With billions of investment dollars going towards serving up premium 4K content, service providers and content owners must ensure that 4K viewing experiences are truly superior.
This requires a careful, comprehensive approach to 4K content preparation and delivery that requires capable video processing and measurement platforms, as well as the knowledge to properly configure these tools for optimal results.
To assist service providers and content owners, Amazon Web Services’ Elemental released an eight-page White Paper that offers what it says are the five most common pitfalls of 4K video quality impairments.
Elemental also suggests best practices to mitigate or eliminate these issues, thus ensuring the highest quality 4K viewing experience.
PITFALL ONE: RULES AND THRESHOLDS FOR HD CONTENT NO LONGER APPLY
With 4K video, there is “no place to hide” visual defects. Any impairment will be much more prevalent in 4K video simply because of the much higher bitrate, greater number of pixels, and larger viewing surface as compared to HD video. 4K content is more likely, at least initially, to be high motion, high frame rate sports content. Not only is this content complicated to properly encode, but the higher frame rate further magnifies the frequency with which errors occur in a 4K vs. HD viewing experience.
Best Practice: Quality levels must be higher for 4K video to offer a viewing experience equivalent to what users are accustomed to with HD. Establish settings and monitoring thresholds tailored for 4K content.
PITFALL TWO: OVER-COMPRESSION
4K video requires greater processing capacity and greater bandwidth than HD to create a satisfactory viewing experience. Squeezing video resources to maximize video processing and network capacity over existing network resources can create highly visible defects. This may be mitigated by shifting to more efficient codecs, such as HEVC, but may only provide partial benefits when delivering high motion, high frame rate 4K content.
Best Practice: Properly design and scale network capacity to deliver crisp and life-like 4K video experiences, especially for high motion sports content.
PITFALL THREE: EXCESSIVELY VARIABLE PACKET AND BITRATE OUTPUT
For all video content, there is a high degree of variability in encoding complexity and processor utilization from one frame to the next, especially at scene changes. This is also true for 4K content, especially at higher frame rates such as 100fps or 120fps. Encoding more complex frames can result in bursts of output traffic, while encoding less complex frames causes decreased output traffic.
Best Practice: Monitor the maximum peak variable bitrate (VBR) of traffic from the encoder, with notification for significant and fluctuating bursts. With specific network capabilities in mind, operators must balance VBR settings (both maximum and minimum) in the encoder, though this may impact 4K video quality especially at high frame rates. Operators can also choose a statistical multiplexer to more efficiently use available network capacity during real-time fluctuations.
PITFALL FOUR: VARYING QUALITY OF ADAPTIVE BITRATE OUTPUT STREAMS
Adaptive bitrate (ABR) streaming has become increasingly popular for delivering video content to multiscreen devices, particularly over unmanaged or third party networks for over-the-top (OTT) delivery. This allows client devices to request, on the fly, higher or lower resolutions and bitrates in response to changing network conditions to ensure faster video playback starts and an uninterrupted video flow.
Best Practice: Monitoring the quality of each stream and GOP alignment is important to detect errors or problems with individual ABR output profiles and will eliminate visible video playback stutters.
PITFALL FIVE: GOP MISALIGNMENT ACROSS ABR OUTPUT STREAMS
4K encoding is processor and resource intensive. Even with the most robust 4K encoders, the number of output streams that the encoder is physically able to encode is far more limited than the number of HD or SD streams that the same encoder could generate. To produce a complete, high-quality ABR bouquet – for example, two 4K profiles, two 1080p profiles, two 720p profiles, and two to four SD profiles – an operator may typically split the encoding across two devices to manage processor load. In this example, each encoder would produce one each of the 4K, 1080p, 720p output streams, and one or two of the SD profiles. This more evenly distributes the processor workload and provides redundancy. If one of the encoders fails, the operator is still able to deliver at least one output stream in each resolution. However, dividing the encoding workload may potentially introduce mismatched output timing.
As Elemental notes, 4K video is in a period of refinement, where companies across the video ecosystem have the opportunity to optimize the viewing experience for customers.
Because of the higher resolution of 4K video, physically larger viewing space, and higher frame rates, consumers are more likely to perceive visual defects in 4K playback. To provide the most seamless experience for viewers, operators must understand optimal encoder settings and recognize the unique settings that each network configuration requires for encoding, packaging, and delivery.