Why is the Blu-ray I watch not as clear as 720P? My membership is in vain...

Audit expert: Zheng Yuanpan, professor at Zhengzhou University of Light Industry

Surprise check! How many video websites have you purchased memberships for? As a TV drama lover, have you unlocked the ultra-high definition on each website? You may have noticed that since when, several mainstream video websites have marked different levels of video clarity below the videos.

Initially, there were three levels of video clarity: standard definition, high definition, and ultra-high definition. Later, Blu-ray 1080p and 4K quality were added exclusively for members. However, these quality levels are often different on major video websites, which makes people dazzled and confused.

Source: pixabay

What is the secret of video clarity? What is "Blue Ray"? Sometimes, even if some videos are played with Blue Ray, the picture quality is still blurry and the clarity is not satisfactory. Why is this? Don't worry, the editor will take you to find out!

The quality levels of some video sites

Source: Screenshot from video website

I believe that everyone is familiar with the word resolution . It is the decisive factor in the clarity of the video. This indirectly leads many friends to equate the picture quality we often say, such as 720p, 1080p, etc., with resolution.

In fact, at the beginning, the expression "digital + p" did not refer to a fixed resolution, but a video display format . The p here refers to the number of vertical pixel rows of the display, and 720p means 720 rows. Later, this concept was extended to the digital film standard, which became the relevant definition of video resolution.

Resolution diagram source: Wikipedia

According to the current resolution specifications in the video industry, standard definition refers to video formats with a physical resolution below 720p, which has low clarity. 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 aspect ratio of the video is 16:9.

HD includes 720p, 1080i and 1080p. Unlike the above, p and i here represent progressive scanning and interlaced scanning respectively. Under the same resolution, the quality of progressive scanning is better than that of interlaced scanning.

Generally speaking, only a resolution of 720p or above can be called a high-definition signal source. Correspondingly, industry insiders call 720p standard high-definition, while 1080i and 1080p are called full high-definition. Different from the industry standard, the ultra-high-definition quality displayed on video websites generally refers to 1080p full high-definition quality, while high-definition quality generally refers to 720p.

Source: pexels

Seeing this, many friends may ask, what are Blu-ray and 4K?

Blu-ray, also known as Blu-ray Disc, is a storage disc . It uses a shorter wavelength blue laser to read and write data, so we call it "Blue-ray". But unlike the HD and UHD mentioned above, it does not refer to a specific video definition. Blu-ray discs have a large storage capacity, generally dozens of GB, so they can store some videos with high bitrate and good picture quality.

4k video refers to a video with a resolution of 3840×2060, also known as 2060p. It has 4,000 pixels horizontally and a total of more than 8 million pixels. It is one of the digital videos with the highest resolution at present, with high clarity and excellent viewing experience.

Schematic diagram of the effects of different resolutions

Source: Wikipedia

On some video websites, Blu-ray 1080p is often used as a higher definition level, which requires membership privileges to watch or cache. So what is Blu-ray quality? What is the difference between Blu-ray on video websites and real Blu-ray quality?

Generally speaking, the main factors affecting image quality are resolution, frame rate and bit rate.

The concept of resolution was briefly mentioned above. It refers to the number of pixels in a video image, which has a great impact on the fineness of the image. When the video smoothness and the display screen size are constant, the video resolution and image quality are proportional.

The frame rate is the speed at which the image is played on the monitor, which determines whether the image is smooth. But generally speaking, if it is not less than 24 frames per second, our vision will not feel the image is jerky, so the impact of this factor is relatively small.

Bit rate , also known as bit rate, refers to the amount of data in a video clip per second. It is the main factor affecting the image quality. The higher the bit rate, the more data the video contains, and the more detailed the content presented. If you want to compare video quality, there is a simple and crude way, which is to look at the file size. After all, the higher the image quality, the higher the bit rate, and the more storage space it occupies.

Source: pixabay

For example, there is a Blu-ray disc with the classic movie "The Godfather" burned on it. Its bit rate is about 27Mbps, that is, the amount of video data per second is about 3MB. Without calculating audio and subtitles, the pure video of the movie also takes up about 35GB of storage space.

The calculation method is as follows: Video file size = video bit rate * duration / 8

That is: 27Mbps*173min*60s/8=35032.5MB

However, a Blu-ray 1080p movie of the same length downloaded from a certain video website only occupies 1.6GB of space, including subtitles, audio, watermarks and other miscellaneous elements. Through calculation, it can be concluded that its highest bit rate does not exceed 2Mpbs, which means that the so-called Blu-ray 1080p on this video website is more than ten times different from the real Blu-ray video in bit rate.

Therefore, this can also explain why the videos on some video websites are still blurry even after turning on the Blu-ray - because they are not very clear to begin with, and a large part of them are just wolves in sheep's clothing. The difference between them and the real Blu-ray is like the difference between a copycat version and an authentic version, and it is purely a gimmick used by manufacturers to attract consumers.

Although the "Blu-ray" images on some video websites are attractive, they are not necessarily real Blu-rays, and are even very different from the "real thing". If you want to experience the real Blu-ray image quality, you might as well find an original Blu-ray disc to experience it. I believe you will not be disappointed.