Connection and difference between video bit rate, frame rate, and resolution

 

Which of the following affects the definition of a movie? video bit rate, frame rate, and resolution?

Bit Rate: affects the volume, which is proportional to the volume. The larger the bit rate, the larger the volume. The smaller the bit rate, the smaller the volume.

Bit rate is the number of digits transmitted per unit time during data transmission. Generally, the unit is kbps, that is, a thousand bits per second. That is, the sampling rate (not equivalent to the sampling rate. The unit of sampling rate is Hz, indicating the number of samples per second). The larger the sampling rate per unit time, the higher the accuracy, the processed file is closer to the original file, but the file volume is directly proportional to the sampling rate. Therefore, almost all encoding formats focus on how to use the lowest Bit Rate to minimize distortion, based on this core, CBR (fixed bit rate) and VBR (Variable Bit Rate) are derived. "bit rate" is distortion. The higher the bit rate, the clearer the image. On the contrary, the image is rough and mosaic.

The following code rate and file size are calculated based on the sampling rate of a WAV file. The file information displayed by the mediainfo tool is as follows:

Summary

Complete name: audio \ WAV \ adele-rolling_in_the_deep.wav

File Format: Wave

File Size: 38.3 MIB

Length: 3 minutes 47 seconds

Average Mixed bit rate: 1 411 kbps

 

Audio

ID: 0

File Format: PCM

Format settings, endianness: Little

Encoding settings ID: 1

Encoding settings ID/prompt message: Microsoft

Length: 3 minutes 47 seconds

Bit Rate: 1 411.2 kbps

Audio channel: 2 audio channels

Sampling Rate: 44.1 kHz

Bit depth: 16 digits

Size: 38.3 MIB (100%)

 

1. Bit Rate Calculation formula:

Bit Rate = sampling rate X-bit DEPTH x-Channel

Therefore, the bitrate of the above file is 44.1 kHz x 16-bit x 2-channel = 1411.2 kbps

 

2. File size = bit rate x length= 1411.2 kbit/s X (3x60 + 47) S = 1411.2 kbit/s x 227 s

= 38102.4 KB

38102.4 KB/1024 KB/M = 37.2 m

The size of the file displayed by mediainfo is approximately 38.3 MB.

Note: This formula is effective for uncompressed WAV Files and does not apply to compressed files such as MP3 files.

Frame Rate: affects the smoothness of the image, which is directly proportional to the smoothness of the image. The larger the frame rate, the smoother the image. The smaller the frame rate, the more dynamic the image is. If the bit rate is a variable, the frame rate also affects the volume. The higher the frame rate, the more images pass through each second, the higher the bit rate and the larger the volume.

The frame rate is the number of frames transmitted in one second. It can also be understood that the graphic processor can refresh several times per second,

Resolution: affects the image size, which is proportional to the image size. The higher the Resolution, the larger the image. The lower the Resolution, the smaller the image.

Definition

When the bit rate is fixed, the resolution is inversely proportional to the definition. The higher the Resolution, the less the image is, the lower the resolution, and the clearer the image.
When the resolution is fixed, the bit rate is directly proportional to the definition. The higher the bit rate, the clearer the image. The lower the bit rate, the less unclear the image.

 

Bandwidth and Frame Rate

For example, if an image is transmitted over an ADSL line, the uplink bandwidth is only 512 kbps, but a four-way CIF resolution image needs to be transmitted. According to the general rule, the recommended bitrate for CIF resolution is 512 kbps. Therefore, only one channel can be transferred based on this computation. Reducing the bitrate will inevitably affect image quality. To ensure the image quality, we must reduce the frame rate. In this way, even the bit rate is reduced, the image quality will not be affected, but the image consistency will be affected.

Avi Frame Rate dwscale and dwrate

From: http://yixiangongzhu.blog.163.com/blog/static/19736320320111123111753465/

In msdn, dwrate/dwscale is the playback speed.
The number of frames played per second in a video may not be an integer, for example, 29.97,
Note that in the avistreaminfo structure, attributes are represented by integer variables, so decimals can only
Two integers (dwrate and dwscale) are used to obtain the playback speed.
For example, if the speed is 29.97, you can use dwrate = 2997, dwscale = 100 to get
If the speed is 29.9, you can use dwrate = 299, dwscale = 10 to get

The AVI file contains header information such as avimainheader and avistreamheader, including the following fields: Start, length, scale, and rate, which are described as follows:

In avimainheader:

TheDwstartAndDwlengthFields specify the starting time of the AVI file and the length of the file. The units are definedDwrateAnd
Dwscale.DwstartField is usually set to zero.

TheDwscaleAndDwrateFields are used to specify the general time scale that the file will use. In addition to this time scale, each stream can have its own time scale. The time scale in samples per second
Is determined by dividingDwrateByDwscale.

In avistreamheader:

DwscaleIs used togetherDwrateTo specify the time scale that this stream will use.

DividingDwrateByDwscaleGives the number of samples per second.

For video streams, this rate shocould be the frame rate.

For audio streams, this rate shocould correspond to the time neededNblockalignBytes of audio, which for PCM audio simply CES to the sample rate.

 

For understanding, let's take an actual AVI file for analysis:

1. Video avistreamheader: length = 4500, scale = 1, rate = 25. Therefore, the video frame rate of this file is 25/1 = 25. The video duration is 4500/25 = 180 seconds. These numbers are easy to understand.

2. audio avistreamheader: length = 2812, scale = 16000, rate = 2. When you first read the data and carefully analyze it, you can understand that for PCM audio, nblockalign is equal to dwsamplesize, 2, and each audio sample is two bytes, the size of each audio frame is 16000/2 B, and dwrate/dwscale is the sampling rate: 8000 =, so the audio duration:

(2812*1024/2)/(16000/2) = 179.968 seconds.