Why End-to-End QoS and QoE Multiscreen Monitoring Is Essential
Broadcast TV has set a high bar for viewer expectations and delivering a great quality of experience. As the trend and demand for multiscreen viewing and TV Everywhere continues to grow so does the demand for a high quality experience regardless of the device being used. Behind that multiscreen experience lies some complex adaptive bit rate (ABR) technology and a new set of monitoring challenges.
To give content providers visibility into their content and let them rapidly identify and address issues that impact user experience requires a sophisticated set of monitoring and analysis tools. Those tools need to provide comprehensive insights into both the quality of experience (QoE) and quality of service (QoS) on the delivery network being employed. These systems need to check everything from validating the availability of the assets to determining the quality of those assets even if they are encrypted.
ABR provides a mechanism for real-time and continuous display of video no matter how much or how little bandwidth is available on the device being used. It does this by fragmenting or packaging the content into small 2- to 10-second segments with several profiles (the same content at different bit rates) and then delivering the correct sequence of fragments at a bit rate that suits the available bandwidth. This means that to deliver a constant stream of content that does not falter the quality of the video will vary according to bit rate and available bandwidth. To be sure, the higher the bit rate the better the quality of experience, but most importantly as long as some bandwidth is available the video will keep playing.
Any ABR system works by actively measuring the latency, available bandwidth, and how full the playout device buffer is. If it is becoming full, the client device requests a lower bitrate profile. As the buffer empties the device requests a higher bitrate profile.
Figure 1 illustrates the key principles behind this. In this particular example the segments are occurring on 2 second boundaries and it shows the seamless transition of the content on a device as it moves between different profiles. The same thing could happen on a single device as it moves between different networks and the overall available bandwidth varies, such as when switching between a Wi-Fi network and a cell phone network.
Note that it is vital that the switch over boundaries, normally called encoder boundary points (EBPs), are perfectly aligned. If they are not there will be discontinuities in the displayed video when the device switches between profiles.
One of the biggest challenges of content streaming is that the networks and devices are far more varied and non-deterministic than those found in the more controlled environments of cable, satellite, terrestrial, and IPTV. Different network conditions and device requirements make such a highly adaptable architecture necessary in order to maintain uninterrupted content delivery.
With ABR increasingly going mainstream and now also being used to deliver linear content, service providers must not only ensure that transcoders create the appropriate profiles, but also that video can be monitored from acquisition (e.g., satellite, fiber, file) all the way to the origin server and content delivery network (CDN) servers.
Why Monitor?
For service providers to ensure they are delivering, or are going to deliver, a great experience to their customers a number of essential checks need to be made. Is the quality of the delivered content prior to being processed for streaming good? Is the asset to be streamed and all its profiles available to be streamed if requested? If it is played out, are the asset and its profiles structured correctly to ensure seamless and problem-free playback?
Answering these questions requires a set of tools to assist in the QC, monitoring and testing of assets each step along the way. These range from real-time monitors capable of scaling to look at multiple programs simultaneously, file-based QC tools to look at stored content, and monitors that can actively subscribe to an ABR service to ensure availability and quality of the content.
What to Look at and Where
At the heart of any ABR system is the packagers. The packager performs three main functions. It transcodes the input content into multiple bitrates (on many systems there can be eight different bitrate profiles produced). The packager will then fragment these profiles into 2- to 10-second segments, and then finally (in many, but not all cases) it will encrypt the fragmented profiles before delivery to the origin servers or CDN.
Streams or content that arrives at the input to the packager have been initially monitored through the distribution network to the ingest point. This could be live content being received or episodic content being played from servers elsewhere in the network. It is important that the ingested content is error-free when received by the service provider. If there are flaws in the ingested video and audio, it is inevitable that the final service will not be acceptable.
There is a lot of content to be monitored at this point and any deployed solution needs to be able to scale to handle the volume and actually look at the content for QoE issues such as macroblocking, compression artefacts, audio silence, audio levels, and loudness. Similar tests may also need to be performed on episodic content using file-based QC tools on servers where the content is stored.
Once the content has been packaged and delivered to the CDN, the only way to ensure that the content or assets will be available on request is to use probes or devices that can actively subscribe to the service. By doing this the probe can check the manifest for the asset and ensure that the various profiles are available for playout along with performing tests to check segment load and latency times. In addition to this, probes can check the EBPs for alignment to ensure seamless switching between profiles. The amount of content subscribed to by probes can be easily managed to minimize the load on origin servers or the CDN.
In situations where the content has been encrypted, basic probes can only provide QoS measurements. There are more advanced probes available that, with the cooperation of the service providers, allow the content to be decrypted and QoE measurements performed. This lets the service provider know that not only is the content available for delivery, but also when it is delivered it will be good quality. QoE measurements that require decryption tend to be easier to handle inside a managed network. In unmanaged networks, probes are required to interface with the DRM suppliers to gain access to the content.
Summary
With ABR streaming services, it is important to use a combination of QoS and QoE monitoring from ingest, through transcode, fragmentation, and encryption for all available profiles. It is critical to establish and test the content at the beginning of the chain to ensure what is going into the system is a known good entity. On the delivery side, providers need to test that the content will be available when requested and that it will play successfully. In short, it is about ensuring that what goes in is great and what comes out leads to the best possible experience for the customer.
[Ian Valentine is the business director for video products at Tektronix. StreamingMedia.com accepts vendor-contributed articles like this one based solely on their value to our readers.]
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