Ffmpeg on Michael’s Domain

Editing Zoom recordings of teaching sessions with FFmpeg

Wed, 25 Nov 2020 00:00:00 +0000

Based on student feedback, we have been organizing a new course for the TRANSMED MSc program about drug discovery and development. It is what you call in German a “Schupperkurs”. I never have found a satisfactory translation of this word in English. It means that we just want to raise the students’ interest in this course. If they like it, they can take any of the many in-depth courses that are offered e.g. at the Faculty of Pharmacy , where there will be more teaching in English in the coming years due to the planned International MSc program in Pharmacy.

ffmpeg

Sun, 26 Jun 2016 00:00:00 +0000

Trimming an avi file: ffmpeg -i Die_Sendung_mit_der_Maus_16.06.19_09-30_ard_30_TVOON_DE.mpg.HQ.avi -vcodec copy -acodec copy -ss 00:06:04 -t 00:29:32 output.aviss is the start time and t is the duration (not the end time)webm to mp3 conversion:ffmpeg -i La_robe_de_soie.webm -vn -ab 128k -ar 44100 -y "La_robe_de_soie.mp3"Concatenate two videos:ffmpeg -f concat -safe 0 -i list.txt -c copy /tmp/output.avilist.txt:file 'video1.avi'file 'video2.avi'UPDATE:It is nice to be able to manipulate video files on the command line. However, especially for the more advanced functionality, the syntax becomes impossible to remember. Hence the need for a GUI that makes ffmpeg more accessible. The best tool that I have come acress so far is the cross-platform LosslessCut . There are also packages for Mac, Linux or Windows .

One firewall to block them all

Tue, 06 Nov 2012 00:00:00 +0000

Helsinki University’s firewall prevents employees from workingWhile I was lying in hospital with a broken calf-bone I couldn’t get any work done because of the Helsinki University’s firewall. Even if the Android OpenVPN client would have allowed me in, I wouldn’t have been able to work. The purpose of a VPN is to allow remote clients the same access to the LAN resources as those machines, that are physically located in the LAN. Obviously Helsinki University doesn’t think so and doesn’t give VPN clients equal privileges. In my case it meant that I cannot ssh into my work computer. This makes remote work expensive, because it required my boss to buy a laptop for me just because the firewall between HY-VPN clients and local machines blocks ssh connections. Without this restriction I could do all the work from my 400€ tablet using e.g. nomachine Player).The work-arounds failed alsoIf I had managed to login into one of the University’s UNIX servers (myntti, kruuna, klaava or ruuvi), I could have logged into my work computer from there. However, my Android ssh client ConnectBot was not able to ssh into them. I presume this to be the fault of my mobile phone network provider Tele Finland , because I couldn’t log into my own ssh servers either (which I normally can, when my Android is connected via WLAN). Once I can connect via ssh to my work computer, I can establish a reverse ssh tunnel and use X Windows or the NoMachine Player to do all the work I usually can when sitting in the laboratory in front of my work computerPlex and no end of video playback troubleHowever, I couldn’t get the OpenVPN configuration right on Android and neither could the helpdesk support to this date. So I was totally bored in the hospital and since we use Plex at home as our media center, I decided to watch some movies. However, Plex is still after four years development in beta and we had our fair share of trouble with media playback. Also this time: I couldn’t play back a single movie or a single song using the Android client . It made the connection to our (Ubuntu 10.04) plexmediaserver without problems, but the only thing that worked was the “Photos” section. By trial and error, I found out that a part of the problem was, that the videos were in Apple’s QuickTime format (they had been encoded on a Mac). So I was looking for a way to batch-convert hundreds of files from .mov into .avi. Certainly this would be faster than filing a bug report and waiting that the Plex guys fix the problem. QuickTime is anyway dead, isn’t it? ffmpeg was certainly the way to go, but Google flooded me with hits concerning batch conversion and the problem was finding the one that works. There is unfortunately lots of crap and noise on the web. The following one-liner did work:find . -name '*.mov' -exec sh -c 'ffmpeg -i "$0" -sameq "${0%%.mov}.avi"' {} \;

youtube to iPod and how to check video files

Mon, 23 Feb 2009 00:00:00 +0000

I was trying to extract the audio file from some youtube videos in order to play it back from my iPod shuffle. I tried various methods (including the otherwise quite versatile VLC Player , but finally settled on the following two step procedure:1. Download the flash video (file ending .flv) file to your local disk. You can use any method to accomplish this task, but as usual Firefox has the perfect plug-in for this task: Download helper .2. Extract and convert the audio file with ffmpeg using the following command: ffmpeg -i video-infile.flv audio-outfile.mp3 It is also possible to convert the flv file into a mpeg file. You need to do this e.g. if you want to import the video into iTunes . For some strange reason Quicktime can play Flash Videos, but iTunes doesn’t allow their playback. The command is almost the same: ffmpeg -i video-infile.flv audio-outfile.mpegAnother nifty usage of ffmpeg is to check video files for corruption and other problems:ffmpeg -v 5 -i file.avi -f null - 2>error.log