How good are USB video cards? | Hacker News Reader

How good are USB video cards?

zdnet.com.au

5 pointsrenai4217 comments

Does anyone remember when ZDNet was a source for the answer to questions like this?

My wife has a Displaylink USB adapter attached to her Macbook so that she can run two external 20" screens.

It's great - it's fast enough for everything that she does (even for videos etc). You only notice you're on a USB adapter when you drag around a window very quickly, or you open Dashboard, and even then - it's not that bad.

(is this really an Ask YC question though?)

Renai: I'm curious given your submission history as to what process you go through in deciding whether or not to submit your articles here - care to comment?

I was coming to complain that the article had basically 0 content. It might not be spam exactly - but if you've only ever submitted from 2 sites - it's not a great look.

The policy here is that there is nothing wrong with submitting your own stuff, as long as it's not spam.

Agreed. Although If you're reading Renai - a large part of the value of HN is commenting. It would be nice if you did so every now and then.

I think that is to make it look like he's not just spamming 'keepingthedoor.com'.

Maybe the title should be "How good are USB video adapters?"

When I saw the title I started thinking about NVIDIA or ATI video cards which is misleading.

I hate that word "adapter" - if you think about it, literally everything is an "adapter".

It's perfectly fine to call it a video card, even though it's not a "card". At least it's more specific than "adapter".

And BTW, ATI and Nvidia are not the only ones with video cards.

I would think that the USB would be a major speed bottleneck and as such it would render the monitor connected to it practically useless, for even watching movies.

EDIT: This is just my totally uninformed guess.

USB 2.0 is 480 Mbit/s (max). I can't find any definite figures for video bandwidth, but I think it would be OK for youtube size, and probably for SD video. Note that since 3D acceleration is done inside the card, it isn't affected by the transfer rate - once it has the textures. Transferring the textures is what takes the bandwidth (assuming the USB card has 3D acceleration).

But for command-line stuff, this delay would be undetectable, similar for reading text (like the Kindle, which has extremely low refresh rate), email, web-browing. Probably, most applications - certainly, most business applications - would be OK on it.

But USB 3.0 will change all that. What's interesting is this may be a disruptive innovation, and the companies who got into while it was still niche are now set up (they know the technical problems, customer technical and business issues; and they have market presence, with end-user customers and retailers etc). That's how you win with a disruptive innovation.

EDIT a review http://www.everythingusb.com/iogear_usb_2.0_external_video_c...

It's nearly impossible to get anywhere near 480 Mbit/s out of USB2. Not only will you normally get maybe half that in ideal situations, you'll churn a ton of CPU pointlessly.

USB's interrupt-driven nature is terrible for pretty much everything but Human Input Devices.

I can't find any definite figures for video bandwidth, but I think it would be OK for youtube size, and probably for SD video

For standard YV12 video, 1080p would be 1920x1080x12 bitsx24fps = 597 mbps.

So you'd probably be good up to 720p at least, but not full HD (unless it's 1920x800, i.e. 1080p with letterboxing black bars cut off).

No, much less than that, after all you could keep a copy of the screen on the other side in a memory buffer and only do the updates on the differences across the cable.

I was talking about video playback, not rendering a static screen.

Yes, well, you are the one that is working on a video codec, so you of all people should know that you can compress video for transmission across a link.

Of course you're not going to transmit that stuff at full framerate uncompressed, that would be pretty silly.

> EDIT: This is just my totally uninformed guess.

you are right, because you are wrong ;) :

http://news.ycombinator.com/item?id=871408

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