Multifeed contribution context
Sports television program providers know well that the duration of a soccer game is not always 90 minutes, and the game may go into overtime. Tennis finals can be delayed because of rain, and a golf tournament could last longer than expected. In this situation, a new channel may need to be added in the multiplex while other programs are unexpectedly overlapping the scheduled transmission slot. Hence, the sports feed distributor could face a peak of usage in its multiplexes because the line-up of feeds to deliver becomes too important at the time. Live feed turn-around operations are often subject to immediate changes, but it is unlikely that world feed distributors will get in touch with satellite or fiber service providers to instantly adapt the bandwidth capacity. Therefore, an extra bandwidth capacity margin will be rented and saved to be used “just in case.”
On the technical side, in a typical contribution multiplex, multiple-program transport stream (MPTS), each program bit rate needs to be taken into account when booking or planning the transport bandwidth capacity. This capacity will depend on the number of programs to turn around, including their specifications, such as the video format, the number of audio channels, the type of audio and the targeted video quality. Therefore, optimizing the use of the bandwidth in the multiplex can become complex.
The challenge: Avoiding service disruption when applying changes
As the program line-up could vary, the operator needs to free some bandwidth in the broadcasted multiplex to add a new channel in it. Moreover, this needs to be done without affecting the current services on-air. Contribution content distributors, such as Eurovision, from time to time, need to adjust the video bit rate of each video encoder in the same multiplexed MPTS.
Contribution video encoders configured in classic CBR need to stop and restart to produce a new MPEG-2 transport stream with a new video bit rate. This induces a stream discontinuity and therefore a “black” screen. Even if this “pause” is generally short at the encoder level, any MPEG-2 transport stream disruption will cause a disruption at the decoder level, or should we say, at the viewer level.
Considering that the new channel added in the multiplex line-up has to start at a time that may not be convenient for the other channels to be interrupted, this could lead to stressful situations for the operators.
In order to fit one or more channels in the multiplexed MPTS, the video bit rate of each current encoder needs to be reduced. The MPTS needs to remain continuous, without disruption, even if a program is added or removed. Adding or removing a program in the multiplex should not impact the continuity of the other programs.
SIDEBAR: Eurovision's use of Seamless Channel Insertion
Eurovision is a distributor of sports and news content for the world’s broadcast and media platforms. As such, Eurovision faced the issue of its television program line-up changing regularly.
“The content broadcasted is very versatile, especially in terms of duration on-the-air,” says Eurovision special project director, Puiu Dolea. “The distributed services line-up can be reshaped several times within the same day. We needed more flexibility from our encoding platform.”
ATEME has implemented SCI rate control in its Kyrion line of contribution encoders at the request of Eurovision, allowing operators to change video bit rates on the fly with no service interruption. The streams delivered to EBU members and affiliates are still constant bit rate, but their bit rates can now be changed without affecting the consistency of the entire turn-around multiplex. There was no impact, no change of firmware or disruption on the receiver side following the implementation.