Test, QC & Monitoring Global Viewpoint – September 2016
QC And Monitoring Requirements for Live and VOD OTT Workflows
A file-based QC and monitor solution helps ensure that broadcasters deliver high quality video and audio, which helps retain viewers.
Given viewers' changing demands, broadcasters need to embrace OTT workflows. Yet, ensuring accurate delivery of technically sound content is challenging and requires the proper set of reliable QC and monitoring tools. Here are some suggested practices.
OTT and video streaming consumption have increased significantly in recent years. In the U.S., 86 percent of smartphone users watch video content on their phones, according to a recent report from Ericsson. Given the changing viewing demands, broadcasters need to embrace OTT workflows. Yet, ensuring accurate delivery of technically sound content is challenging. Broadcasters require a reliable set of quality control (QC) and monitoring tools to stay competitive in the OTT environment. This article outlines the key capabilities for QC and monitoring tools in the OTT environment, with a focus on both live and VOD workflows.
OTT Workflow for VOD vs. Live Streams
In the broadcast realm, stored programs (i.e., VOD assets) are managed via file-based workflows. In this case, broadcasters have the time and luxury to guarantee that all assets are of superior quality by using file-based QC tools during the content preparation stage. However, in the case of live streams, content is transcoded in real time into various ABR formats. In both the cases, any delivery issues with real-time streaming are verified using real-time OTT content monitoring tools.
QC and Monitoring for VOD Assets in OTT Workflow
To be able to effectively monetize OTT VOD content, broadcasters need a unified QC and monitoring solution, as shown in Figure 1. It’s important that they choose a solution that supports both content preparation as well as content distribution. This will ensure the best possible experience for viewers.
QC During Content Preparation
During the content preparation phase, broadcasters need to confirm that the quality of the original content is good. File-based QC solutions can be used to address quality problems ranging from ingest to editing, compression artifacts introduced during transcoding, as well as file assembly issues.
Common QC checks include baseband quality, compression artifacts, file integrity, and standards compliance. For baseband quality checks, it is essential that content is checked according to various quality parameters before final delivery. A comprehensive QC tool needs to be used for a wide range of baseband quality checks, such as video signal levels, color bleeding, blotches, blur, defective pixels, black frames, color bars, RGB color gamut, mosquito noise, audio levels, audio noise, etc. A good QC tool will make sure that these issues are detected with a very high level of accuracy and reliability, with minimal false positives.
When the content is compressed, several artifacts like blockiness, pixilation, Moiré pattern, and ringing artifacts may be introduced in the video. Broadcasters will want to look for a QC tool that keeps transcoded content artifact-free.
File integrity and compliance checks ensure that the file or content being delivered is not corrupt and has been encoded as per industry standards. If these requirements are not met, downstream tools may not be able to play out the assets accurately. This is especially important in the OTT environment, where there are a host of devices with different form factors and players from a multitude of vendors. Content must play well on all of those devices.
Multi-Segment ABR Transcoding
Once master/mezzanine content has been verified using a file-based QC solution, it moves onto ABRtranscoding. ABR transcoding is a complex process involving the creation of multiple renditions of the same content at different quality levels and bitrates. The transcoding process is not only time-consuming but also requires proper alignment between different variants and correct segmentation of each variant. Failure to achieve that can result in playback issues, leading to revenue loss. Different file-based QC and monitoring systems can be used to check for ABR specific issues and send an alarm to broadcasters before the ABR package goes out for delivery.
OTT delivery leverages ABR technology. ABR requires content to be split into short segments of typically 10 seconds each. This ensures seamless and fast switching between different variants. Typically, each ABR package is encoded at multiple bitrates. When the content is played, the streamed content switches between bitrates as it moves to the next chunk, managed using the manifest file and depending on the network congestion and other factors influencing delivery quality.
When content is transcoded for ABR playback, several additional checks need to be performed on the transcoded content before the content is ABR ready. One example is checking thateach segment starts with an independent frame. By making sure that no chunk has decoding dependency on the previous one, a seamless switch can happen during playback when moving from one chunk to another.
Broadcasters will also want to check that all variants of the content are properly aligned in terms of number of segments, segment duration, total duration, and content structure. A client can choose to play backa particular variant depending on the download bandwidth available and device screen size; therefore, it is imperative that all the variants are consistent with each other and allow seamless switching across all of the available variants.
Another important check is consistency between metadata and actual content properties. A client uses the metadata in the manifest files to choose the best playback quality. If there is any inconsistency between the metadata and the actual media properties, it may lead to playback issues and a bad user experience.
Once the content is validated from these checks, it is ready for delivery across linear and OTT workflows. The content is encrypted with one or more DRM technologies before it is moved to the origin server for OTT delivery.
Ideally, the file-based QC solution should have the capability to perform all of the above ABR checks as well as a deep analysis to identify any baseband issues. Once the content moves to the distribution stage, the focus shifts to confirming smooth content delivery and the best possible user experience. During this phase, broadcasters will need to deploy state-of-the-art monitoring solutions.
Monitoring VOD Assets During Content Distribution
Monitoring VOD assets during distribution involves real-time streaming validations. There is some overlap with the file-based QC done throughout the content preparation stage. This is necessary to ensure content stability as it is replicated from the origin server to cache/replica servers in a typical distribution or Content Distribution Network (CDN) environment. However, the accuracy and details of file-based QC are not needed at this stage. Limited QC is sufficient and significantly faster.
There are a few important criteria for monitoring tools at this stage. The content manifest should be accessible over HTTP/HTTPS. In addition, all the references to profile manifests and individual segments should be available. Content must be properly conditioned for ABR, and the server needs the capability to respond fast enough so that content is downloaded within acceptable delay and buffering parameters; otherwise the playback experience may be majorly impacted.
Content downloads can be simulated in a network congestion environment to observe how the distribution server behaves under stressful conditions.
Broadcasters may also want to decrypt content at this stage to ensure that no issues were introduced during encryption. Basic audio-video quality checks (e.g., blockiness, black frame, audio loudness, etc.) will need to be done. It’s recommended that broadcasters set up passive monitoring of all the requests and responses for clients accessing the content. Furthermore, all HTTP response codes should be monitored and logged.
ABR Transcoding and Monitoring for OTT Live Streams
The typical live stream workflow for OTT deliveries is shown in Figure 2 above. The live stream is split into segments, and as segments are received, they are transcoded in real-time to the desired ABR format. After the segments are encrypted with DRM technologies, they’re placed on the origin servers for real-time consumption. As more segments are added, the older ones get removed. The process continues through the duration of the live content.
A full file-based QC solution isn’t required; however, broadcasters still need to ensure that basic baseband checks are done, ABR transcoding is happening properly, and the timing and loading of segments to the servers are well managed to maintain high QoS and QoE. These checks can be done easily using content monitoring tools, similar to the workflow for VOD assets.
OTT technology is still evolving, and the requirements for monitoring are also changing. Monitoring tools need to be architecturally versatile in order to accommodate this environment and allow broadcasters to figure out which issues are the most critical ones to focus on.
Ultimately, broadcasters should choose an OTT monitoring solution for live and VOD assets that works in tandem with a file-based QC tool. (See Figure 3 above.) By deploying a complete QC and monitoring solution for ingest to delivery, broadcasters can deliver the best QoS and QoE to viewers in the OTT world.