I often want to create motion videos, that is, videos that only show what changed between frames. Such videos are nice to look at, and so-called “frame differencing” is also the start point for many computer vision algorithms. We have made several tools for creating motion videos (and more) at the University of Oslo: the standalone VideoAnalysis app (Win/Mac) and the different versions of the Musical Gestures Toolbox. These are all great tools, but sometimes it would be nice also to create motion videos in the terminal using FFmpeg.

Typical video files, such as MP4 files with H.264 compression, are usually small in size and with high visual quality. Such files are suitable for visual inspection but do not work well for video analysis. In most cases, computer vision software prefers to work with raw data or other compression formats. The Musical Gestures Toolbox for Matlab works best with these file types: Video: use .jpg (Motion.jpg) as the compression format.

Researchers from AIST have released an open database of dance videos, and I got very excited to try out some visualization methods on some of the files. This was also a good chance to test out some new functionality in the Musical Gestures Toolbox for Matlab that we are developing at RITMO. The AIST collection contains a number of videos. I selected one hip-hop dance video based on a very steady rhythmic pattern, and a contemporary dance video that is more fluid in both motion and music.

I have been doing video analysis on QuickTime (.mov) files for several years, but have never really had the need to use the time information of the movie files. For a project, I now had the need for getting the timecode in seconds out of the files, and this turned out to be a little more tricky than first expected. Hence this little summary for other people that may be in the same situation.

I am happy to announce that a paper I wrote together with Victoria Johnson has just been published in Computer Music Journal. The paper is based on the experiences that Victoria and I gained while working on the piece Transformation for electric violin and live electronics (see video of the piece below). Citation A. R. Jensenius and V. Johnson. Performing the electric violin in a sonic space. Computer Music Journal, 36(4):28–39, 2012.

I spend a lot of time walking around the city with my daughter these days, and have been wondering how much I move and how the movement is distributed over time. To answer these questions, and to try out a method for easy and cheap motion capture, I decided to record today’s walk to the playground. I could probably have recorded the accelerometer data in my phone, but I wanted to try an even more low-tech solution: an audio recorder.

I am teaching a course in sound theory this semester, and therefore thought it was time to update a little program I developed several years ago, called SoundAnalysis. While there are many excellent sound analysis programs out there (SonicVisualiser, Praat, etc.), they all work on pre-recorded sound material. That is certainly the best approach to sound analysis, but it is not ideal in a pedagogical setting where you want to explain things in realtime.

I am teaching two courses this semester: Sound theory 1 (in English) Sound analysis (in Norwegian, together with Rolf Inge Godøy) In both courses I use Pure Data (PD) for demonstrating various interesting phenomena (additive synthesis, beating, critical bands, etc.), and the students also get various assignments to explore such things themselves. There are several PD introduction videos on YouTube in English, but I found that it could be useful to also have something in Norwegian.

To allow everyone to watch their own synchronised spectrograms and motiongrams, I have made a small application called AudioVideoAnalysis. Download AudioVideoAnalysis for OS X (8MB) It currently has the following features: Draws a spectrogram from any connected microphone Draws a motiongram/videogram from any connected camera Press the escape button to toggle fullscreen mode Built with Max/MSP by Cycling ‘74 on OS X.5. I will probably make a Windows version at some point, but haven’t gotten that far yet.