Frame rate, code stream and resolution

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One, frame rate, code flow and resolution

Frame rate Concept

A frame is a static picture, a continuous frame to form an animation, such as TV images. We usually say that the number of frames, in short, is how many pictures are transmitted in 1 seconds, and it can be understood that the graphics processor can refresh several times per second, usually expressed as FPS (Frames per Second). Each frame is a stationary image, and a fast and continuous display of frames creates the illusion of motion. The high frame rate allows for smoother, more realistic animations. The greater the number of frames per second (fps), the smoother the displayed action will be.

Stream concept Stream (data rate), refers to the video file in a unit of time to use the traffic, also known as the code rate, is the video coding in the picture quality control of the most important part. At the same resolution, the larger the stream size of the video file, the smaller the compression ratio, and the higher the picture quality.

Resolution concept video resolution refers to the size or size of an image of a video imaging product. The common image resolution is 352x288,176x144,640x480,1024x768. In the image of the two sets of numbers, the former is the image length, the latter is the width of the picture, the two are multiplied by the image of the pixel, the aspect ratio is generally 4:3.

Second, using the stream and time to calculate the size of the streaming media file

The encoding rate/bit rate is directly related to the file volume. and the encoding rate and encoding format is appropriate, directly related to the video file is clear.
In the field of video coding, bitrate is often translated to encoding rate, in Kbps, e.g. 800Kbps
Among them, 1k=1024 1m=1024k
B is bit (bit) This is the computer file size of the unit of measure, 1kb=8kb, case-sensitive, b for byte (byte)
S is seconds (second)
P for each (per)
A 800kbps encoding means that the encoded data needs to be represented by 800K bits per second.

1mb=8mb=1024kb=8192kb

Windows system file size is often expressed in B (bytes), but network operators with B (bit), that is why 512K speed broadband on the computer to show the fastest only about 64K reasons, network operators to promote the speed of the time omitted the unit of measurement.
The complete video file is composed of 2 parts of the audio stream and the video stream, and the audio and video respectively use different encoding rates, so the encoding rate of the final technology size of a video file is the audio encoding rate + video encoding rate. For example, an audio encoding rate of 128Kbps, the video encoding rate of 800Kbps files, the total encoding rate of 928Kbps, meaning that the encoded data needs to be expressed in 928K bit per second.
After understanding the meaning of the encoding rate, it is not difficult to understand and calculate the size of the final file depending on the length of the video playback time. The encoding rate is also high, the longer the video playback time, the larger the file volume. Not the larger the resolution, the larger the file, just under normal circumstances, in order to ensure clarity, higher resolution requires a higher encoding rate, so that people produce a larger resolution of the video file the greater the sense of volume.

Calculate the output file size formula:
(Audio encoding rate (kbit)/8 + video encoding rate (kbit)/8) x Total movie length (seconds) = File size (MB)

In this way, you can control the output file size accurately.
Example: There is a 1.5-hour (5,400-second) movie, hoping to convert the file size to just 700M
The calculation method is as follows:
700x8÷5400x1024≈1061kbps
This means that as long as the audio encoding rate plus the video encoding rate of the sum of 1061Kb, then the 1.5-hour movie converted file size is exactly 700M.

As for the audio encoding rate and video encoding rate specific how to set, it depends on the choice of encoding format and personal preferences, as long as the sum of 2 is 1061. such as can be set to video encoding format H264, video encoding rate of-Kbps, audio encoding format AAC, encoding rate 161 Kbps.
The bitrate associated with the size of the file refers to the average bitrate, so the file size can be guaranteed, whether using a fixed bit one-time encoding or two times (multiple) dynamic encoding. The file size is not controllable until you use a quality-based encoding method.

There are many coding formats, and in the case of continuous improvement of technology, various coding formats are produced for different purposes. Different encoding format of the compression rate is not the same, and have their own characteristics, some in the low bit rate situation can maintain a higher picture quality, but in the case of high bitrate but the picture quality is not very good, some suitable for high-bit rate situation to maintain high-definition screen, but may be poor in low bit rate situation. introduces several common ones.
Rmvb/rm in the formulation of the main consideration is the network communication, the purpose is to use the unpleasant speed of transmission of visual acceptable picture quality. Therefore, the RMVB/RM encoding format is characterized by better video quality at lower bit rates. But the case of high bit rate is inferior to other encoding format. Also is the RM/RMVB suffix file, its internal encoding format subdivision also has R8/R9/R10 and so on, but overall, the above mentioned characteristic still exists. Just the compression rate is higher, so rmvb no one is used in the HD coding field. RMVB the pursuit of high compression rate, acceptable picture quality, so often compress some of the details are not easy to notice. First look at the picture is good, see the picture is not sharp, the level is not clear, always give people always vague feeling. RMVB/RM suffix file Audio encoding part of the same situation, the sound compression rate is very high, but only can listen, do not expect to reach the sound of the state. The popularity of RMVB is due to the fact that this format is suitable for low-speed networks, which can receive acceptable picture quality in smaller file sizes. Second, with the use of RMVB, began to appear functions of the more complete transcoding software and solutions, convenient for video enthusiasts, expanded the source of the film. But with the faster speed, H264 and other better encoders appear, but also because RMVB is not suitable for high-definition video production, and if the other hardware manufacturers want to support the RMVB/RM format, it is necessary to pay the real company a very expensive patent fees, causing many hardware manufacturers to abandon the support of rmvb files. RMVB's files are no longer the overwhelming advantage of the past. Now the network spread video file already many are AVI, MKV, MP4, 3GP and so on suffix. Which MKV and other for high-definition video files, MP4, 3GP and other applications for mobile phones and portable devices and other fields, AVI is more widely used, not only in high-definition video files have AVI files, in the Portable Device field also has AVI use.
VCD with video encoding format for Mpeg1,dvd, MPEG2,VCD and DVD are mainly used for home audio and video playback, and generally speaking, VCD with MPEG1 encoding fixed code rate encoding. DVD can support MPEG2 encoding of dynamic bitrate. In order to guarantee the sharp change in the time of the sharpness of the screen, its default encoding rate is relatively high, VCD standard encoding rate of 1152KBPS,DVD open some, according to the film playback time, often set to Kbps-8000 Kbps, Use a higher bitrate to achieve higher clarity without wasting DVD disk capacity. MPEG1 and MPEG2 in the ultra-low rate of the effect of the situation, and excessive increase in the code rate, the screen effect brings the hint is not obvious.