Surprise inspection! How many video sites have you bought as a member? If you love to follow dramas, have you unlocked ultra-clear clarity on every website?
Friends may have noticed, I don't know when it started, several mainstream video websites marked different levels of video clarity under the video.
The video clarity was initially available in three levels: SD, HD and Ultra HD, and later added members-only Blu-ray 1080p and 4K quality.
And these quality levels are often different on major video sites, which is dazzling and unclear.
What is the mystery of video clarity? What is "blue light" again?
Sometimes, even if some videos are turned on Blu-ray, the picture quality is still blurry and the clarity is not satisfactory, what is the matter? Don't worry, this will take you to find out!
The image quality rating of some video sites. Image source: Video website screenshot
I believe that friends are no strangers to the word resolution, it is the decisive factor in the clarity of the video, which indirectly leads many partners to equate the image quality and resolution we often say 720p, 1080p.
In fact, the original expression "digital + p" did not refer to a fixed resolution, but a video display format.
P here refers to the number of vertical pixel lines on the display, and 720p is 720 lines.
Later, this concept was extended to digital cinema standards, which became the relevant definition of video resolution.
Resolution diagram. Image source: Wikipedia
According to the current video industry resolution specification, SD refers to video formats with a physical resolution below 720p with low definition.
And HD has two internationally recognized standards, one is that the vertical resolution of the video is not less than 720p or 1080i, and the other is that the video aspect ratio is 16:9.
HD includes 720p, 1080i, and 1080p, unlike above, where p and i represent progressive and interlaced scans, respectively.
At the same resolution, progressive scan is better than interlaced scanning.
Generally speaking, the resolution of 720p and above can be called a high-definition signal source.
Correspondingly, industry insiders call 720p standard HD, while 1080i and 1080p are called Full HD.
Unlike industry standards, the ultra-clear picture quality displayed on video websites generally refers to 1080p Full HD quality, and HD quality generally refers to 720p.
Seeing this, many friends may ask, what is Blu-ray and 4K?
Blu-ray, also known as Blu-ray disc, full name is Blu-ray Disc, abbreviated as BD, refers to a kind of storage disc.
Because it uses a blue laser with a shorter wavelength to read and write data, we call it "blue light".
But unlike the HD and Ultra HD mentioned above, it does not refer to a certain video clarity specifically.
Blu-ray discs have a large storage capacity, generally dozens of G, so they can store some videos with high bitrate and good picture quality.
4K video refers to video with a resolution of 3840×2060, also known as 2060p. With 4,000 pixels in landscape and a total of more than 8 million pixels, it is one of the highest-resolution digital films available, with high clarity and excellent looks.
Schematic diagram of the effect of different definitions. Image source: Wikipedia
In some video sites, Blu-ray 1080p is often regarded as a higher definition level, which requires membership permission to watch or cache, so what is Blu-ray quality?
What is the difference between Blu-ray on video websites and Blu-ray quality in the true sense?
Generally speaking, the main factors affecting image quality are resolution, frame rate, and bitrate.
The concept of resolution, mentioned a little above, refers to the number of pixels in the video picture, which has a great impact on the fineness of the picture.
In the case of a certain video smoothness and monitor screen size, the resolution and quality of the video are directly proportional.
The frame rate is the rate at which the picture is played on the monitor, which determines whether the picture is smooth. But in general, at no less than 24 frames per second, our vision will not feel the pause of the picture, so the impact of this factor is relatively small.
Bitrate, also known as bitrate, refers to the amount of data of video clips per second, which is the main influencing factor of picture quality, the higher the bitrate, the greater the amount of data contained in the video, and the finer the content presented.
A simple and crude way to compare video quality is to look at the size of the file.
After all, the higher the image quality, the higher the bitrate, and the larger the storage space occupied.
For example, there is such a Blu-ray disc that burns the classic movie "The Godfather", and its bitrate is about 27Mbps, which means that the amount of video data per second is about 3MB.
Without counting audio, subtitles, the movie-only video in it also needs to occupy about 35GB of storage space.
The calculation method is as follows: video file volume = video bitrate * duration/8, that is:
27Mbps*173min*60s/8=35032.5MB
However, the Blu-ray 1080p movie video downloaded on a video website only takes up 1.6GB of space, which is the sum of various elements such as subtitles, audio, and watermarks.
Copyright images in the gallery are not authorized to be reproduced
Through calculation, it can be concluded that its bitrate does not even exceed 2Mpbs, indicating that the so-called Blu-ray 1080p on this video website is more than ten times different from the real Blu-ray video in bitrate.
Therefore, this can also explain why the Blu-ray is turned on on the video of some video websites but still blurs this problem -
Because they are not much clear, a large part of them are hanging sheep's heads to sell dog meat, and the difference between the real blue light is like the gap between the copycat version and the genuine version, which is purely a gimmick used by manufacturers to attract consumers.
Although the "Blu-ray" quality on some video websites is attractive, they may not be real Blu-ray, and even very different from the "real body".
If you want to feel the real Blu-ray quality, you may wish to find an original Blu-ray disc to experience it, I believe it will not disappoint you.
Audit expert: Zheng Yuanpan Professor of Zhengzhou University of Light Industry
Source: Digital Beijing Science Center