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Inexpensive HDMI capture sticks solve camera shyness types 1, 2 & 3 in many cases

Allan Tépper

For under US$20, these new —often unbranded— HDMI capture sticks have flooded the market to “compete” with the renowned Elgato CamLink 4K which officially costs ≈US$130 but has become scarce and the victim of price gouging. In fact, in many streaming situations, these two models I tested —which each now cost under US$20— are often better when 1080p (or 720p) streaming is appropriate even though a local 4K UHD recording may be desired too. These inexpensive HDMI capture sticks can indirectly solve type 1, 2, & 3 camera shyness while the more expensive CamLink 4K can only solve type 3, with a caveat that most people won’t mind after they see (or don’t see) its impact (or non impact) on the visual experience.

 

In this article:

 

Refresher about the three types of “shy” 1080p camera situations

There are three types of 1080p shyness in cameras, in order of importance: PsF, Telecine and Doubling.

Type 1: PsF (progressive segmented frame)

I am separating PsF (progressive segmented frame) into three subcategories:

  1. When the shy camera is set to image (and sometimes also to record internally) with a common progressive framerate (in ex NTSC regions) like ≈29.97p, it sadly outputs the signal as PsF (progressive segmented frame), in other words, disguised as ≈59.94i. To be more specific, it takes each progressive frame and segments it into two artificial fields, each with half of the original pixel resolution and each with 540 intertwining lines to add up to the original 1080. Unlike true 1080i —where each field can potentially have different temporal (time) information when there is movement, with PsF the temporal information of each artificial field is always identical.
  2. Similarly, when the shy camera is set to image (and record internally) with a common progressive framerate (in ex PAL regions) like 25p, it sadly outputs it the signal as PsF (progressive segmented frame), in other words, disguised as 50i.
  3. The third PsF case is very rare nowadays and never happens with HDMI, but only with some SDI and with very expensive cameras, where with the ≈23.976p (aka ≈23.98p) rate the camera sadly outputs the signal as PsF (progressive segmented frame), in other words, disguised as 47.952. (In the case of HDMI, shy 1080p cameras in ≈23.976p use a telecine method with a 2:3 (aka 3:2) pulldown explained ahead.) This rare case is outside the scope of this article.

Type 2: Telecine with pulldown

To make the ≈23.976 fit in a more standard ≈59.94i television rate, telecine performs a complex assignment to make pieces of the original frames “fit” into ≈59.94 fields, some of which contain the same temporal information and others don’t.

 

This is illustrated in the above graphic, which I created in 2008 to illustrate my very first article in ProVideo Coalition magazine. The instructions for the pulldown (i.e. “Put the first progressive frame in both fields of the first interlaced video frame. Now, put the second progressive frame in both fields of the second video frame in the first field of the third video frame, then…”) seem as twisted as the Twister game which dates back to 1966.

Type 3: Doubling of progressive frames per second

When set to image and record ≈29.97p, some shy 1080p cameras duplicate the number of frames per second to ≈59.94 progressive frames per second on the HDMI or SDI output. Similarly, when set to image and record 25p, they duplicate the output framerate to 50 progressive frames per second over HDMI or SDI. As long as your hardware can accept high progressive framerates like 1080/50p and 1080/≈59.94p (i.e. more recent models like the UltraStudio Recorder 3G, ATEM Mini, ATEM Mini Pro, ATEM Mini Pro ISO), this is the easiest type of shyness to solve, and doesn’t require the video mixer (“switcher”) developers/manufacturers to do anything special, as several already have at my request to properly resolve PsF and telecine while retaining all of the original image quality. To solve type 3 shyness, the user/operator should simply set the camera menu and the session in the video mixer for the desired delivery framerate (1080/25p or 1080/≈29.97p) and the mixer or software will simply skip half of the repeated progressive frames per second. This solution is not perfect, but has been the best way to solve type 3 shyness when your camera suffers from it, until the other solution proposed ahead in this article, which can also solve all types: 1, 2 and 3.

The reality of streaming in 2020: Why not stream 4K live…

Even though many available cameras offer 4K UHD, in most cases in 2020, it’s not feasible to live stream 4K UHD yet (even if you really wanted to do that). This is both because of bandwidth issues (your Internet upload speed) and platform capabilities. I’ll cover some popular services in alphabetical order:

Often in 2020, we simply want to stream at 1080p or 720p, without any local recording or ISO recording. Other times, we want to record 4K UHD locally but live stream at 1080p or 720p. In either case, it is often too demanding on a single computer to receive and then downscale from 4K UHD to 1080p (or lower) while also performing other tasks (i.e. switching cameras, connecting remote video guests, picture-in-picture, adding lower thirds, chroma key) so it would be better to send the signal to the computer already downscaled to 1080p by performing that task externally of the computer.

Although many 4K UHD capable cameras can indeed supply a pre-downscaled 1080p signal, sadly many of them are still shy with the 1080p signal, as explained earlier in this article. In other words, they don’t output the original native framerate as we really need it, but instead complicate things by either doubling it (type 3 shyness) or as a quasi-interlaced 1080i over ≈59.94i or 50i (type 1 or 2 shyness).

Fortunately, since in 4K UHD there is no such thing as interlaced video, even those camera manufacturers who love to make their cameras “shy” when outputting 1080 have been forced to make them “outgoing” when outputting 4K. So when these cameras output a signal like 4K UHD at ≈23.976, exact 24, exact 25 or ≈29.97 fps, there is no longer any possible confusion of it being interlaced, since it’s undoubtedly progressive at its original native framerate, without pulldown or doubling, since the manufacturers know that all 4K UHD monitors can accept the native rate. That’s where (for this particular purpose) the new inexpensive HDMI capture sticks can shine even more than the higher-priced CamLink 4K from Elgato, which passes through the native 4K UHD signal as received. Why? Read the next section 🙂

These inexpensive HDMI capture sticks downscale 4K UHD to 1080p in hardware, although with a tiny caveat

As explained in the prior section, although for non-streaming purposes, you might want your 4K UHD signal to enter in your computer as is, if your main reason to sending it to computer in 2020 is to stream it live, it makes more sense to send it already downscaled to 1080p to alleviate your computer and your software, i.e. Ecamm Live, (covered in many articles click for a free trial) to later feed any of the platforms discussed earlier via the Virtual Cam feature in Ecamm Live Pro. It’s enough work to have your computer encode the streaming signal in real time. Alleviate it by downscaling the 4K UHD in external hardware for under US$20. That’s exactly what the two models I tested do, since their USB output is fortunately limited to 1080p.

Before explaining the tiny caveat (which probably won’t bother you for this application), I’ll first share some examples I captured at 1080p at ≈29.97p from Francisco Javier Arbolí’s Sony PXW-X70 camera (which suffers from type 3 shyness at this framerate when outputting 1080p over HDMI or SDI, but fortunately is not shy at all when outputting 4K UHD over HDMI) onto Memo Sauceda’s MacBook Pro. NOTE: All videos in this article are silent. All were imaged in the PXW-X70 at 4K in the same room but on different days, downscaled by an inexpensive capture stick, recorded at ProRes422 at the matching incoming framerate and later trimmed.

As covered before in past articles, when Sony says “30p” in cameras under ≈US$5k, Sony really means ≈29.97p. Exact 30 fps hasn’t been a broadcast standard rate since before 1953.

Did you notice any missing frames in the above clip? I didn’t either when watching it at normal speed, but I was surprised to see in the metadata that they both seemed to capture at 1080p25 (25p is a standard framerate in ex-PAL regions) instead of ≈29.97p. The same thing with the two different ones I tested. At first, I suspected that maybe these two inexpensive HDMI capture sticks were providing erroneous metadata. However, after further investigation (as you’ll see ahead), they are both actually converting the ≈29.97p signal to 25p by removing four (4) non-sequential frames. I confirmed this by later setting the Sony PXW-X70 to display free-run, non-drop frame (NDF) timecode onscreen and then playing back the recording frame-by-frame.

Although Vimeo’s compression and player sadly don’t allow us to advance every individual frame (even when using Shift + right arrow or left arrow), on my computer when playing the original ProRes 422 file (which is CFR i-frame compressed, meaning every frame is complete unto itself) frame-by-frame, I see that frames 2, 8, 14, 20 and 26 have been removed to convert the original ≈29.97p into 25p, but it is fortunately not noticeable when playing at real time, even with the continuous movement of an oscillating fan. Both units do the same removal of five frames, despite the official description of one of them which states that it delivers up to 30 Hz.(Of course, everything was shot with the shutter set for 180 degrees.)

Next, I wanted to test how these two inexpensive HDMI capture sticks would behave when actually setting the camera to shoot at 4K UHD at 25p. Here are the results:

Above, the 25p 4K UHD source video recorded with the Amazon-brandless unit.

Above, the 25p 4K UHD source video downconverted from 4K UHD to 1080p with the Walmart-GeweYeeli unit.

Both units fortunately passed all 25 frames, without skipping any. So when feeding these inexpensive HDMI sticks with 4K UHD at 25p, they pass the native 1080p25 signals.

Next, I wanted to test how they would behave if I sent 4K UHD at ≈23.976p:

Above, the ≈23.976p source video downconverted from 4K UHD to 1080p with the Amazon brandless unit. In cameras under ≈US$5k, when Sony says “24” in a menu, Sony means ≈23.976. Starting at about ≈US$5k cameras, Sony begins to offer both exact 24 and what it calls 23.98, so with those, Sony has no choice but to be more accurate in the menu.

Above, the ≈23.976p source video downconverted from 4K UHD to 1080p with the Walmart-GeweYeeli unit.

Both added an extra frame to make them be 25p! The unbranded Amazon unit repeated frame 17 consistently, while the Walmart-GeweYeeli unit repeated frame 16 consistently, so apparently they don’t share the same chip. Now we know that these inexpensive capture sticks are 25p exclusive, although each one is repeating a different frame. Fortunately, the additional frame is not noticeable when played at normal speed.

Fascinating conclusions

These inexpensive HDMI capture sticks do an amazing job of down-converting 4K UHD signals to 1080p when that’s the maximum spatial resolution you are going to live stream anyway. The GeweYeeli model from Walmart has the advantage of an HDMI passthrough (i.e. to feed a local monitor or monitor/recorder), although it requires external power. The Amazon unbranded model has the advantage of being more compact and not requiring external power, since it is USB bus-powered. They both indirectly solve all three types of camera shyness (1, 2 and 3) as long as your camera can output 4K UHD over HDMI. This means that they both indirectly prevent your software from unjustifiably de-interlacing an already progressive (albeit disguised) signal. That’s great since you’ll conserve all of the spatial resolution (1920×1080), rather than sacrificing it by omitting a field (leaving you essentially with only 1920×540) or running it through a more complex “coffee grinder”.

The forced framerate conversion explained earlier is fortunately not noticeable to me at normal playback. However, if your cameras are capable of being set to 25p natively (i.e. because it’s a worldcam or because it’s a segregated European version) and 25p doesn’t cause any flicker with your lighting in a 60 Hz country (as was fortunately the case with Memo Sauceda’s professional LED light), be a purist and set your cameras to 25p as long as you are not additionally making a local recording for use on traditional broadcast in an ex-NTSC country (i.e. the United States and most other countries in the Americas). If you do that, then set your Ecamm Live Pro to stream 25p also. On the other hand, if you are making a local recording at ≈29.97p for subsequent traditional broadcast, then indeed set the camera to ≈29.97p. But since we know that the signal reaching Ecamm Live via one of these inexpensive HDMI capture sticks is 25p, set Ecamm Live Pro to stream 25p in any case. It is silly to stream more frames than those that actually exist, since it’s a waste of your available bandwidth budget, which is better served to have less compression on each of the 25 frames per second being streamed.

I am amazed at how well these extremely inexpensive HDMI capture sticks can facilitate accomplishing these essential tasks simultaneously at such a low cost:

The more expensive ≈US$130 Elgato CamLink 4K indeed has its virtues, but not for the explained task described in this article. For live streaming in 2020, these inexpensive HDMI capture sticks do more for us at over 84% savings in cost. Fortunately for Elgato, they are already selling more than then can build, so they shouldn’t be too upset about this article.

Acknowledgements

I thank Francisco Javier Arbolí for lending his Sony PXW-X70 for these tests and Memo Sauceda for lending his oscillating fan, tripod, light and MacBook Pro.

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FTC disclosure

No manufacturer is specifically paying Allan Tépper or TecnoTur LLC to write this article or the mentioned books. Allan Tépper has no financial connection to any of the capture cards mentioned in this article. Some of the other manufacturers listed above have contracted Tépper and/or TecnoTur LLC to carry out consulting and/or translations/localizations/transcreations. Some of the manufacturers listed above have sent Allan Tépper review units. So far, none of the manufacturers listed above is/are sponsors of the TecnoTur , BeyondPodcasting CapicúaFM or TuSaludSecreta programs, although they are welcome to do so, and some are, may be (or may have been) sponsors of ProVideo Coalition magazine. Some links to third parties listed in this article and/or on this web page may indirectly benefit TecnoTur LLC via affiliate programs. Allan Tépper’s opinions are his own. Allan Tépper is not liable for misuse or misunderstanding of information he shares.

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