in the field of video coding, bit rate is often translated into coding rate, and the unit is Kbps, for example, 8Kbps
where 1K=124 1M=124K
b is the unit of measurement of computer file size, 1KB=8Kb, which is case-sensitive, and b stands for Byte) s is second.
1mb = 8mb = 124kb = 8192kb
The file size of Windows system is often expressed in B (bytes), but the network operators use B (bits), which is why the fastest display speed of 2Mb broadband on the computer is only about 256KB. When network operators advertise the network speed, they omit the measurement unit.
A complete video file consists of two parts: audio stream and video stream. Audio and video use different coding rates, so the final technical coding rate of a video file is audio coding rate+video coding rate. For example, a file with an audio encoding rate of 128Kbps and a video encoding rate of 8Kbps has a total encoding rate of 928Kbps, which means that the encoded data needs to be represented by 928kbits per second.
after understanding the meaning of coding rate, it is not difficult to understand and calculate the final file size according to the length of video playback. The coding rate is also high, and the longer the video playback time, the larger the file size. It's not that the larger the resolution is, the larger the file will be. It's just that in general, in order to ensure clarity, a higher resolution requires a higher coding rate, which makes people feel that the larger the resolution is, the larger the video file will be.
formula for calculating the output file size:
(audio coding rate (Kbit) /8+video coding rate (Kbit) /8)× total movie length (seconds) = file size (MB)
So that everyone can accurately control the output file size in the future.
example: there is a 1.5-hour (54-second) movie, and it is hoped that the converted file size will be just 7M
The calculation method is as follows:
7×8÷54×124≈161Kbps
It means that as long as the sum of the audio coding rate and the video coding rate is 161Kb, it will be 1.
how to set the audio coding rate and video coding rate depends on the selected coding format and personal preference, as long as the sum of them is 161. For example, it can be set to video coding format H264, video coding rate of 9 Kbps, audio coding format AAC, and coding rate of 161 Kbps.
The code rate related to the file size refers to the average code rate. Therefore, the file size can be guaranteed whether the fixed bit primary coding method or the secondary (multiple) dynamic coding method is used. Only when quality-based coding is used can the file size be uncontrollable.
there are many coding formats. with the continuous improvement of technology, various coding formats have been produced for different purposes. Different coding formats have different compression rates and have their own characteristics. Some of them can maintain high picture quality at low bit rate, but the picture quality is not very good at high bit rate. Some of them are suitable for maintaining high-definition pictures at high bit rate, but the effect may not be good at low bit rate. Introduce some common ones.
when p>RMVB/RM is formulated, the main consideration is network communication, aiming at spreading the visually acceptable picture quality by using the unpleasant network speed. Therefore, the characteristic of RMVB/RM coding format is that it can obtain better video quality at lower bit rate. But in the case of high bit rate, it is not as good as other coding formats. For files with RM/RMVB suffix, there are R8/R9/R1 and other internal coding formats, but generally speaking, the above characteristics still exist. Only the compression ratio is higher, so RMVB is not used in the field of high-definition coding. RMVB pursues high compression ratio and acceptable picture quality, so it often compresses some details that are not easy to pay attention to. At first glance, the picture is good, but when you look closely, you will find that the picture is not sharp and the level is not clear, which always gives people a vague feeling. The same situation exists in the audio coding part of RMVB/RM suffix file. The sound compression rate is very high, but it can only be heard. Don't expect to reach the realm of beautiful sound.
the popularity of p>RMVB is due to the fact that this format of REAL is suitable for the spread of low-speed networks and can obtain acceptable picture quality with a small file size. Second, with the use of RMVB, transcoding software and solutions with relatively perfect functions began to appear, which facilitated video lovers and expanded the source of movies. However, with the increasing network speed, better encoders such as H264 appear, and at the same time, because RMVB is not suitable for high-definition video production, and if other hardware manufacturers want to support RMVB/RM format, they must pay a very expensive patent fee to REAL, which leads many hardware manufacturers to give up their support for RMVB files. RMVB files are no longer the overwhelming advantage they used to be.
nowadays, many video files spread on the internet are suffixes such as AVI, MKV, MP4 and 3GP. Among them, MKV is mostly used for high-definition video files, MP4 and 3GP are mostly used for mobile phones and portable devices, and AVI is widely used, not only in high-definition video files, but also in portable devices.
the video coding format used for VCD is MPEG1, while that for DVD is MPEG2. both VCD and DVD are mainly used for home audio and video playback, and generally speaking, vcd is coded with MPEG1 as a fixed bit rate. DVD can support MPEG2 coding with dynamic bit rate.
in order to ensure the clarity when the picture changes drastically, the default coding rate is high. The standard coding rate of VCD is 1152Kbps, and the DVD is open, which is usually set to be between 5kbps and 8kbps according to the movie playing time. Under the premise of not wasting the capacity of DVD, the higher coding rate can be used as much as possible to obtain higher clarity. MPEG-1 and MPEG-2 are not effective in the case of ultra-low bit rate, and the prompt brought by the picture effect is not obvious when the bit rate is excessively increased. MKV, on the other hand, is coded in H.264, which is used for high-definition video, and the code rate of 18p picture reaches 3Mbps.
Of course, the calculation formula of uncompressed files is different:
For sound, the data amount (bits/second) = (sampling frequency (Hz)* sampling bits (bit)* number of channels)
Among them, the number of channels in mono is 1 and the number of channels in stereo is 2.
amount of data * time/8 = total bytes of the file
For example, a CD is an uncompressed audio file, with a sampling of 44.1k,16 bits and two channels.
the amount of data = 44.1 * 16 * 2 = 1411kb/124 = 1.38mb, and the average MP3 is 128kbps
If one CD is put for one hour, the total number of CDs is = 1.38 * 36/8 = 7MB, of course, the CD will be put for more than one hour, at most.
the image should be, data amount (bit/sec) = (picture size * color bit)* frame number)
data amount * time/8 = total file bytes
for example, 2 minutes, 25 frames/sec, 64×48 resolution, and the uncompressed data amount of 24-bit true color digital video is about. The standard encoding rates of VCD and MKV (plus audio) are 1152Kbps and 3Mbps(18p HD)
2-minute file bytes = 18m bx12/8 = 27kb = 2636.7875mb = 2.57GB, and a 9-minute high-quality DVD movie can reach 9GB after compression.
definition of data density: average code stream allocated to one unit pixel in each frame of video
formula: data density = bits/(pixel * frame)
bits: video bit rate
pixel: pixel, horizontal pixel× vertical pixel
frame: frame rate, Generally, it is 23.976fps, 24fps (part of Hong Kong and Taiwan BD) and 25fps (area 2 and area 6 BD)
From the formula of data density, the video definition is
1. In the case of fixed bit rate (such as HALFCD, fixed at 48-52kbps, MINISD, fixed at 8-1kbps)
. The clearer it is, such as the HALFCD of 64*256, the MINSD of 8*336 < P > 2, and the boundary between HD and SD < P >. The high-definition sensory standards obtained are 72p and 18p, and the data density is .25-.35 and above, so the bit rate is about 5Mb/1Mb and above, which is representative. The SD sensory standards obtained by BD72p/BD18p
of each HD group are a48p and 48p, and the data density is .12-.18 and above, so the bit rate is about 12-25kbps. Representative works, BDRip/DVDRip
Discussion II: Preface of MEGUI suppression template and parameter setting. P frame is an inter-frame image data compression with reference to I frame, not an independent frame. Most of the compressed videos are P frames, so the video quality is mainly represented by P frames. Because P frame is not an independent frame, but only saves the difference with the adjacent I frame, there is actually no concept of resolution, and it should be regarded as a binary difference sequence. However, when using entropy coding compression technology, the binary sequence will use quantization parameters for lossy compression, and the video quality is directly determined by quantization parameters, which will directly affect the compression ratio and bit rate. Video quality can be expressed in subjective and objective ways, the subjective way is usually referred to as video clarity, while the objective parameters are quantization parameters or compression ratio or code rate. On the premise that the video source is the same and the compression algorithm is the same, there is a direct proportional relationship between quantization parameters, compression ratio and bit rate.
Video bit rate
Information in a computer is represented by binary zeros and ones, where each zero or one is called a bit and is represented by lowercase b, that is, a bit; Capital b represents byte, that is, byte, and one byte = eight bits, that is, 1b = 8b; The capital k in front means thousands, that is, thousands of bits (Kb) or thousands of bytes (KB). Represents the size unit of a file, and generally uses bytes (KB) to represent the size of a file.
Kbps: the first thing to understand is that ps refers to /s, that is, every second. Kbps refers to the network speed, that is, how many kilobits of information are transmitted per second (K means kilobits, Kb means how many kilobits). In order to visually appear that the network transmission speed is faster, general companies use kb (kilobits) to express it. If it is KBps, it means how many kilobytes are transmitted per second. 1KBps＝8Kbps。 When ADSL accesses the Internet, the network speed is 512Kbps. If it is converted into bytes, it is 512/8 = 64 kbps (that is, 64 kilobytes per second).