily just as a calculator.

A few years later (or at the same time?) we learned Delphi in School. It was only one year with one or two hours a week, so it couldn’t go into details, however, I know I tried to improve the programs and write more complex ones after school or at home. The GUI made some parts easy, however, looking back it also prevented me from understanding that there is a big benefit for writing back-end code.

After School my interest in coding decreased, mostly because I thought I wasn’t good enough or didn’t see the application. And interest in learning background theory was limited at that age. When I started my Physics studies live was also busy enough. To analyse the laboratory experiments I would work with Excel/OpenOffice Calc and Origin. The built-in functions were enough to solve everything, not elegant, but efficient (in terms of my time).

In my masters project I found the limitations of OpenOffice Calc. To do calculations I just needed so many columns that I would crash it on a regular basis. However, it took until I had to do the first analysis of observational data, that I noticed I need to learn programming. Other people at the institute suggested Python as a start. And so my first basic program was just a python script that would do the steps I would do by hand by itself. It was very procedural, and when I look back, quite funny in how I wrote it. I definitely didn’t search for advice. Luckily this has changed over the years.