You do not need the full bandwidth of USB 2.0 (60 MB/s) to record uncompressed HD video (1080p 60fps). I know it can be confusing to do the conversion from Kb/s to MB/s, but you don't even need to worry about that. Twitch (from what I hear) is not going to let you set your data stream high enough to exceed what USB 2.0 offers (I was told 8,000kbps, or 1MB/s). If you feel like you need something faster they even make these same devices with USB 3.0 capabilities, but you shouldn't need that unless you just want to match USB3 to USB3.
First of all, you're wrong about the bandwidth needed for uncompressed 1080p60:
http://en.wikipedia.org/wiki/Uncompressed_video#Storage_and_Data_Rates_for_Uncompressed_Video (that actually doesn't even show 1080p60 on the chart, but its easy to calculate using the given formula).
Second, I can look up the theoretical top speed of USB 2.0 too.
http://www.everythingusb.com/hi-speed-usb.htmlSince USB 2.0 doesn't get anywhere close to its theoretical bandwidth limit in practice and manufacturers (including Elgato) want their devices to actually "work" in every system they're plugged in to, they don't allow their devices doing live work to come anywhere close to the transfer speed limit. Elgato
does compress the video to fit over USB 2.0, this is a
fact, and they do it with a crappy hardware h.264 encoder (poor quality per bitrate) so that there isn't a huge delay between when the video is input and the video appears on the other side of the capture device (trading off quality for low latency).
Twitch's "cap" (its really a recommended maximum, but if you exceed it and aren't a partner, they'll eventually ban you) is at 3500k bps (lower case k), not 8000. So yeah, this device is fine for Twitch. Its not fine for saving to your hard drive when you want to preserve quality and minimize lossy encoding steps. Which is, you know, what this thread is
actually about.
Furthermore, even for live streaming, Elgato devices have serious problems. There is a delay from the pre-encoding step needed to send the video over USB 2.0, measured in a few hundred milliseconds, and if you don't account for it when you're live streaming, you'll have audio-video sync problems.
For the same price as an Elgato, as long as you have a free PCIe 1x slot, you can get a far better capture card that doesn't pre-encode the video. I previously linked one in this thread. Elgato devices (and all USB 2.0 devices) are a poor choice and should be avoided.
