Safeguarding Video Resolution

Despite many advances in video technology, the rush to adopt convenient distribution mechanisms has denied consumers the most realistic and immersive experience, both in the theater and at home. Theaters survived the expensive transition to 2K digital cinema with Hollywood’s assistance, but many have remained there and not made the leap to 4K. Home cinema began to optimize for Blu-ray video and audio formats, but as discs have declined in sales, so too has the quest for quality; consumers have adapted their equipment to the signals of streaming services, so now a mid-range TV and sound bar may be seen as a perfectly adequate home cinema. Just as CDs gave way to MP3s, there is a self-fulfilling lowering of A/V quality and user expectations, so that now it is only the luxury home cinema owner, playing high-quality content, who has the chance to appreciate the difference between good and great audio and video. Most consumers never realize the full potential of their 4K TV/projector and audio processor due to the intentionally lower quality delivered by streaming services. Kaleidescape remains committed to safeguarding video and audio resolution as it comes from the movie studios and ensuring the best possible home cinema experience.

Video format changes, like the transition to HD and more recently 4K and HDR, are quick to make headlines but slow to be widely adopted. The movie production workflow is extremely complex, and until recently it has been impractical to shoot with only the highest resolution cameras. The maturity of 2K CGI processing (potentially one-quarter the storage and latency of 4K) has made HD quality standard, entrenching HD distribution models, both to 2K projectors in theaters and to streaming services optimized for HD. While 4K and HDR processing has become the new standard, unfortunately environments where viewers can appreciate all this A/V quality are scarce. Theaters with 4K projectors may have the resolution, but few use the latest laser technology, and so they appear dim and washed out compared to home cinema HDR. Consumers at home with bright new 4K TVs often waste their potential on low-bandwidth streaming services that effectively reduce the resolution back to HD. Quality is being dropped through the cracks, leaving the movie lover with only one place to enjoy the craftsmanship of new releases painstakingly mastered using the latest technology – the high-end custom home cinema.

Fortunately, if you know which features to look for, 4K and HDR displays and receivers are not only available but can be affordable. The final piece of enlightenment is an awareness of the “garbage in, garbage out” principle – the equipment is only going to look and sound as good as the source material being played. Kaleidescape Strato players can deliver 5-10 times the bandwidth of streamed video, and 10-50 times the bandwidth of streamed audio – differences that can be evident even on a mid-range TV and soundbar, and undeniable on high-end equipment. A side effect of Dolby promoting its own formats has been their policing of post-production – studio masters now boast exceptional video and audio fidelity, regardless of the final distribution format. In particular, Dolby Atmos and DTS-X object-based audio can be delivered lossless to most audio receivers and processors (using Dolby TrueHD and DTS-HD MA) for a theatrical surround-sound experience.

Why bother with the best quality, when there are “good enough” solutions? The better question is, why throw away the video resolution and lossless audio quality that new displays and receivers were specifically designed to play?

For video, codecs like HEVC (H.265) compress by removing bits from the source video data, so they are cleverly designed to take those bits from places where they are less likely to be noticed: dark regions like shadows, edges, fast-moving objects. Also, since a colorless black-and-white movie contains most of the useful signal and is quite watchable, the codec favors removing color detail (chroma) over removing brightness detail (luma). While HEVC has fewer macroblocking artifacts than its predecessor AVC (H.264), the missing bits are swept under the carpet somewhere, and so it’s good to know what artifacts to watch out for.

If you want to know how much data is being discarded, a low “bitrate” is the smoking gun. A signal with a bitrate of 65-100 Mb/s, as found in Kaleidescape’s movies and on UltraHD Blu-ray discs, is retaining up to ten times as much information as in a 10-20 Mb/s streamed video – although both may be described as “4K”. The differences are tricky to describe in words, but they are visible if you know what to look for.

Gradients, that is, smooth transitions in color or brightness, require many color levels. A bit depth of 8 supports 2^8 = 256 levels, and a bit depth of 10 (required for HDR) supports 2^10 = 1024 levels. When there are not enough levels, there will be banding artifacts. HEVC attempts to hide these artifacts in shadow areas.

Moving from HD to 4K means that one pixel becomes a 2x2 grid of four pixels. For low-bandwidth 4K streaming, if those four pixels all have the same color, there is really no additional information beyond what the HD stream held – scaling the HD stream would give exactly the same appearance on the display. When watching 4K video, the expectation is that the four pixels in each 2x2 grid are unique, revealing detail of texture or edges that go beyond what was available in the HD stream. Low-bandwidth video that fails to add detail in 2x2 or larger groups of pixels will show blockiness. HEVC compression is better at hiding blockiness than AVC was, but it’s still possible to see it in some cases.

Edges of objects can include a lot of high-frequency detail. But since pixel variations along the edge are hard to discern, especially if the edge is moving, HEVC tends to discard information here. Removing edge detail effectively reduces the resolution of the video, as if the camera were slightly out of focus.

Fast-moving or flickering objects can cause sudden changes in bandwidth, as each new frame contains information that can’t be predicted from the previous frame. If a low-resolution approximation of the flickering object is sufficient, according to HEVC’s video quality metrics, detail may be omitted so the number of bits can be minimized. Viewers of streaming services may not have the opportunity to step through the video frame by frame, so approximation errors, even once noticed, can be hard to confirm. While its difficult to illustrate temporal artifacts in a static document, the viewer may see more judder in the video or feel that fast-moving scenes are blurry. The issues are confused by modern displays offering additional video processing that interpolates between frames – the resulting smoothness of the motion (often called the “soap opera effect”) can make video details more apparent, but the interpolation is error-prone and is generally not what the director intended.

Displays are brighter and more colorful than ever, to the point that their color gamuts far exceed what was planned for in older SDR video signals. Viewers with uncalibrated displays can still see bright, vivid colors from an SDR signal, especially when using the excessive processing most displays default to – but these extreme colors are likely not what was observed during mastering on a reference display. 4K HDR technology makes it possible to more accurately specify the color and brightness as found in the studio master, while making fuller use of the display’s wide color gamut and simultaneously providing greater spatial and temporal resolution. For best display performance, use 4K HDR.

Blu-ray audio was a tremendous innovation: up to 8 channels of audio, each with a potential bandwidth several times higher than CD quality. The latest audio standards – object-based audio like Dolby Atmos in a lossless TrueHD signal – combine the highest bandwidth of Blu-ray with the ability to accurately position objects aurally, independent of the number of speakers in use. Streaming services fail to realize the full potential of Dolby Atmos due to bandwidth limitations, but lossless theatrical surround-sound is within reach, if you choose a source device that supports Dolby TrueHD for Atmos, and DTS-HDMA for DTS-X.

It’s increasingly easy to access movies, concerts, and television from a wide variety of streaming sources. Discs, despite their quality advantages, have lost the battle. To the average consumer, it seems that the cost of all this convenience is a reduction in audio and video quality, and a reduction in ease of use. If only it were possible to experience the quality of the best UltraHD Blu-ray discs through a convenient user interface; and to search for, buy, and instantly download any Hollywood studio’s movies from just one source, without leaving the couch. But it is possible: Luxury home cinema without compromise – that’s Kaleidescape.

HDR in commercial theaters:
Digital Cinema Report: DCI Must Do More on HDR

Video compression artifacts:
Biamp: Understanding Video Compression Artifacts