I (obviously) don’t know much about transferring a video signal. What’s different about it than all of the other peripherals that can connect with USB? Does it have anything to do with color (I remember some old CRT monitors that had composite-style cables rather than a VGA cable, with one for each primary color)?
USB doesn’t have nearly enough bandwidth.
USB 2.0 at top speed can transfer somewhere around 480Mb/s. In practice, you’re lucky to get half that.
HDMI/DVI, which is used to send video signals to most HD displays, has a bandwidth of 10+Gb/s, or about 25 times the max bandwidth of USB.
Even a small display would outstrip USB’s capacity.
1024x768 pixels x 32 bits color x 60 Hertz refresh = about 1.5 Gb of video data per second. Realistically, a USB bus could support 640x480 with 16-bit color/greyscale at 30 Hz, or, basically, black and white SD Television.
Might happen with USB 3.0 though, which is supposed to be 10x faster. But current USB also uses quite a bit of your computer’s CPU capacity for transfers. If USB 3.0 doesn’t handle more of the processing load using onboard chips, it still probably won’t be worth sacrificing part of your CPU capacity.
What Walrus said.
Even when highly compressed, video signals are enormous in realtime and also require a significant amount of overhead. The USB standard was designed for data transfer in a non-realtime environment, albeit updated a bit to challenge the new IEEE 1394 (“FireWire”) standard the film industry adopted to deal with the digitalization of editing. (IIRC, USB had a 12-480Mb/s bitrate, while FireWire had 480-4200Mb/s, or 60/600 MB/s respectively.)
However, on Sept. 17th Paul Gelsinger of Intel fame announced USB 3.0 which should reportedly have a 5gb/s bitrate, or 625MB/s - or, in other words, the same bitrate as a PCI-Express graphics card. While this won’t touch the HDMI bitrate spec of about twice as much, it should be interesting to see if USB 3.0 won’t become the lowest common denominator of low-end monitors, like VGA is today, seeing as USB will be ubiquituous with computers for some time yet anyway.
Great info everyone, thanks.
I’ve just evaluated two USB to VGA adapters at work. Obviously, my work there is © them, but I can say that one worked reasonably well for business use, the other fell just short. I wouldn’t use one for home or gaming use.
Did you Google that answer?
[Moderator note]
For the record, this is one of a series of similar inappropriate posts by leander, who was given a caution for another one here.
Since the post was made before I posted my original caution, I am not issuing a warning here, but will for future remarks of this kind.
Colibri
General Questions Moderator
ETA: I note also that SkipMagic issued a warning for a similar post in MPSIMS here.