A recent report compared streamed image quality to Blu-ray, as it was tested by several viewers with different abilities. The report provided some interesting points. I few months ago I drafted my own research on the subject but I postponed the publishing of the article because other articles required prompt attention. I still plan to publish the article, hopefully soon.
The matter of comparing streaming vs. pre-recorded media in terms of quality, convenience, features, etc. has appeared on the press many times. A common denominator in most cases is that usually the whole picture is not analyzed.
Articles mainly respond to the agenda and format of preference of the writer. Something like: “Netflix has grown by millions of streaming subscribers, and DVD sales are down, therefore pre-recorded media (including Blu-ray) is consequently dead”.
A Distant Matter
Regarding the report/test mentioned above, I agree with the main idea that streamed content may look good enough for many, considering that most viewers have small screens and/or view the content from much further away than 3 times screen height.
That distance is a commonly accepted distance to appreciate HD image quality without seeing the individual pixels and to be able to maintain a wide lateral angle of view (higher than 30%) for the peripheral vision to be engaged so a viewer can be immersed into a movie plot, rather than the feeling of viewing a TV at the end of a tunnel or being on the last row of a movie theater.
How much a viewer can appreciate the differences in image quality of various sources when viewing them on a small screen from 10-15 feet away rather than 5-6 feet away? This is similar to the choice of a 720p panel to a person that insists on a 1080p version when planning to view it from very far away.
The Whole Package or Just the Click
I also agree that most viewers may appreciate more the convenience of streaming than the finer detail on the image, but there are many other trade-offs compared to Blu-ray, such as subtitles and sound in various languages, the streaming aspect-ratio in some cases does not respect the original, bonus materials, chapter access, loss-less audio (many times streaming is just stereo at very low rate), streaming services mostly offer a more limited selection of relatively old content rather than new releases, 2-5Mbps streaming speed rather than 30+Mbps transfer rate both at MPEG-4, to mention a few.
There are people for every market, and the market that considers secondary (or is unable to appreciate) image/audio quality is unfortunately the majority, certainly larger than a typical reader of this magazine would like it to be.
In addition, there is a growing concept of conveniently viewing any content anywhere in portable and small devices. Streaming service providers consider all those factors for their business models and tailor the service to those, and to the majority of viewers.
However, it may soon happen that the pipe service (ISP) over which the streamed content is delivered, a part of the system that Netflix and the like cannot control as they control disc mailing cost/handling, may eventually make the streaming model less economical than traditional linear services if an overwhelming volume of streaming is demanded by an increasingly higher number of subscribers and it becomes an issue to the infrastructure/plans of the pipe provider, regardless how little Netflix or streaming competitors would charge for the content/service.
The 720p claim
Regarding the point that 720p is preferred because it uses less bandwidth than 1080p. When comparing video formats it is important to be clear about which frame rate of the format standard is used in the comparison.
The 720p60fps format, a frame rate preferred by some HDTV content providers such as ESPN, requires less bandwidth than 1080i, but actually requires more bandwidth than 1080p at 24fps, generally used for film sources recorded and delivered at 24fps as the original content is.
Of the following four formats the first 3 are part of the DTV standard (18 formats of the ATSC Table 3):
720p/60fps = 720x1280 = 921,600 x 60 fps = 55,296,000 pixels x sec
1080i/60 = 1080x1920 = 2,073,600 x 30 fps (60 interlaced fields of 540) = 62,208,000 pixels x sec
1080p/24fps = 1080x1920 = 2,073,600 x 24fps (progressive for film sources) = 49,766,400 pixels x sec
1080p/60fps = 1080x1920 = 2,073,600 x 60fps (upconv. from Blu-ray players) = 124,416,000 pixels x sec
There is no need for 1080p to be stored in a disc at 60fps when the original content is 1080p/24fps if sourced from film content, or 1080i/60 (30fps) if sourced from video cameras.
If a higher frame rate or resolution is desired for viewing, the up-conversion could be done at the display point, rather than transporting or storing additional millions of pixels invented by a video processor, that work can be done at the receiving end of the system for the same effect on the image. There is no need for distributing 1080p60fps from content providers that already struggle with pipe usage maximization.
However, it may be beneficial for a source device such a Blu-ray player to de-interlace a 1080i signal when connected to a display device that accepts 1080p60fps “if the player does a better job than the TV on de-interlacing to progressive”. The difference: the transport pipe to deliver such higher bandwidth format is within the viewer’s home: HDMI.
In summary, the standard DTV format of 720p actually requires 12% more bandwidth than 1080p from film sources (55M vs. 49M per sec) due to the higher frame rate of 720p (60 rather than 24 fps), a format that is typically used for ESPN sports content that gets the benefit of faster video frame rates to avoid the interlacing artifacts of 1080i.
In addition, progressive formats are known to be more efficient when applying compression than interlaced formats such as 1080i. Compression (and the overuse of it) plays an important role in the final image quality even when using the more efficient MPEG-4, so those that claim that streaming at 2Mbps provides a similar image than the 30+Mbps Blu-ray version may be missing something in the comparison, perhaps new glasses, although there is a company that I talked to that claimed their compression algorithm was very efficient rendering Blu-ray quality on a near future service with very low rates of transmission, which I would like to cover on a near future article.
Another issue is that some streaming boxes, such as Roku, may receive 1080i content from video sources, but it is downgraded to 720p by the box. The 1920 horizontal pixels of the original 1080i image are downscaled to just the 1280 pixels of the 720p format, losing 33% of spatial resolution on every video frame. The same loss happens if the conversion of 1080i original video content is made at the head-end of the provider to 720p to save bandwidth to distribute it. Those original pixels of resolution are lost and can never be replaced by newly interpolated pixels on a 1080p HDTV with internal video processing.
Ideally, for a streaming device to be flexible enough in the pursuit of quality it should pass-thru 720p, 1080i, or 1080p/24fps content as it is streamed, but should also offer functionality to convert the incoming formats as needed to be compatible to a connected HDTV, even upscaling/de-interlacing to 1080p60fps such as Blu-ray players do. However, the above video-processing capability/functionality does not fit within a model of low cost streaming boxes for a market that prefers convenience over quality and does not know if they are watching HD on their new HDTV.
Good for Plan-B?
So, would the image quality of streaming vs. Blu-ray be similar when viewed on a large screen at appropriate viewing distance? Absolutely not, but it is an acceptable plan-B if for example you are missing some episodes of “24” and do not want to wait for a mailed disc or visit Redbox for an old movie.
During my tests I conveniently watched several early seasons of the series, about 100 one hour episodes viewed back-to-back in a few weeks with no advertisement as the icing-on-the-cake. Quality? Not on a 130+ inches screen even when upscaling to 1080p with my projector. But for plan-B it was OK.
What was the primary goal of that particular plan-B? The content and the convenience, indeed, and to that objective I tolerated image blurriness, softness, pixelization, macro-blocking, etc.
Streaming is also practical if you quickly want to click around to preview some movies in a few minutes before actually streaming the complete version of the final choice, or before committing to a disc for rental/purchase if the image and sound quality you require must be Blu-ray quality. Not to mention if you are a collector.
Posted by Rodolfo La Maestra, June 20, 2011 7:17 AM
About Rodolfo La Maestra
Rodolfo La Maestra is the Senior Technical Director of UHDTV Magazine and HDTV Magazine and participated in the HDTV vision since the late 1980's. In the late 1990's, he began tracking and reviewing HDTV consumer equipment, and authored the annual HDTV Technology Review report, tutorials, and educative articles for HDTV Magazine, DVDetc and HDTVetc magazines, Veritas et Visus Newsletter, Display Search, and served as technical consultant/editor for the "Reference Guide" and the "HDTV Glossary of Terms" for HDTVetc and HDTV Magazines. In 2004, he began recording a weekly HDTV technology program for MD Cable television, which by 2006 reached the rating of second most viewed.
Rodolfo's background encompasses Electronic Engineering, Computer Science, and Audio and Video Electronics, with over 4,700 hours of professional training, a BS in Computer and Information Systems, and thirty+ professional and post-graduate certifications, some from MIT, American, and George Washington Universities. Rodolfo was also Computer Science professor in five institutions between 1966-1973 in Argentina, regarding IBM, Burroughs, and Honeywell mainframe computers. After 38 years of computer systems career, Rodolfo retired in 2003 as Chief of Systems Development from the Inter-American Development Bank directing sixty+ software-development computer professionals, supporting member countries in north/central/south America.