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Cheap HDMI capture for Linux

blog.benjojo.co.uk

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Re: Cheap HDMI capture for Linux

#51

Post by riskable »

rsync wrote: post #50

"These units are not perfect for quality, however they are not bad at all, Here is a screenshot taken on my laptop..." I am confused by this ... HDMI is a digital interconnect and deals in digital I/O ... in my mind, if you succeed in capturing that HDMI, the resulting stream should be identical ... why would there be a quality (or any other) difference ?

Because they compress the video before sending it over IP. Nothing fancy, just M-JPEG which is basically the same thing as taking a screenshot of the video every nth of a second and saving it as a high-quality JPEG (probably around 95% quality rating).

The screenshot in the video suggests 1000fps but that figure is highly dubious. It is much more likely to be 30 or 60fps on a cheap HDMI->IP converter like this.

Re: Cheap HDMI capture for Linux

#52

Post by antoinealb »

rsync wrote: post #50

"These units are not perfect for quality, however they are not bad at all, Here is a screenshot taken on my laptop..." I am confused by this ... HDMI is a digital interconnect and deals in digital I/O ... in my mind, if you succeed in capturing that HDMI, the resulting stream should be identical ... why would there be a quality (or any other) difference ?

Recompression via a lossy algorithm probably

Re: Cheap HDMI capture for Linux

#53

Post by djsumdog »

gcb0 wrote: post #44
jamesfmilne wrote: post #7

You can also use devices that are USB Video Class (UVC) compliant, thus which don't require any drivers. libuvc can be used to capture from these devices: https://github.com/ktossell/libuvc You can get cheap off-brand UVC USB grabbers, or you can get higher quality gear, like the AJA U-TAP: https://www.aja.com/en/products/u-tap Admittedly though I haven't seen anything that comes close to £45 :-)

there's a reason the Starts with "cheap". all solutions so far cost well over what most people paid for their computers or TVs. there was pro composite capture under 200 for a long time. and cobsumer ones for 30ish. and thats dealing with analog. hdmi without DRM should produce even cheapers devices, but yeah, everyone has to embrace DRM to name it hdmi

The UVC one mentioned looks to be in the ~$400 USD price range, which is a far cry from the $800 stuff the article author looked at, but it's still more expensive than the Was that $300~$400 worth the time needed to reverse engineer the cheaper solution? It's all about tradeoffs really. At least it's open source so other people can use it now without the time involved. Also if you need to read in from 5 ~ 10 cameras, the cost can grow very quickly.

Re: Cheap HDMI capture for Linux

#54

Post by phkahler »

benjojo12 wrote: post #14
0942v8653 wrote: post #4

What about HDMI DRM? Does it break it (illegal) or fail when it is used?

This device happily decodes HDCP. I figured the manufacturer does not care

>> This device happily decodes HDCP.

If used as intended will it allow an HDCP source to show on a non-HDCP display? Because stupid AppleTV won't allow "protected" content to display on mt main TV because it doesn't support HDCP, and if you buy something on iTunes you don't find out until you've already purchased it. DRM is driving me away from services like that and I'd rather just stop using them than buy another TV.

Re: Cheap HDMI capture for Linux

#56

Post by samtho »

This quite interesting, I've been toying with building a capture box myself for presentation/gaming streaming and recording. It takes two inputs: HDMI-in from monitor, and HDMI/Other Digital for the camera, and one output: HDMI out back to the monitor. It can be configured to record to its internal SSD or stream (to popular streaming sources). I run a meetup and would love an easy way to record talks, there isn't much out on the market currently which is unfortunate. I'm really happy to see stuff like this surface in the OSS world.

Re: Cheap HDMI capture for Linux

#57

Post by ambrop7 »

riskable wrote: post #51
rsync wrote: post #50

"These units are not perfect for quality, however they are not bad at all, Here is a screenshot taken on my laptop..." I am confused by this ... HDMI is a digital interconnect and deals in digital I/O ... in my mind, if you succeed in capturing that HDMI, the resulting stream should be identical ... why would there be a quality (or any other) difference ?

Because they compress the video before sending it over IP. Nothing fancy, just M-JPEG which is basically the same thing as taking a screenshot of the video every nth of a second and saving it as a high-quality JPEG (probably around 95% quality rating). The screenshot in the video suggests 1000fps but that figure is highly dubious. It is much more likely to be 30 or 60fps on a cheap HDMI->IP converter like this.

1000fps, what the hell? HDMI only supports up to 60fps (which makes sense considering the intended use is sending video to a display device like monitor/tv/projector).

Re: Cheap HDMI capture for Linux

#58

Post by georgemcbay »

warmwaffles wrote: post #55
hacker42 wrote: post #17

Are the gamer HDMI capture devices expensive because they have a low latency? (Besides the verticality of the market.)

Any capture devices you know that are decent? I've been toying with getting one to do demos.

I use the AVerMedia Game Capture HD 2 to capture HDMI from Xbox One and PS4 and I've been very happy with it.

Unlike a lot of such devices this one is stand-alone, I don't plug it into a PC, I just use it as an HDMI pass-through, plug a USB3 external hard-drive into it (it also has a bay for internal 2.5 SATA HDD, but I use an external drive so I can just pull that out of the capture device, plug it into a computer to get the captured mp4 files over quickly and easily for editing).

The stand-aloneness of this device is pretty great because it means you don't need to muck around with drivers on your other computers, though YMMV depending upon specific usage, a lot of people like to do live streams directly to places like twitch and this device isn't really well suited for that sort of thing.

Also, this device (AFAIK) doesn't do HDCP pass through. Game systems generally don't enable HDCP during gaming (but do during, say, blu-ray playback). So that certainly makes it less flexible than solutions which will allow HDCP capture.

Re: Cheap HDMI capture for Linux

#59

Post by jandrese »

Does this work with encrypted video? The sample image came from an unencrypted source, but it seems like a big violation of the HDMI spec if these IP extenders strip the HDCP off before blasting the data over an IP network.

This could be a rather major caveat to this solution if it only works on unencrypted sources.

Re: Cheap HDMI capture for Linux

#60

Post by JonathonW »

gcb0 wrote: post #44
jamesfmilne wrote: post #7

You can also use devices that are USB Video Class (UVC) compliant, thus which don't require any drivers. libuvc can be used to capture from these devices: https://github.com/ktossell/libuvc You can get cheap off-brand UVC USB grabbers, or you can get higher quality gear, like the AJA U-TAP: https://www.aja.com/en/products/u-tap Admittedly though I haven't seen anything that comes close to £45 :-)

there's a reason the Starts with "cheap". all solutions so far cost well over what most people paid for their computers or TVs. there was pro composite capture under 200 for a long time. and cobsumer ones for 30ish. and thats dealing with analog. hdmi without DRM should produce even cheapers devices, but yeah, everyone has to embrace DRM to name it hdmi

> hdmi without DRM should produce even cheapers devices, but yeah, everyone has to embrace DRM to name it hdmi

Not really. HDMI capture devices actually can't "embrace" DRM; no (legitimate) HDMI capture device is permitted to decode HDCP at all since that would defeat the point of HDCP.

HDMI capture devices are expensive because it really is difficult-- 1080p is a lot of bytes per second to decode, reencode, and record to permanent storage.

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