Tag: what mp3 bitrate should i use

What is the bit rate, which is said to be indispensable for video distribution?

1Bit rate is the number of bits that can be sent and received per second.

Advantages and Disadvantages of Setting a High Video Bitrate
# There are merits such as being able to offer clearer images
#There are disadvantages such as not being able to play fluently
Five What are the factors that affect the image quality of videos?

#frames per second
#resolution
#Codec
6 Relationship between YouTube and bit rate
7 Relationship between video conferencing and bit rate
8summary
One of the important factors affecting the image quality of a video is the “bit rate”. Generally, the higher the video bit rate, the better the image quality. But what is the bitrate of the video? How should I set the bitrate of the video? I wonder if there are a lot of people worried. In this article, we will discuss video and audio bit rates, video bit rate guidelines, advantages and disadvantages of setting a high video bit rate, factors that affect video quality, the relationship between YouTube and bit rates and video conferencing. about.

Bit rate is the number of bits that can be sent and received per second.

Bit rate refers to the number of bits that can be sent and received per second, and the unit is bps, which is short for Bit Per Second.

For example, if it is 100 bps, it means that 100 bits of data can be sent and received per second.

The higher the bit rate value, the more data can be sent and received per second. Video bit for bit rate

There are two types, audio bit rate and rate, and the value calculated by adding these two bit rates is called the oval bit rate.

# Voice bit rate

The audio bit rate refers to the bit rate related to the audio in the video file, and basically the value of the audio bit rate is less than the bit rate of the video. As a guideline for audio bit rate, it is approximately 96 to 128 kbps for lossy codecs such as MP3 and AAC, while it is approximately 192 to 320 kbps for high-quality video.

# Video Bitrate

Video bit rate refers to the bit rate associated with video in a video file. The video bit rate value is large compared to the audio bit rate. The guideline for video bit rate varies greatly depending on the quality of the image to be delivered, and the value varies, but it is also said to be 500 kps at 70 Mbps.

Since the standard audio bit rate is approximately 192 to 320 kbps, the video bit rate occupies most of the oval bit rate when watching the entire video file. Basically, the characteristic of video bitrate is that the higher the value, the better the image quality.

However, it does not mean that the video bit rate value should be high. When viewing an image on a small monitor screen, it can be said that the roughness of the image is not that noticeable even if the bitrate value is a bit low. Even if you increase the value of the video bit rate, you cannot get the feeling that the image quality has improved, and there are many cases where the file size just increases.

Estimated video bit rate
Even if the bit rate value is the same, the image quality will change depending on whether the video content is moving or not. Therefore, it is necessary to determine the bitrate that appears to be optimal for the video. The following is a guide to the proper bit rate for frequently used video resolution when distributing videos on YouTube.

Resolution SD (720 x 480px) 1-2 Mbps (video with a lot of movement) 500kps ~ 1Mbps (video with little movement)
HD resolution (1280 x 720px) 4.5-9Mbps (video with a lot of movement) 2.4-4.5Mbps (video with little movement)
Full HD resolution (1920 x 1080px) 9Mbps-18Mbps (high-motion video) 4.5-9Mbps (low-motion video)
4K resolution (4096 x 2160px) 35 ~ 70Mbps (high motion video) 25-35Mbps (low motion video)

H.266 video encoding method

| It was successful in transmitting 4K / 60fps video using a VVC compliant real-time codec – It is possible to provide highly realistic video services at a bit rate less than half that of the method.

KDDI R&D Laboratories, Inc. (Headquarters: Fujimino City, Saitama Prefecture, Director: Gen Nakamura, hereinafter “KDDI R&D Laboratories”) is the latest international standard H.266 video encoding method | VVC (Versatile Video Coding) Using a real-time codec system (hereinafter “this system”) compatible with “VVC”), we achieved a demonstration experiment of streaming 4K video at a bit rate of 12 Mbps (megabit / sec) and a frame rate of 60fps (frames / sec.) We have confirmed that stable video quality can be maintained even if the bit rate is reduced to less than half that of the current stream.
Current 4K streaming video is streamed at a frame rate of 60fps, and by using this system, viewers can be provided with a highly realistic video service comparable to 4K streaming, including not only streaming but also mobile lines. . provide a more flexible network configuration.

[Background]
KDDI R&D Laboratories is dedicated to the research and development of compression technology with the aim of realizing a content experience that maintains a high sense of presence by providing the optimal transmission media according to the situation of the user who is viewing the video. Is working.

1. 1. This demo experiment follows the following two VVC research results announced by KDDI R&D Laboratories in September and December 2020.
・ Developed the world’s first newest video encoding method H.266 | VVC Compliant 4K Realtime Encoder (September 1, 2020)
・ The world’s first newest video encoding method H.266 | VVC Compatible Realtime Codec 4K Live Streaming Successful Demo Experiment (Dec 23, 2020)

2. VVC is the latest video encoding method, and is the international standard video encoding method widely used in today’s Internet 4K / 8K video transmission and distribution services. H.265 | HEVC (High Efficiency Video Coding, hereinafter “” Achieves twice the video compression performance of “HEVC”). It was standardized in August 2020 by the international standardization bodies ITU-T and ISO / IEC. In Japan, its adoption is being considered as one of the video coding methods in the sophistication of terrestrial digital television broadcasting, which is being studied by the Ministry of the Interior and Communications (Note 1).

The 3.4K video streaming has a frame rate of 60fps and is superior in reproducibility of high-speed moving scenes compared to 30fps, which is generally used for Internet video distribution, especially in sports scenes. It helps to improve the quality of the experience. In the experiments so far, it was aimed at 30fps and it was difficult to use it for streaming.

[Scheme and results of the demonstration experiment]
On December 21, 2021, a network line was used from Kansai Television Broadcasting Corporation (Kita-ku, Osaka) to the KDDI Research Workshop (Minato-ku, Tokyo) using this system developed by KDDI R&D Laboratories. a video streaming demonstration experiment over.

In the demo experiment, we managed to stream 4K video at 12 Mbps bit rate and 60 fps frame rate, and confirmed that stable video quality can be maintained even if the bit rate is reduced to less than half of the current one. transmission.
We have improved acceleration processing and parallelization processing that are effective for making VVC encoders on multi-core CPU platforms, and we have devised and realized technology that scales not only at a frame rate of 30fps but also at 60fps. .

Factors related to the quality of video and audio data Part 2

resolution
This is also an item dedicated to video.

Resolution is a numerical value that represents the density of pixels in an image. We use the unit “dpi (dots per inch)” or “ppi (pixels per inch)”. The “image” in digital is expressed by “a collection of very small colored dots (pixels).” The higher the resolution value, the higher the density of this point and the finer and more natural the image will be.

There is also a concept similar to this, which is the concept of resolution using pixels (dots, pixels). Uses pixels [pixel], dots [dot], or pixels as the unit. It is often written as “1920 x 1080 pixels” or “2 million pixels”, and in the case of this video, there are “1920 horizontal and 1080 vertical color points (pixels), and the total number of points is 2,073,600 ( approximately). It means “2 million pieces)”. (* Pixel = dot = pixel)

For resolutions that use “dpi”, it represents the density of pixels per 1 inch (= 0.0254 meters) of a straight line.
For resolutions that use “pixels”, it represents the total number of pixels used in the video.

The exact definition of resolution is the first. However, the latter is also widely recognized. Be careful not to get confused.

▲ Source: Wikipedia “Resolution”

Screen resolution / ratio
In the field of displays, there is also “screen resolution”. This is represented by pixels. Because it uses pixels, it represents the total number of pixels on the screen. You can also express the “screen aspect ratio (screen aspect ratio)” by multiplying it by something like “1920 x 1080 pixels”. If it is “1920 x 1080 pixels”, the aspect ratio of the screen is “16: 9”.

If the aspect ratio of the image and the aspect ratio of the screen do not match, black bands may appear at the top and bottom or left and right when the image is fully displayed (enlarged display), or the image may be to stretch.

Some screen aspect ratios have special names. The following are pixel counts, screen aspect ratios, and commonly used screen names. (* Since most pixel ratios are square, screen aspect ratio = screen aspect ratio)

Known as Horizontal x Vertical Ratio
(horizontal: vertical) Number of pixels
VGA 640 × 480 4: 3 307,200
SVGA 800 × 600 4: 3 480,000
XGA 1024 × 768 4: 3 786,432
SXGA 1280 × 1024 5: 4 1,310,720
WSXGA + 1680 × 1050 16:10 1,764,000
FHD (Full HD) 1920 × 1080 16: 9 2,073,600
WUXGA 1920 × 1200 16:10 2,304,000
Wikipedia: screen resolution that

By the way, continuing from last time, there is too much basic knowledge and it seems frustrating, but please do your best. Knowing this and not knowing it will make a big difference in your video and audio conversion and playback work. Remember it little by little as it is a necessary knowledge to be able to play and convert optimally while maintaining quality without waste.

Factors related to the quality of video and audio data

Last time, I wrote about “codecs” and “containers” that determine the format of the video and audio data. Now, I would like to write about each item related to the “quality” of that data.

Bit rate
Bit rate [bit rate], or bits per second, is a unit of data transfer rate.
It is defined as the number of bits that have passed (transferred) at a given point on the data transfer path per second. Also known as bps [bits per second] and b / s. Other names include “bit rate” and “bit efficiency”, all of which have the same meaning.

In short, it is a unit that expresses “how much data (information) can be transferred”. A large number means that the amount of data passed at a certain point is large and the quality of the video and audio is improved. The greater the amount of data (that is, video / audio information), the higher the image quality and sound quality.

An SI prefix can also be added, and the unit is as follows.

Bits per second [bps: b / s]
Kilobit per second [kbps: kb / s]
Megabit per second [Mbps: Mb / s]
Gigabit per second [Gbps: Gb / s]
Since it is a unit of data transfer speed, it is also used for the speed of Internet lines. There is also a unit called bytes per second, which is expressed as “Bps” or “B / s” by capitalizing b. 1 byte = 8 bits.

For example, with MP3 audio data, the bit rate value can be increased up to “320 kbps”. The higher the number of bit rates, the greater the amount of data transferred and the greater the original data capacity.

The phrase “high bit rate” is essentially incorrect
I often hear the phrase “high / low bit rate”, but this phrase is really inappropriate.

The word bit rate is a unit, not a physical quantity. It is the same as the relationship between “length (physical quantity)” and “meter (unit)”. We say “long” but not “long meter”.

The physical quantities that represent bit rates are called “transfer rate”, “transfer speed”, “transfer efficiency”, “transmission rate”, “transmission speed”, “transmission efficiency”, and so on. However, the phrase “high bit rate” has become mainstream, so you don’t need to worry too much about it. Remember “To be exact …”.

frames per second
This is a value for video data only.

The frame rate [frame rate] is an index that shows how many frames (still images: frames) can be processed per unit of time. Use fps [frames per second] or f / s as the unit.

Digitally speaking, a video is not recorded as a continuous image, but is taken continuously and displayed at high speed like a flip book, so that it “appears to be moving.” I’m doing. It is a method that uses the effect of human residual image.

The “one-by-one still images” are called “frames” or “frames.”

If the frame rate value is large, the number of processed frames per second will increase, resulting in smoother video. If it is 30 fps, 30 frames per second are processed.
Currently, “30 fps” or “29.97 fps” is very widespread. When you increase to 60fps, the video becomes smooth enough and when you decrease to 15fps or less, the video becomes jerky.

Increasing the value of the frame rate will result in a smoother video, but it will be heavier and of higher capacity.

There is no point in raising him innocently

There is no doubt that increasing the value of the frame rate will result in a smoother video, but if the value called “response speed” of the screen or monitor displaying the video is large (that is, slow), the frame rate value will be increased. It may not make sense to increase it.

Response speed is the time it takes for a signal to actually enter. The unit is milliseconds [ms: 1 ms is 1/1000 second of 1 second]. The “Response Speed” on a screen or monitor indicates the speed when changing from “black to white to black”. (Currently the definition is blurry because it handles colors other than black and white, but it is omitted here.)

If this response speed is high, it means that the video (color) change is fast. If the speed is high, the response speed value will be small and it will be able to display “smooth and clear video, even when moving fast.” At low speeds, the value increases and “residual images are likely to occur in videos being played.