In the digital TV era it becomes significantly important to use and maintain content in the compressed domain and to avoid recompression where possible. Another consideration, especially for multi-channel operations is to reduce the cost per channel by eliminating as many devices on the chain as reasonable.
AirBox Streamer was designed specifically with this task in mind. It’s an all-in-one playout automation, server and DVB encoder in a single unit. It comes configured either with a UDP streaming port or with a DVB/ASI port, ready for DVB transmission.
ASI stands for Asynchronous Serial Interface. It’s bitstream signal is very similar to SDI, but it can contain different kind of data, including but not limited to MPEG2 and H.264 video packets. SDI carries uncompressed video. In fact one can use SDI-compliant cables to interconnect ASI equipment.
Both SD-SDI and ASI share the same bandwidth – 270 Mbit/sec. Some higher grade SDI matrix switchers support ASI signal routing as well – this is specifically mentioned in their specifications.
All professional satellite equipment operates with ASI interface. This means that DVB encoders and multiplexers talk to each other via ASI interface.
A “traditional” DVB transmission looks like this:
- Video sources (such as video servers, VTRs, live cams, etc.) all go into a vision mixer (or matrix switcher) through SDI or analogue video signal;
- In the vision mixer or downstream keyer there might be graphics insertion;
- There can also be logo insertion by a dedicated logo inserter (SDI or analogue);
- The resulting SDI or analogue video signal is then fed into a DVB encoder with ASI outputs (e.g. MPEG2 TS at 3-6 Mbit/sec);
- This ASI signal is then fed into a DVB multiplexer which assigns it a Program ID and includes it into the total bouquet of other DVB programs;
- Its ASI output is then sent to the satellite.With the direct AirBox DVB/ASI playout you can now achieve a different scheme: AirBox DVB/ASI output is directly supplied to a DVB multiplexer, thus avoiding the usage of a costly DVB encoder ($5K – $20K range).
The following considerations need to be made, when discussing this approach:
AirBox has 2 streaming modes named “Pump” and “Stream” respectively. Each of them has its advantages and limitations, depending on the streaming purpose:
– Pump (e.g. IP Pump and ASI Pump AirBox modules) sends to its UDP or DVB/ASI output the original source MPEG2 streams with their original bitrate, so all source files must have the same bitrate (typically 3-6 Mbit/sec), or the bandwidth of the streaming receiver must allow for variable bitrate. If content comes from different providers with (naturally) different bitrates, “transrating” or “bitrate shaping” might be required. Changing the original bitrate by discarding the less significant MPEG2 information or by stuffing the stream with null data is done by the so called “bitrate changers / shapers” or “transraters”. They are either stand-alone devices or this process is integrated into the DVB multiplexer. Specifying a standard content bitrate will alleviate all that hassle of course. The main advantages of this approach are that the original video quality is preserved and multi-channel operation can run on a single server;
– Stream (e.g. IP Stream and ASI Stream AirBox modules) sends to its UDP or DVB/ASI output a recompressed video stream. The main advantages of this approach are that the entire output stream has the same selectable and unified bitrate, any graphics can be inserted (logos, subtitles, TitleBox, etc.), output compression type can be selected (e.g. MPEG2, H.264/AVC or WMV/VC-1).
In both cases live video sources (if required) have to be converted and sent to AirBox as live MPEG2 streams. This is possible by using CaptureBox Streamer (CaptureBox + its streaming option), it converts uncompressed SDI or analogue video sources to live MPEG2 streaming video (UDP) in real-time.
Typical application examples:
- UDP streaming – video-on-demand projects, where the VOD operator needs a multi-channel playout system with a number of MPEG2 streams to be sent over a regular computer network to a number of recipients;
- UDP streaming – feed PlayBox DVB Muxer or a third-party multiplexer;
- UDP streaming – feed remotely located set-top boxes with video;
- Direct ASI output – commercial insertion at satellite uplink operators;
- Direct ASI output – avoid external DVB encoders.