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.
Webcams have come along way in the past decade. They’ve gone from a geek-inspiring novelty, producing puny pictures to, in some cases, inexpensive sources of real HD video. Moreover, as their capabilities have improved they have gained acceptance as serious business tools, taking on a significant role in unified communications suites from all the major UC vendors.
All of this implies that a better understanding of webcams can help us to more optimally leverage their capabilities. It can help us to discern the bad from the good, or even great products offered. This can improve how we use video in our daily lives.
So I have set about an exploration of webcams and their ilk, from past experience to present day, and across a variety of use-cases. As always, I approach this with the reckless abandon of an enthusiastic early-adapter.
Modern HDTVs are essentially small embedded computer systems. I was reminded of this fact when I recently purchased a TV for our bedroom. It’s a 32″ Samsung LCD-TV, and it makes little boot-up chimes just like a computer. TV’s are computers…that’s worth remembering.
Recently several large consumer electronics companies have launched new LCD HDTVs in partnership with Skype. This partnership leverages the fact that TVs are computers.
These new model LCD-TVs run an embedded version of the Skype client. When equipped with suitable media handling support (camera, microphone & possibly speakers) these TVs are purported to allow large screen point-to-point video calling via the Skype network.
Not long ago In-Store Solutions launched the Freetalk Everyman HD Webcam for Skype. I’ve had a number of webcams before, even one capable of real “HD.” I bought the Logitech Webcam Pro 9000 last summer when I was trying the LifeSize Desktop video conference client. HD in this application means 1280 x 720 pixels.
So initially I thought that the Freetalk Everyman HD Webcam for Skype was less than exciting. Upon further investigation I find it very interesting for one specific reason; hardware acceleration of H.264 encoding.