Testing Blackmagic Web Presenter

Blackmagic Web PresenterWe are rapidly moving towards the start of our new Master’s programme Music, Communication & Technology. This is a unique programme in that it is split between two universities (in Oslo and Trondheim), 500 kilometres apart. We are working on setting up a permanent high-quality, low-latency connection that will be used as the basis for our communication. But in addition to this permanent setup we need solutions for quick and easy communication. We have been (and will be) testing a lot of different software and hardware solutions, and in a series of blog posts I will describe some of the pros and cons of these.

Today I have been testing the Blackmagic Web Presenter. This is a small box with two video inputs (one HDMI and one SDI), and two audio inputs (one XLR and one stereo RCA). The box functions as a very basic video/audio mixer, but the most interesting thing is that it shows up as a normal web camera on the computer (even in Ubuntu, without drivers!). This means that it can be used in most communication platforms, including Skype, Teams, Hangouts, Appear.in, Zoom, etc., and be the centerpiece of slightly more advanced communication.

My main interest in testing it now was to see if I could connect a regular camera (Canon XF105) and a document camera (Lumens DC193) to the device. As you can see in the video below, this worked flawlessly, and I was able to do a quick recording using the built-in video recorder (Cheese) in Ubuntu.

So to the verdict:

Positive:

  • No-frills setup, even on Ubuntu!
  • Very positive that it scales the video correctly. My camera was running 1080i and the document camera 780p, and the scaling worked flawlessly (you need the same inputs for video transition effects to work, though, but not really a problem for my usage).
  • Hardware encoding makes it easy to connect also to fairly moderate PCs.
  • Nice price tag (~$500).

Negative:

  • Most people have HDMI devices, but SDI is rare. We have a lot of SDI stuff, so it works fine for our use.
  • No phantom power for the XLR. This is perhaps the biggest problem, I think. You can use a dynamic microphone, but I would have preferred a condenser. Now I ended up connecting a wireless lavalier microphone, with a line-level XLR connection in the receiver. It is also possible to use a mixer, but the whole point of this box is to have a small, portable and easy set up.
  • 720p output is ok for many things we will use it for, but is not particularly future-proof.
  • It has a fan. It makes a little more noise than when my laptop fan kicks in, but is not noticeable if it is moved one meter away.

Not perfect, but for its usage I think it works very nicely. For meetings and teaching where it is necessary to have a little more than just a plain web camera, I think it does it job nicely.

Trim video file using FFMPEG

This is a note to self, and hopefully to others, about how to easily and quickly trim videos without recompression.

Often I end up with long video recordings that I want to split or trim. One a side note sometimes people call this “cropping”, but in my world cropping is to cut out parts of the image, that is, a spatial transformation. Splitting and trimming are temporal transformations.

You can of course both split and trim in most video editing software, but these will typically also recompress the file on export. This reduces the quality of the video, and it also takes a long time. A much better solution is to trim losslessly, and fortunately there is a way to do this with the wonder-tool FFMPEG. Being a command line utility (available on most platforms) it has a ton of different options, and I never remember these. So here it goes, this is what I use (on Ubuntu) to trim out parts of a long video file:

This will cut out the section from about 1h19min to 2h18min losslessly, and will only take a few seconds to run.

From Basic Music Research to Medical Tool

The Research Council of Norway is evaluating the research being done in the humanities these days, and all institutions were given the task to submit cases of how societal impact. Obviously, basic research is per definition not aiming at societal impact in the short run, and my research definitely falls into category.Still it is interesting to see that some of my basic research is, indeed, on the verge of making a societal impact in the sense that policy makers like to think about. So I submitted the impact case “From Music to Medicine”, based on the system Computer-based Infant Movement Assessment (CIMA).

Musical Gestures Toolbox

CIMA is based on the Musical Gestures Toolbox, which started its life in the early 2000s, and which (in different forms) has been shared publicly since 2005.

My original aim of developing the MGT was to study musicians’ and dancers’ motion in a simple and holistic way.The focus was always on trying to capture as much relevant information as possible from a regular video recording, with a particular eye on the temporal development of human motion.

The MGT was first developed as standalone modules in the graphical programming environment Max, and was in 2006 merged into the Jamoma framework. This is a modular system developed and used by a group of international artists, under the lead of Timothy Place and Trond Lossius. The video analysis tools have since been used in a number of music/dance productions worldwide and are also actively used in arts education.

Studying ADHD

In 2006, I presented this research at the annual celebration of Norwegian research in the Oslo concert hall, after which professor Terje Sagvolden asked to test the video analysis system in his research on ADHD/ADD at Oslo University Hospital. This eventually lead to a collaboration in which the Musical Gestures Toolbox was used to analyse 16 rat caves in his lab. The system was also tested in the large-scale clinical ADHD study at Ullevål University Hospital in 2008 (1000+ participants). This collaboration ended abruptly with Sagvolden’s decease in 2011.

Studying Cerebral Palsy

The unlikely collaboration between researchers in music and medicine was featured in a newspaper article and a TV documentary in 2008, after which physiotherapist Lars Adde from the Department of Laboratory Medicine, Women’s and Children’s Health at the Norwegian University of Science and Technology (NTNU) called me to ask whether the tools could also be used to study infants. This has led to a long and fruitful collaboration and the development of the prototype Computer-based Infant Movement Assessment (CIMA) which is currently being tested in hospitals in Norway, USA, India, China and Turkey. A pre-patent has been filed and the aim is to provide a complete video-based solution for screening infants for the risk of developing cerebral palsy (CP).

It is documented that up to 18% of surviving infants who are born extremely preterm develop cerebral palsy (CP), and the total rate of neurological impairments is up to 45%. Specialist examination may be used to detect infants in the risk of developing CP, but this resource is only available at some hospitals. The CIMA aims to offer a standardised and affordable computer-based screening solution so that a much larger group of infants can be screened at an early stage, and the ones that fall in the risk zone may receive further specialist examination. Early intervention is critical to improving the motor capacities of the infants. The success of the CIMA methods developed on the MGT framework are to a large part based on the original focus on studying human motion through a holistic, simple and time-based approach.

The unlikely collaboration was featured in a new TV documentary in 2014.

References

  • Valle, S. C., Støen, R., Sæther, R., Jensenius, A. R., & Adde, L. (2015). Test–retest reliability of computer-based video analysis of general movements in healthy term- born infants. Early Human Development, 91(10), 555–558. http://doi.org/10.1016/j.earlhumdev.2015.07.001
  • Jensenius, A. R. (2014). From experimental music technology to clinical tool. In K. Stens\a eth (Ed.), Music, health, technology, and design. Oslo: Norwegian Academy of Music. Retrieved from http://urn.nb.no/URN:NBN:no-46186
  • Adde, L., Helbostad, J., Jensenius, A. R., Langaas, M., & Støen, R. (2013). Identification of fidgety movements and prediction of CP by the use of computer- based video analysis is more accurate when based on two video recordings. Physiotherapy Theory and Practice, 29(6), 469–475. http://doi.org/10.3109/09593985.2012.757404
  • Jensenius, A. R. (2013). Some video abstraction techniques for displaying body movement in analysis and performance. Leonardo, 46(1), 53–60. http://urn.nb.no/URN:NBN:no-38076
  • Adde, L., Langaas, M., Jensenius, A. R., Helbostad, J. L., & Støen, R. (2011). Computer Based Assessment of General Movements in Young Infants using One or Two Video Recordings. Pediatric Research, 70, 295–295. http://doi.org/10.1038/pr.2011.520
  • Adde, L., Helbostad, J. L., Jensenius, A. R., Taraldsen, G., Grunewaldt, K. H., & Støen, R. (2010). Early prediction of cerebral palsy by computer-based video analysis of general movements: a feasibility study. Developmental Medicine & Child Neurology, 52(8), 773–778. http://doi.org/10.1111/j.1469-8749.2010.03629.x
  • Adde, L., Helbostad, J. L., Jensenius, A. R., Taraldsen, G., & Støen, R. (2009). Using computer-based video analysis in the study of fidgety movements. Early Human Development, 85(9), 541–547. http://doi.org/10.1016/j.earlhumdev.2009.05.003
  • Jensenius, A. R. (2007). Action–Sound: Developing Methods and Tools to Study
    Music-Related Body Movement (PhD thesis). University of Oslo.
    http://urn.nb.no/URN:NBN:no-18922

Simple video editing in Ubuntu

I have been using Ubuntu as my main OS for the past year, but have often relied on my old MacBook for doing various things that I haven’t easily figured out how to do in Linux. One of those things is to trim video files non-destructively. This is quite simple to do in QuickTime, although Apple now forces you to save the file with a QuickTime container (.mov) even though there is still only MPEG-4 compression in the file (h.264).

There are numerous linux video editors available, but most of these offer way too many features and hence the need to re-compress the files. But I have found two solutions that work well.

The first one, ffmpeg, should be obvious, although I hadn’t thought that it could also do trimming. However, I often like GUI software, and I have found that Avidemux can do what I need very easily. Just open a file, add start and stop markers for the section to be trimmed, and click save. As opposed to QuickTime, it also allows for saving directly to MPEG-4 files (.mp4) without recoding the file.

There was only one thing that I had to look up, and that was the need for starting the trim section on a keyframe in the video. This is quite obvious when wanting to avoid re-encoding the file, but unfortunately Avidemux doesn’t help in explaining this but only gives an error message. The trick was to use the >> arrows to jump to the next keyframe, and then the file saved nicely.