When is a webcam not a webcam? When it’s actually a DSLR!
Around here we are strong believers in DSLRs. Our first DSLR was an Olympus E-10, but these days we have a couple of Canon Rebel XSi’s. Released in Q1-2009 these are not the latest and greatest by any stretch, but they’re nice cameras. We also have a small selection of lenses.
As DSLRs have come to shoot video it would make some sense that they could also be used the more sedate role of webcam. Our Rebel XSi’s don’t shoot video, but they do make nice 12 mega-pixel pictures.
It happens that many Canon cameras, including the XSi, have a feature called “Live View” that’s intended to stream the image to the LCD viewfinder or even across a USB connection.
Have you ever noticed that basically all webcams are connected to the host computer using the USB 2.0 bus? The ubiquitous USB 2.0 bus is cheap and convenient for such purposes. Providing 480 Mbps it’s no slouch, but it’s not exactly state-of-the-art either. This has implications when webcams are reaching for HD resolutions at decent frame rates.
Until quite recently webcams always provided an uncompressed image stream to the host computer. USB 2.0 is a serial connection standard supporting up to 480 Mbps. That’s about one third of the data rate of the production HD-SDI standard, SMPTE-292M, which is 1.485 Gbps.
Let’s do a little math corresponding to a 720p video stream as related to uncompressed HDTV.
8 bit/pixel @ 1280 x 720 @ 59.94fps = 105 MB per/sec, or 370 GB per/hr.
105 MB/s = 840 mbps
…but a lot of video conferencing gear actually uses 30 frames/second instead of 59.94 or 60 frames/second…so half that value…
720p30 = 420 mbps!
There you have it! The mathematics supports the assertion that 720p30 uncompressed “HD” video stream can be passed across the USB 2.0 serial bus. This explains how Skype, Google, ooVoo, VSee and others have been able to offer HD video using common USB 2.0 connected webcams. Understanding the limit of the USB 2.0 connection also informs us why 1080-capable webcams have not become similarly commonplace.
Normally, products announcements for the iPad don’t even register on my radar. However, as I recently purchased a third generation iPad with the Retina display I thought this a fine opportunity to revisit VSee.
We have invited the folks from Twelephone to appear as guests on the VUC call Friday, December 28th. If you’ve not heard of them, Twelephone is a new video calling service built using WebRTC and effectively leveraging Twitter as namespace. It’s just one of many new web communications applications arising from from the newly evolved WebRTC standard.
Chris Mathieu is the founder of the project. Chris has appeared on a number of VUC calls in the past. Chris has long been involved with telecom related APIs, including spending some time worth with the Voxeans who created Tropo.
For quite some time I’ve been looking for a way to leverage things like Skype video calling, Google Hangouts or Citrix GotoMeeting with HD Faces. However, I don’t want to use a webcam as the video source. I want to use a real, high-quality video source….preferably an HD-SDI video source.
Clearly I’ve got my own reasons for this sort of requirement. I work with equipment that outputs production grade video. By “production grade” I mean entirely uncompressed video. That’s 270 Mbps for SD and 1.459 Gbps for HD. It’s very clean video.
There are times when I need to be able to stream this kind of video to a remote site. Of course it’s not practical to send the uncompressed stream wholly unaltered. Well, it could be done, but for a hefty price.
Since the far end is typically an ad hoc location what I really need is a way to use an uncompressed HD-SDI source, but deliver a decent quality, sensibly compressed stream to something handy at the far end. It would be most ideal if it didn’t require an installed app to receive the stream. Finally, it should handle firewalls and NAT without flinching.
There’s a new tool in the office and I’m actually pretty excited about it. For several months I’ve had the Black Magic DesignIntensity Pro video capture card. It’s a little PCIe card that has a variety inputs, most notably HDMI in and out.