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"220, 221, Whatever IT Takes" – on Frame Rate Conversion, Video Production, and iMAG

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"220, 221, whatever it takes" – on Frame Rate Conversion, Video Production, and iMAG


This is an old movie reference from Mr. Mom (1983, starring Michael Keaton & Terri Garr) where Keaton's character is queried about the wiring he is adding to his home. When he smugly blurts out "220, 221, whatever it takes," he reveals his abject absence of knowledge and skill in home remodeling — and especially wiring — while the person he tries to impress works to stifle his giggles. (watch the clip)

Today, we are deluged with terms which are used interchangeably to the great peril of the functionality of the video portion of today's church tech facilities. Specifically in this post, I will deal with "Frame Rates."

Once the NTSC standard was adopted, introducing color into the old 60Hz power-line-locked TV system, the frame rate for North American television systems was slightly changed to 59.94Hz to mitigate some interference patterns in both audio and video caused by the injection of the color information into the broadcast. That was a very, very long time ago. Interestingly, when ATSC digital transmission was introduced to eventually support HD, the opportunity existed to nudge the 59.94 fractional frame video world fully into 60Hz. Indeed, it's true that 60Hz frame rates are supported by the ATSC standards. But because there was so much 59.94Hz material in archives, and a lengthy transition from analog to digital, most chose to adhere to the 59.94Hz frame-rate standard just to alleviate the need for frame rate conversions in production and in the set-top boxes feeding older TVs.

So, what is up with this today?
When moving from an all computer-based A/V system (i.e., a lyrics computer which also plays back videos) to one integrating inexpensive "security" PTZ cameras, there is usually no difficulty, as most of those cameras deliver 60Hz by default, especially if they do not natively incorporate a BNC video SDI connection. The "A/V" switchers in this range mostly include scaling, synchronization, and frame-rate conversions to simplify deployment of these small systems.

However, quite the opposite is true when a "traditional" broadcast-type video facility operating at 59.94Hz starts incorporating the "big-bang-for-the-buck" security PTZ cameras, computers, and point of view (POV) cameras, which are typically set for 60Hz.

The "broadcast" production switcher may be able to switch an all 60Hz program, but when it is set to 59.94Hz to accommodate all the existing "broadcast" pieces of equipment, it cannot "rate convert" to accommodate the 60Hz sources.

Some manufacturers are not helping the matter
Many broadcast gear manufacturers indicate "60Hz" when they really mean "59.94" likely because someone cleaning up copy thought it would be a good idea to round up. Some computers indicate their "refresh rate" as "NTSC" (which has always been 59.94Hz analog composite) and compound the error by using "NTSC" as a description for their HD outputs — which happen to actually be 60Hz.

These errors are widespread as there are differing specs for the same product depending on where the specs appear: web pages, price lists, spec sheets, manuals, and applications notes. It takes some product history and industry experience to successfully navigate this confusing mess. And even then, one can be caught by surprise simply by how a product is "spec'd."

Encounters with the 60Hz vs 59.94Hz domains
In this environment of unsure specifications, Houses of Worship are particularly vulnerable to this frame rate clash due largely to the heavy influence of videographers accustomed to single-camera productions where frame rate incompatibility issues are rarely encountered. Single camera videographers are most familiar with frame rates in the context of achieving a particular "look," and their settings are therefore largely irrelevant from a systemic viewpoint since they are operating as "islands."

Today's church tech video production systems can be very complex things, driving iMag screens, recorders, live streaming devices, and alternate feeds to peripheral displays, and even on-platform monitors or walls. The video source devices will often be various types of cameras (systems cameras, PTZ cameras, and POV cameras) along with various computers and hardware for graphics generation and video playback. It is exactly this mix of products from different lineages which creates the opportunity for chaos at implementation.

You've seen it before, the Lyrics computer or POV camera is fed into a converter feeding an SDI monitor, and it looks great. But, it either breaks up frequently at the switcher, or it doesn't show up at all.

Directly addressing the issues
So, for efficiency , cleanliness of the install, and for long-term stability, whenever possible, the sources brought into the complex system must be set to the same resolution and frame rate to be used without boundaries throughout the system. But in reality this is far more difficult than most realize.

Grass Valley and several others produce products and solutions to manage these conflicts where the devices cannot produce the functioning frame rate of the system, and/or its resolution. For most churches, the simple "brick" or "throw-down" devices are technically and visually suitable, and choices are often price driven, but pricing should never be the first "filter" for purchases.

In this "throw-down" space, one must not go too far down in price as there is a clear technology/barrier risk.

The three types of HDMI-to-SDI converters
The least expensive devices are simply "cable extenders" designed to feed a monitor with a complimentary device on the other end. Converting HDMI to SDI is only a "signal transport format" change — from an HDMI cable to coax. That alone is usually not enough to let a POV camera or a graphics computer be integrated successfully and RELIABLY into the video production system. So, especially for churches, these are rarely a viable solution for converting computers and POV cameras into a multisource video production.

The next step up in price are converters which include "scaling" and/or "frame-rate conversion" features. These devices, depending on design and cost, will send the incoming computer or POV camera into a frame buffer which is read-out at a rate based on an internal clock, or potentially by the source video. These devices, which are vastly more complex than "format converters," are also much more expensive. They work well when the video production switcher to which they are directly connected includes an on-board synchronization function on those inputs.

The top level in price are those converters which, in addition to including "scaling" and/or "frame-rate conversion" features, also include "synchronization." These devices use a frame buffer to temporarily store the incoming computer or POV camera which is then read-out at a rate based on the "System Reference" to which the rest of a professional system would normally be locked. These devices add a bit more cost to those converters which can scale and rate convert, but are also the most likely to give the enduser the reliability they need.

The use of the converter/scaler/rate-converter/synchronizer allows the resulting SDI signal to be treated as any other "systemized" signal, including being routed synchronously when the facility is large enough to include a video routing system independent of "AUX busses" on the video production switcher.

While demonstrating these devices at InfoComm, many attendees seemed surprised at the capabilities of the more expensive devices. One person was the Service Manager for a regional System Integrator. After his demo, he said he would mandate the specification of this particular device to all his sales representatives as the inexpensive format converters were costing them huge numbers of man-hours (and obviously $$$) per job in service tickets.

So, in short, let extenders be extenders. However, remember — just because that digital video is travelling on coax doesn't mean it's compatible with your system. Signal conversion is very inexpensive, but making it work reliably as part of a system costs substantially more — every time.

- Joe

About the Author
Joe Paryzek has been active in church production technologies since 1977 in full-time, part-time, and volunteer positions. He has also been actively involved with TV trucks, sports, and other live event coverage for decades. After his 27 year tenure with Grass Valley, Joe is now at Diversified (formerly Technical Innovation's Blue Hat Design Group) where he performs needs assessments, functional analysis, systems design, and technical sales support.

 Comments 
Wed, 28 Jun 2017 06:15:28 PDT
CHinkl... wrote:

Explain the dreaded HDCP problem when inserting that into your HD-SDI system.


Response:

HDCP is intended to secure commercial video from piracy by allowing that material to be displayed… only — by preventing copying of that content as it travels across connections. So, professional signal processors, video switchers, and even recording devices with, for instance, HDMI inputs will "blank" or show "no signal" when connected to a source device which is "expecting" to be connected to a bona-fide display. Professional video devices do not allow HDCP encrypted material to be utilized, period, because of the risk for pirating.

That said, many users of devices with HDMI outputs make the assumption that professional video equipment with HDMI inputs MUST be able to utilize the content. In the context of this blog post, there are many issues between resolutions and frame rates (at the very least) which get in the way of this actually working. However, this is under the assumption that the content coming from HDMI is legitimately "owned" by the user — in other words, "originated" by the user so that there wouldn't be any HDCP issues.

Unfortunately, some commercial and consumer media players will treat owner-originated material as HDCP encoded, and therefore the downstream professional video equipment to process, switch, or extend via SDI simply will not work, even if all the video standards were compatible. When all else fails at this point, using a player with HD component analog outputs is required, and a supporting HD component analog to SDI converter/synchronizer would be required. These are becoming extremely rare as the last vestiges of analog disappear.

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