Recording & Streaming your event – Screen Capture 3/7

This is the third article on the “Recording and Streaming your event”.
In this post, I cover details of the screen capture.

Table of content of the series:

Screen Capture

Slightly more straight forward because I assume you get an HDMI feed from the speaker’s laptop. Each speaker should ensure they have the right converter dongle for their video output, but be clear well in advance about your expectations, and have spare adapters anyway. With the rise of USB-C only in ultra-portable lapotos, many haven’t bought (or brought) the USB-C to HDMI adapter to your event.

HDMI is easy, because it’s a protocol without too much variables. Things evolve, so make sure you keep an eye on the subject in the next few years though, with the rise of Ultra HD and new bandwidth requirements.

Where things varies, is where things can go wrong if you’re not prepared. So here’s the minimum to look for:

  • Projector Resolution (and its aspect ratio)
  • Speaker’s Laptop resolution when projecting
  • HDMI capture card resolution (and FPS) & HDCP capability (or lack of)
  • HDCP (Content protection when coming from a Mac, but probably also XBox, PS4 & other)
  • HDMI Matrix, splitter, repeater and other in-line processing devices the venue or yourself may have

Projector Resolution

It’s good to make sure what’s supported by the venue or equipment you will be using. Nowadays, all venues should be supporting resolutions of 1920 * 1080 pixels on a 16:9 picture aspect ratio, but it’s worth making sure that’s what you get.

Some projector supports resolution up to 4K, but I doubt it’s of any value for the audience if your displaying code or PowerPoint. The biggest problem is probably if you get a resolution or aspect ratio that is not supported by your recording device or projector. It can either stop working completely or record something cropped without you realising it until it’s too late.

Always ensure that the HDMI input going into your capture device is of a supported resolution, and do a test recording after each room setup.

If you don’t enforce (whether by process, configuration or device) the right resolution for your capture device, you may need a down-scaling (or up) device, like the Decimator (see below).

Even if your capturing device supports higher resolution, leaving the down-scaling task to your laptop will consume a fair amount of precious CPU cycle.

Some splitters (i.e. the ones mirroring 1 input, into two outputs), are recognised as a monitor with a maximum resolution of 1920×1080 pixels to the OS. In those case, nothing else to do.

Capturing the screen from the presenter’s laptop

Keep this in mind as a backup or last resort: You can ask the speaker if they’ve got a way to record their screen with an app, such as Camtasia or OBS. Make sure they also record the audio even if you have it covered, because it will help you synchronise the tracks in post-production based on the audio.

But that approach goes against the rule to “avoid the need for post processing”.

Because you have to make sure every speaker has the software installed and configured, it’s too unreliable to rely on this for an event with many sessions and speakers.

There are other things you could try, like using the NDI protocol or RMTP to send the capture to another device doing the mixing, but that’s advanced, and I’d consider it hacky.

HDCP & HDMI Splitter

When a Mac projects any video content over, HDMI (also via USB-C’s Display Port Alternate mode), it automatically protects it with HDCP. There are, to my knowledge, no way to disable this. Make sure you are aware, and test your equipment with Mac owners as early as possible.

acelink.jpgThe problem is that the HDMI capture devices (such as the LGP2 or others I’ve tried) don’t support recording HDCP (by design). For you and the presenter, that’s undesired and frankly annoying.

That said, a some useful and cheap little device, an HDMI splitter, can be used to strip off the content protection from the signal, so that it can be recorder. The problem, that’s usually an “unofficial” and not well appreciated “feature” for HDMI devices, who are meant to buy a license for implementing HDMI hardware. Be careful, NOT ALL SPLITTERS WORK.

For us mere mortals, that means one same model from a vendor can have a batch that strips the HDCP and another batch that don’t, depending on the internal chip being used. The same model can have internal re-design that are not necessarily advertised…

I’ve bought an Acelink HDMI splitter 1×2 that always worked with Mac so far, but I can’t find the same on Amazon at the moment. It was only doing 1080p at 30 FPS, so I’ve tried another one meant to support 4k@60fps but it did not strip HDCP. I guess it’ll take some research (google & forums) and try outs to find out the right one, or mod an existing one

The Decimator

decimatorIf you’ve got the budget for it, you should know about this nifty little device packed with lot of features. I don’t own one yet, because that’ll set you back £300/$300, but I can definitely see the benefits of owning one, and I’ve seen it in action.

First of all, it’s capable of up-scaling or down-scaling whatever input you ‘re receiving. With this you can get a consistent 1080p60 no matter what the input you get. This is especially good when you might get different frame rate or resolution depending on the presenter’s equipment, and without your mixing software needing to use your CPU to do the work.

I’ve heard (but not tested personally) that this device can remove HDCP as well, so you could also use this device to inline from the presenter’s laptop to your recording device to avoid the issues mentioned earlier.

Lastly, it can convert an HDMI signal to SDI, which is the standard for professional AV recording (with BNC connectors). HDMI cables usually can’t be carried for longer than 8 or 10 meters without a repeater, while SDI can run for 100’s of meters. The downside is you need a different capture interface, a SDI to USB capture device, for this to work in this context, but they do exist.
As I’m only dealing with consumer-grade equipment given my tight budget, I stick with HDMI inputs and devices, despite the “close range” constraint.

AverMedia Live Gamer Portable 2

This device served us well, but I’ve been getting some issues with them recently, maybe because of their age, or because they’re a bit temperamental with the USB bus.

Another pain point I found is when using it with the OBS software, we sometimes loose the feed and need to “reset” where a source is coming from. This happens when a source is disconnected/reconnected, such as between sessions, and may be down to the software, not the LGP2. It is, nonetheless annoying, and seems more frequent with the LGP2 than with the CamLink.

If you don’t have or want to use a splitter, the LGP2 or LGP2+ (£160/$160) is what you need, because it has HDMI pass-through: you can plug the HDMI out of the LGP2 to the projector without latency.

It’s worth noting that there are two versions, the LGP2 and LGP2+. The LGP2 supports 1080p at 60 fps, while the LGP2 supports up to 4K at 60 fps. The PSConfAsia organisers own the LGP2, so that’s the one I’ve tested.

I really like the fact that those devices can record on micro SD card, OR via a connected PC, unfortunately, they can’t do both and that’s a shame. They are USB powered, and small enough to be practical. They also have audio inputs which means in theory you could mix-in and record some audio, but I’ve not tried them. They come with a long enough USB cable so that you can have them on the lectern with the presenter’s laptop, while connected to your recording computer on a table next to it.

It’s worth noting that you can’t connect multiple of these devices on the same USB port, because they’re using too much bandwidth to be on the same bus. So the USB hub is not an option.
That said, you can use two devices, one capturing a screen, and another one to capture the HDMI clean output of a consumer camcorder for example (I’ve tested it).

This is my new favourite HDMI capture interface, mainly because it’s tiny, light, stable and at a decent price, supporting 1080p at 60 FPS, or 4K at 30 FPS (£120/$115).

This is a fairly new device (the CamLink 4K is from 2018 iirc), and simplistic. It only has HDMI input, and a USB “out”. So it simply transform an HDMI signal to “Webcam” compatible signal.camlink

Because it does not have a HDM pass-through, you must have an HDMI splitter to be able to send the signal to the projector as well. If you add-up CamLink + HDMI Splitter, in the end it’s roughly the same price as the LGP2+, but you only get HDCP stripping if you get the right HDMI splitter.

As advertised, and similar to the LGP2, it works well with a consumer camcorder that outputs a clean HDMI signal. For PSDayUK 2019, in the main track we were using two CamLinks 4K, one for the screen capture, and one for a camcorder filming the speaker.

Too bad the HDMI splitter is a bit of a gamble, but you can still use them with this capture device. The problem with adding in-line devices is that you increase the number of single point of failures, and need to power more things.


Another device I haven’t tested but heard great things about is from the Magewell brand, such as the USB capture HDMI 4K plus. It has HDMI loop through, HDMI Audio extractor and mic input, supports 4K 60 FPS, but can go up to ~1920×1080 YUY2 90fps, which is great if you’re capturing game content. USBCaptureHDMI4KPlus_1What’s limiting here is the speed of the USB 3 bus, but if you’re thinking about streaming, you either won’t be able to stream at that resolution, or viewers won’t be able to watch at this quality. At least for now.

It also has some video processing capabilities built-in, so you don’t have to use CPU cycles for up-scaling or down-scaling your input. It’s not as powerful as the Decimator, but can probably do a good job of the simple tasks.

The Magewell devices do not capture HDCP protected content, as required by law/regulations/licenses, so if you need to capture what comes out of a Mac, you’ll still need something to strip off HDCP. If you do so using an HDMI splitter, that will most likely limit your resolution and framerate. If you’re using a Decimator, then do you can select the output and you may not need the Magewell.

I guess I’ll only know when I’ve played with it (Magewell, if you read this… 😉 )

Screen Capture Conclusion

If your intent is purely to capture the screen for recording and/or streaming an event, and you know you’ll use an HDMI splitter that may limit the screen resolution, then the Elgato is probably the best value for money, especially if you know the next evolution will be to buy a Decimator.

Keep in mind that some HDMI splitters and devices will detect and align to what’s connected on their port 1, and pass the characteristics to other devices.

As an example, when my CamLink 4K is connected to the output 1 of my 4K 60FPS HDMI splitter, my laptop connected on the input of the splitter detects a “CamLink” device (not the splitter). My monitor, an LG38WL95C, won’t be able to be used at its maximum resolution. Most likely I will be limited to the aspect ratio and resolution set by the splitter, or the CamLink, whichever is the smallest. Or it will just not work until you lower your resolution.

If I use my AceLink splitter connected the same way, the splitter exposes a “Dell” monitor of some sort, with limited resolution (1080p @ 30 fps). That’s because this old acelink uses a receiver chip, before repeating the received signal. That’s probably why it strips the HDCP protection, instead of doing a “pass through” where the laptop will negotiate (HDMI handshake) with the actual receiver, in my case the Camlink. As I said before, stripping the HDCP signal is not compliant with the HDMI license the hardware manufacturers need to follow to market their devices as “HDMI”, and doing so exposes them to have their license revoked.


NEXT: Filming the Talent

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