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Monitoring Compressed Media: Tools for Analyzing Signal and Stream Integrity

To meet demand, technology suppliers have leveraged ongoing advances in digital processing to incorporate more powerful and sophisticated video and audio processing.

IT- and IP-based technologies have become a part of most modern media facilities. The resulting ubiquity of hybrid SDI/IP infrastructure demands that broadcasters be able to monitor both SDI signals and MPEG streams—not only as signals move between components internally, but also as they are accepted from or distributed to external sources and partners.

To meet this demand, technology suppliers have leveraged the ongoing advances in digital processing to incorporate more powerful and sophisticated video and audio processing into new universal confidence monitoring systems. The modern confidence monitor unites support for both baseband signals and MPEG transport streams with stream-specific analysis. The baseband input of the universal confidence monitor allows it to accept signals from SD-SDI up to 3G HD-SDI 1080p60 with full 4:2:2 support, and the monitor’s built-in decoder allows it to support broadcast standards including DVB, ATSC and ISDB, with video encoded as MPEG-2 and MPEG-4 4:2:0. Smoothly handling virtually any type of input or output, this type of monitor can significantly boost the efficiency and agility with which users can validate signal and stream integrity—and ultimately the quality of their services.

By simplifying and accelerating the decoding of MPEG input sources and analysis of the transport stream wrapper, such universal confidence monitors offer a convenient solution for identifying errors that might impair decoding, cause artifacts in the decoded picture, or prevent decoding entirely. Users can look at elementary stream components such as video, audio and data PIDs to ensure that audio and video are being encoded correctly. On-screen level meters allow users to watch up to 16 channels of audio, and built-in speakers and a headphone jack typically are included in the system to let the user listen more carefully to selected audio tracks.

When equipped with a set of analysis tools, the universal confidence monitor supports close scrutiny of the transport stream and its components. Along with information including the program number, PMT number and service description, each stream component is displayed along with bit rate, which aids the user in confirming that data table references relate to actual data. By comparing stream inputs with a subset of the ETR101290 standard, the monitor can automatically generate alarms that inform the user if tables are late, have not arrived at all, have arrived but are out of specification, or have arrived and are within specification.

Figure 2. Monitoring in the multiplex stage

The universal confidence monitor is most often deployed in contribution and distribution signal flows for the basic but important task of monitoring a single-channel-encoder. (See figure 1.)

In this straightforward monitoring scenario, the universal confidence monitor accepts the same uncompressed SDI signal (from playout) being sent to the encoder, as well as the compressed MPEG output of the encoder. With two or more integrated display screens, the monitoring unit allows the user to examine, side by side, details about both inputs to ensure that audio, video and data were compressed properly.

The universal confidence monitor also plays a valuable role in more complex scenarios, such as that shown in figure 2.

When uncompressed streams from various sources are fed into an encoder, output as individual MPEG streams, and then fed together into a multiplexer to create a multi-program transport stream, several universal confidence monitors can be deployed strategically to provide full visibility into all signals and streams at all times. Users can thereby keep a close eye on the integrity of audio, video and data throughout the encoding and multiplexing processes.

Figure 3. Comparison of two program stream multiplexes

As the diagram in figure 2 illustrates, one multiscreen confidence monitor may be placed upstream of the encoder and another downstream of the encoder to provide a “before and after” look at compressed content. With a dual-screen monitor at the tail end of the multiplexing process, the user also can examine the multiplexed program stream output.

Finally, when the monitoring scenario calls for comparison of two program stream multiplexes, as is often the case for monitoring of main and backup streams, a dual-screen universal confidence monitor simplifies the comparison of transport streams. This model is shown in figure 3, with a dual-screen unit accepting inputs from the A and B chain and displaying table data for each stream multiplex. As in any other area of operation, the monitor’s MPEG analysis toolset allows the user to drill down into this data to identify any potential issues.

The increasing complexity of the broadcast environment presents a new host of potential points of error, particularly as broadcasters deliver more content to a greater number and variety of outlets. For this reason, it is critical that operators establish an efficient means of managing and monitoring signals across the delivery chain. Uniting MPEG-4/H.264 stream monitoring with baseband monitoring, today’s universal confidence monitors offer a convenient and cost-effective solution for comprehensive monitoring.

Graham Taylor is MPEG product manager at Wohler Technologies.

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