Stream #0

Almost a year ago, I invested in a central London based post-production company. At the time, I had dreams of pushing open source software solutions into the professional post-production arena. Things haven’t quite worked out as planned, and I’ve made very limited headway on this project. Business imperatives took over and changing a whole ecosystem is a big job. I’ve continued to use Linux on my laptop and happily connect to printers and network drives, but that’s about all.

Recently I had an opportunity to change all that. We needed a tape digitisation solution, separate from our Avid editing suites, for a new project. I’ve know for a while that Blackmagic’s Decklink range of cards work with Linux and were pretty good for capturing from SDI. We purchased the basic Decklink SDI card, re-cycled an old machine onto which I installed Linux Mint Debian and away we went….

Things weren’t entirely smooth from the start. I upgraded the Mint Debian ISO, including the kernel to 2.6.39. This was my first mistake. The card was not recognised with this kernel. Booting into the original 2.6.32 kernel overcame this problem and the card was recognised. I had to download the relevant Linux software from the Blackmagic website, as the accompanying DVD only included Windows software. The available Linux software from Blackmagic included the relevant drivers, firmware and Media Express software. Unfortunately, other advertised items such as the drive speed test and alpha keying utilities are not available for Linux.

Once everything was up and running, it was time to capture. The Media Express 2.3.1 software was pretty straight forward to use. Setting in and out points allowed the software to control the J30 Digibeta deck and content was captured in Uncompressed 10-bit YUV formate. The other limited codec options included Uncompressed 8-bit YUV, RGB and MotionJPEG. This uncompressed file was then transcoded to IMX50 using FFMbc. The whole process seemed to work reasonably well, and I’m just now waiting to send the IMX50 sample off for technical inspection.

Unfortunately, the Media Express software as supplied did not provide options to change the SD captured frame size from 720×576 to anything else. Ideally I was looking for 720×608 so that VITC was also captured. A phone call to Blackmagic revealed that this was possible with the Windows and Mac version of their software, but not on Linux. Their Linux SDK did expose the necessary calls, but the software had not been written to include them. Essentially, if I wanted VITC, I’d need to write a capture utility myself. Somewhat disappointing.

Overall, I’m pleased that we now have an SDI capture solution running on Linux. However, the Blackmagic Decklink card still feels a little half baked and Linux was perhaps only an afterthought for them.