ASI Muxing

One of the biggest advantages of DVB (digital video broadcasting) transmission is the ability to transmit compressed video in a fraction of the bandwidth required for analog FM video.  While encoding profiles have improved over the years, taking off with MPEG-2 and moving on to the current standard H.264 (MPEG-4) video, the basic transport stream that contains that data has remained the same.  This signal is called ASI, or Asynchronous Serial Interface, which is based on a 270mbps clock, the same as the SD-SDI video interface, which allows it to pass through the same routers that handle SDI video.  While SDI carries uncompressed serial data at 3 common bitrates (270mbps for SD, 1.5gbps for HD, and 3.0gbps for 1080p HD) ASI caries a transport stream of compressed MPEG data.

One of the elements of the transport stream is Packet Identifiers, or PIDs.  There is one PID number for each component of a transport stream coming out of an encoder, commonly there are two- one for video and one for a single audio pair.  More complex streams can add additional PIDs for extra audios, closed captioning, or other ancillary data.

A transport stream analyzer showing the PIDs from a simple encoder.  The PID number is shown, along with its content and total bandwidth on a bar graph.  Here, the audio is 196kbps and the video is 4.2mbps, for a total stream of around 4.4mbps.

Typically, in the news gathering world, there is one encoder per signal on the satellite, known as a SCPC, or Single Channel Per Carrier.  On a busy satellite you may see dozens of these small signals next to each other.  A single truck can transmit multiple SCPC signals for doing multiple video paths.

A device called a Multiplexer can take several ASI inputs from several encoders, combine all their PIDs (reassigning if necessary to avoid duplicates) and output all that on a single ASI stream for uplink.  In the process it can drop PIDs, reassign them to different channels, even rename the channels themselves.   This is known as a MCPC or Multiple Channel Per Carrier signal.  This is the same technology DirecTV uses to transmit their channels to homes, although their muxes take it one step further by dynamically adjusting encoder bitrates based on content for optimal use of bandwidth, using a closed-loop system known as Statistical Multiplexing, or Stat Mux.  There are advantages to both SCPC and MCPC...


A complex MCPC stream containing multiple channels, some with HD H.264 encoding and 4 pairs of audio (8 channels) for surround sound or multiple languages, along with some standard stereo feeds with SD MPEG-2 video encoding, all within the same stream.  A multiplexer allows different kinds of encoded streams- from simple to complex- to be combined on a new stream.  "Unknown" represents newer audio and video encoding methods that this analyzer does not recognize.

A spectrum view showing 4 SCPC carriers on the left, and one large MCPC on the right, which may contain dozens of channels.  Note- the size of a carrier does not necessarily mean its SCPC or MCPC, a full 36MHz transponder of HD MPEG-2 video is a SCPC, and a 9 MHz signal can contain a MCPC of several SD H.264 channels.  An ASI stream analyzer can show exactly what is contained in a signal.  DCI's HD1 satellite truck and teleport have these advanced diagnostic tools.

Both of DCI's trucks and flyaway uplinks are equipped with Adtec DTA-3050 ten-channel muxes.  They are not commonly used in the truck, but they are an excellent tool to have available.  The flyaway however, is designed to use the mux exclusively for multiple path transmission.

Benefits of mux transmission:
More efficient use of bandwidth.  Separate, individual signals must leave space between the carriers to avoid interference.  This is called guardband and is basically wasted space since there is no data being transmitted there.  A single 18MHz carrier will carry more data than three 6MHz carriers with guardband between.  Error correction is also not needlessly repeated.
Linearity.  This is the primary reason we use muxing on the flyaway. As more individual signals are fed into a typical tube amplifier, intermod is generated, which are spurious signals on harmonics of the primary signals.  As more signals are added to the amplifier, more intermod is generated, and the amplifier must be run at a lower power to avoid these spurious signals from causing interference to other users of the satellite.  So a 400w amplifier may only be able to use 200w before the intermod becomes unacceptable.  By using a single signal to carry the required number of paths, the amplifier can be run at a much higher level.  This is one of the main reasons we can operate so many paths off a small airline-checkable flyaway dish.
Less Equipment.  Using SCPC, each path requires a modulator to go with the encoder. The modulator takes the ASI and turns it into a radio signal.  Using MCPC, all the encoders feed into the mux, and that feeds a single modulator.  Of course, for redundancy we always carry a spare modulator, but it saves a lot of space to not need a modulator for every transmission path. 


ASI analysis of a mux carrier from Lousiania PBS.  This mux also contains some data channels.

 

 Disadvantages of muxing:

Availability.  Unlike individual carriers that can be turned on and off on demand, a mux is a single carrier and it is not possible to remove paths without reconfiguring the entire mux and changing the modulator and receiver settings for a new bandwidth.  In a news event, a client may want to add and remove extra paths as the story requires to save money on bandwidth.  Using a mux, that is not possible.  Muxes are best suited for feeds where the number of paths required is likely to stay the same. 

The mux remains a very powerful tool in our kit to allow previously impossible results from our flyaway uplink. Contact DCI to learn how we can apply this and other technologies to your video transmission needs.

150th Anniversary of the Battle of Gettysburg

Last month DCI produced two large multi-camera webcasts for the 150th anniversary of the battle of Gettysburg.  Whether its webcasting a feed from an overseas satellite broadcast, simple one camera webcast to a full-on production with multiple cameras, full graphics suite and playback, DCI can handle any webcast need, no matter how large or small.  Our production in Gettysburg included two cameras for multiple guests, a long-lens camera, bump shot, and even a wide view camera up on a 40-foot mast, all switched in our production uplink truck and fed back to DCI using efficient HD H.264 DVB transmission where it was encoded for the web.

 ATEM 1M/E switcher and audio board for the production setup in the satellite truck.

 The two-camera interview stage also included a monitor for program return, and another showing a multiviewer of all five cameras.

The second day set, which included some rain in the morning.

Setting up a 33x lens and camera on the roof of the truck to capture the reenactment of Pickett's Charge.

Interview with best-selling author Jeff Shaara.

Creating lower-thirds graphics on the fly as guests came on the show.

Contact DCI if you need an event produced and webcast!

3D Live Surgey- first ever!

  

 One of three seperate locations at the San Diego convention center, this is a 3000' seat auditorium with huge projection monitors, which really highlighted the quality difference between our HD satellite feeds and video conference systems. 

Control room for the above auditorium, with the Boxline Box equipment occupying a small corner of the graphics table.  

When most people think of 3D video, big blockbuster movies come to mind.  3D-TV has not really penetrated the home market as quickly as HD for example.  Most of the content available to home viewers is produced content, not live video.  As a live transmission company, producing a live 3D broadcast presented a lot of challenges in uncharted waters.  DCI recently worked with Boxline Box medical communications to transmit the first-ever live broadcast of a 3D surgery at the American Urology Association (AUA) annual convention in San Diego, CA.   While most medical broadcasts are done via videoconference, Boxline's highly experienced Operating Room video staff and DCI's quality-obsessed field uplink engineers combine perfectly to produce the best looking live broadcasts in the medical communications industry.


DCI and Boxline Box have worked together for several years to coordinate the transmission aspects of live surgery broadcasts.  We handle brokering satellite trucks, coordinating space segment, and doing quality-control of the live feeds from our teleport to ensure the highest quality picture possible in the bandwidth available.  Boxline Box handles the OR video production, return audio so the attendees can ask questions of the operating surgeon, and switching the local feed at the convention.  When an event is big enough, DCI will travel to personally handle the transmission.  Such an event is the AUA annual conference, held this year in San Diego, where we downlink three or four simultaneous HD feeds from trucks we coordinate all over the country.


Three separate HD live surgeries. 


The AUA conference includes a lot of live video from the daVinci robotic surgical system, which natively works in 3D for the surgeon doing the procedure.  All the previous feeds we have done were all standard 2D HD, but this year we stepped it up a level to provide the same 3D HD video seen by the operating surgeon. 



daVinci system surgical "tools" including the 3D scope.  The cameras are contained inside the green cylinder and lenses are at the tip of the scope. 

A surgeon controls a live daVinci robot.  There is also an electronic simulator with the same console but the robot arms are virtual. 

Because the data required to carry uncompressed 3D HD video exceeds the 1.5gbps defined in SMPTE-292M, commonly known as HD-SDI, there are two ways to carry this content.  SMPTE 424M is the most simple within a production plant, it uses a single coaxial cable with a data rate of around 3.0gbps.  This interface is commonly referred to as 3G-SDI, although the "G" stands for gigabit, not "Generation" as 3G cellular standards.  The only problem with 3G-SDI is very few HD encoders and receiver/decoders used by satellite trucks and teleports are capable of handling it, and the few that do require expensive license keys which no one has purchased due to the lack of 3D transmission requests.

 Competing for attention was a display of two grotesquely large human kidney stones. 




Testing the 3D HDMI converter with a uplink from DCI that same day.

The second standard is known as dual-link SDI, defined in SMPTE 372M.  This standard is nothing more than two HD-SDI signals running on two cables, one for each "eye" in a 3D video system.  Converting back and forth between 424M and 372M is fairly simple using a converter such as a Matrox MC100.  We can transmit a dual-link signal using two encoders and two receiver/decoders.  Doing two paths is no big issue for most trucks, the issue for a 3D broadcast is both decoded video signals must arrive at exactly the same time.  Slight variation in firmware or seldom adjusted settings like GOP (group of pictures) and PAFF (Picture-adaptive frame-field) can cause millisecond propagation delay (the delay inherent in any encoding/decoding and satellite transmission system) differences that can throw off the picture when both "eyes" are combined on the viewing monitor.   Most compression hardware manufactures have proprietary solutions to time the encoders or decoders with genlock or other methods to make sure the two paths line up exactly.  These solutions are expensive and not practical for most events because they are not standards-based and require matching equipment on both sides. 





Boxline Box owner Mike Evans talking on the return channel behind the scenes at the daVinci booth, one of 3 locations we used at the AUA convention and the site of the live 3D broadcast.

 Standing-room only at the first live 3D robotic surgery broadcast. 

Our live 3D broadcast used two matched HD encoders with DCI downlinking the two signals on standard receiver/decoders.  We fed both signals through a two-channel Aja FS2 frame synchronizer which times them together as a reference, but does not do anything to any propagation delay differences.  from there, both signals went into distribution amplifiers, where one "eye" was broken off and used for 2D-only displays and recording.  We had rented a PrimeImage Pipeline, a piece of equipment  typically used to dial in 10-15 seconds of delay to allow producers to "bleep" objectionable language on a live broadcast.  The delay line is capable of frame-accurate delays, so if one path was even a frame or two ahead of the other, we could "slow" it down to make them match exactly.  Once both "eyes" were exactly lined up, they went into a Aja Hi5-3D, a dual link SDI to HDMI converter, which takes both "eyes" and splits them into a standard HD picture.   This signal is fed to the 3D-capable TV's which when set to the proper 3D mode, stretched the two halves to fill the screen so when viewed with polarized 3D glasses, the image appears 3D.

DCI is happy to work with our friends at Boxline Box on this ground-breaking broadcast.  If you have a special project that needs a dedicated and experienced transmission company, contact DCI.  And if you need to produce a medical-related video, contact Boxline Box! 

A Total DCI Broadcast

One of the things that make DCI unique is being able to supply a complete broadcast solution to our clients.  Typically, the three departments of the company- Teleport, Remote Productions, and Satellite Trucks- operate independently of each other, each with regular clients who use our services to supplement their own capabilities.  Often, two departments will work together- such as a DCI crew using our fiber lines from the White House or Capitol, but its not too often all three get to work together.  When our client needed a complete field production and transmission solution at John Kerry's first speech as Secretary of State, they were able to make one call to DCI for the complete package.

Our Remote Productions department provided three cameras, mics, and lighting for a 2-person interview.  The DCI HD1 satellite truck uplinked all 3 paths to allow the show director to choose the cameras, and also downlinked a network return, all of which went through the DCI Teleport back in Washington.  Using multiplexer and DVB-S2 technology, DCI was able to use roughly half the bandwidth as a typical DVB-S satellite truck with single channel carriers, and still deliver a higher-quality video signal.  Since this client does not own full-time satellite space leases, using half the bandwidth resulted in a visible cost savings. As highly experienced satellite engineers, we are able to suggest new ways of doing transmissions to save our clients money. 

This was a complete DCI production that showcased how all three departments of our company can work together to bring great value and convenience to our clients.  Contact DCI to find out more about our remote production and satellite services. 

Buenos Aires Pope Party

When Argentinian archbishop Jorge Mario Bergoglio of Buenos Aires was elected the new leader of the Catholic church, there was lots of interest in covering the story from Rome.  However, as the first pope from the Americas, many broadcasters also wanted to find out more about Pope Fransisco's background in his hometown of Buenos Aires.  DCI's flyaway, fresh off a quick 3 day trip to Caracas, immediately deployed to the capitol city of Argentina.

Buenos Aires is the second largest city in South America, and many of its residents- including the new pope- trace their ancestors back to Italy.  And just like in Italy, restaurants don't open for dinner until 8:00pm, and its not uncommon for people to be there well after midnight, enjoying the large steaks Argentina is famous for.  Buenos Aires also has a large number of Italian restaurants and pizza shops. 

Our setup was right on the sidewalk around Plaza de Mayo, the large square in front of the "Rose House", the Argentinean presidential residence and other government buildings.

 Across the street was the new pope's old church, and the backgroup of our shot. We took over from a local Ku uplink truck which had a previously-booked job to go cover.  Using a small SUV as an equipment shelter and 5500 watt portable generator for power, we started doing our live shots.

Since this setup was on a public street, not a secured area like our previous job in Caracas, that meant having to break down and setup the antenna and live position every day of the event, a process that took about 45 minutes each time.  The antenna breaks down into six segments for shipping, although we were able to take the entire assembled reflector off the tripod and put it into the back of our SUV, along with the rather heavy generator, and go park it in our hotel's garage.

There was some time one day to visit the neighborhood of Palermo and visit the Recoleta cemetery and its hundreds of ornate mausoleums.

The event cumulated with a live broadcast on four large screens in Plaza de Mayo of Bergoglio being installed as pope, around 5AM local time, however people gathered from about 9PM to watch a series of live concerts and music.

A few hours after the Plaza de Mayo event, the uplink was back on a plane heading home.



Quick in and out events are a hallmark of an airline checkable uplink.  Contact DCI to see how economical this small and powerful flyaway system really is. 

3 Days in Venezuela

When Venezuelan president-for-life Hugo Chavez died, DCI's airline checkable flyaway was the perfect solution to provide 3 paths of transmission to cover the event.  As mentioned in a previous blog post, having an airline checkable flyaway greatly reduces our response time.  We can deploy faster to breaking news situations and still provide the redundancy and high bandwidth transmission networks expect from larger flyaway systems.

New on this job was DCI's newest equipment acquisition, a linear 210 watt traveling wave tube amplifier.  There will be a blog post about this technology in the future, but in short this is the perfection of the TWT amplifier, a technology that has been around for decades.  It is smaller, lighter, and more efficient than our existing flyaway amplifier with similar performance.

  The next day after getting the call the system was ready to transmit from the Intercontinental Hotel in Caracas, where several live shot positions were already setup with a local C-band dish. 

We did a quick site survey at the funeral location, near a military compound, looking for a rooftop position.  Even though it was the day before the funeral, the area was mobbed with Chavistas, most of whom dislike the foreign media.  The Chavistas have a reputation among the 45% of the country who oppose them to be bullies and thugs, and in a city with 3844 murders in 2012 (compared to 414 in larger New York), they are part of the reason Caracas is one of the most violent cities in the world.  People in Caracas live behind bars in the own homes, even windows and balconies ten stories up are covered, while the outside of the buildings look like fortresses with 12' walls topped with high voltage fences.

Building owners and landlords are a group of people the socialist Chavistas disapprove of, and none of them wanted to be seen working with the foreign media, even though we offered them good money for access.  The only other option was to setup right on the sidewalk, but without reliable phone lines for communication and the uncertain security situation of doing live TV  in the middle of the Chaves crowd , we decided to give up on that idea and continue live shots at the secure hotel location.  While not offering the gritty "on site" backdrop of the funeral crowd, the hotel did have dramatic views of the mountains running through the capitol district.


We transmitted a 3 path mux signal in 9MHz on the SatMex 5 satellite, as well as used our receiver on a the local C band dish to downlink the pool feed of the funeral for recording.  After 14 hours of live shots, we packed up and headed to the airport the next morning.



While this was the quickest, busiest flyaway job we have done, it was a great demonstration of the versatility and capability of this unique uplink.  Contact DCI to find our more about our satellite solutions.