While we will explore encoding and modulation in Chapter 7, we will now touch on digital video encoding in this chapter.
Just like NTSC (National Television System Committee) before it, engineers developed another standards committee. Yet this time they joined with Motion Picture (movie) engineers, and created SMPTE (Society of Motion Picture and Television Engineers). The society is responsible for writing the standards you and I will live by in this industry.
In the standard-definition field, when researching SMPTE standards, you will be looking for SDI (Serial Digital Interface) standards. In the United States, this standard basically involves data rates between 143 Mbps and 360 Mbps. On-screen ratios may be 4:3 or 16:9.
In the high-definition field, these same SMPTE standards will be called HD-SDI (High Definition Serial Digital Interface) standards. And in the U.S. This standard has a data rate of about 1.485 Gbps (mistakenly called 1.5 Gbps) for uncompressed, studio-quality HDTV. On-screen ratios are usually 16:9.
compression.
Many stations, online companies, consumer products, and even broadcast-quality gear sold today uses MPEG-4 compression. But I can say, without apprehension, that there is still no standard for MPEG-4. Buying any product that records or transmits in MPEG-4 means needing a device or software to play back or receive that MPEG-4.
You need to be aware of this issue. For if you buy an MPEG-4 device from a company like JVC, for instance, and the playback device breaks or becomes corrupted, you probably won't be able to get it out with a SONY player. You may not be able to playback the video with a new JVC device if that company no longer supports the old MPEG-4 standard.
The same issue occurs when companies buy MPEG-4 encoding equipment and discover they can no longer buy receiving equipment that recognizes the encoded feed. New equipment may not be backwards compatible, and after a few years a company may no longer support its old equipment if chipsets inside are no longer available. You now own an expensive boat anchor.
There are other problems being ironed out with MPEG-4. There is more “latency” or delay in the encoding. There have been up to ten-second delays in test-loop mode in some practical tests done by engineers at the networks. The quality over 12 Mbps starts to deteriorate over MPEG-2. At 20 Mbps,
MPEG-2 looks better. But MPEG-4 will likely show up in broadcasts requiring very little bandwidth at very little power.
When researching new equipment, don't be pulled in by smoke and mirrors. Find out what you can about the playback of certain equipment. If you should be in the field and a playback unit breaks, will you be able to borrow from a neighbor and send your video with their device?
Most of the equipment made for terrestrial and satellite transmission today adheres to MPEG-2 standards.
On the ground, from local TV stations to your new HDTV set, HDTV systems in the United States were designed to deliver images at nearly twice the vertical and twice the horizontal resolution of SDTV (standard definition TV). The original bandwidth, 6 MHz of analog video, will go away in a big switch on February 2009.
Stations soon discovered they had choices. They have 6 MHz to use for HDTV transmission, or as some discovered they could continue to send one SDTV signal and up to four more SDTV signals in that same amount of bandwidth.
The reason I go over this is because you will see this in satellite transmissions. If you take the time to figure out what each empty hump really is on each satellite transponder, you would discover computer data from banks and financial institutions, MUXes each transmit an MCPC signal and each is capable of carrying a dozen television stations and radio stations. You might also find a whole transponder carrying only one HDTV signal, perhaps a football, basketball or baseball game.
This is the same way terrestrial television transmission works, and quite frankly the way most of the broadcast world works. There are many standards out there, and yet there are no standards anymore. You will find this frustrating, and yet comforting at the same time. If it is important for people to find your signal, be sure to update your transmission “descriptor” in your encoder's setup menu. This basically describes what you are transmitting, where, the downlink frequency, and other information. It might even include your phone number (in place of what used to be called an analog “ATIS.” We will discuss this later.
The ATSC (Advanced Television Systems Committee) was another off-shoot of the former NTSC. They basically are a U.S.-based committee advocating MPEG-2 video and Dolby Digital AC-3 audio.
would be the 18 formats or standards for television in the U.S.
However, the FCC rejected some of their work and sent them back to the drawing board. Their work hadn't included 25 or 50 Hz frame rates, which left out and didn't take into account movie and computer industry standards.
There isn't enough paper in the world to write up everything NTSC, SMPTE, ATSC or the FCC have to say. And it's just too much to include here. But use what information I have given you to look for more information about these committees and the incredible work they have done for all of us. Consider this book the gateway to the knowledge available to you. Don't let your learning stop with this book!