The concept of streaming media audio and video technology parameters and the detailed tutorial

resolution Concept

Resolution is an important concept related to image, which is the technical parameter to measure the expressive force of image detail. High resolution is an important prerequisite to ensure the clarity of color display. Resolution is to reflect the precision of the screen image, refers to the display can display the number of points. Generally, "Resolution" is represented as the number of pixels in each direction, the higher the resolution, the more points can be displayed, the more refined the screen.

Video resolution refers to the size or size of the image that the video imaging product is made of. At present, mobile phone station Common visual resolution has 480x270, 640x360,1024x768. The screen aspect ratio is 16:9 and 5:4.

Code Rate Concept

Code rate (data Rate), the code rate is the number of times transmitted by unit time, generally we use the unit is Kbps is thousands per second. He is the most important part of the image quality control in video coding. At the same resolution, the larger the code stream of the video file, the smaller the compression ratio, the higher the picture quality.

Code Rate Unit

Kbps: The first thing to understand is that PS refers to/s, that is, per second. Kbps refers to the speed of the network, that is, the number of thousands of messages per second (k for thousands, KB is the number of thousands of bits), in order to visually appear faster transmission of the network, the average company is used in kilobytes (thousands) to represent. 1kb/s=8kbps. ADSL Internet speed is 512Kbps, if converted to bytes, is 512/8=64kb/s (that is, 64,000 bytes per second).

Frame rate Concept

The frame rate is the number of images per second, and the resolution indicates the size of each image, that is, the number of pixels, stream is the amount of data produced per second after video compression, and compression is to remove the space redundancy and video time redundancy, so, for static scenes, you can use very low code flow to obtain better image quality, and for the scene of vigorous movement, It is possible to use a high stream of code to not achieve good image quality, so the conclusion is to set the frame rate that you want real-time, set the resolution is the size of the image you want to see, and the setting of the rate depends on the camera and scene conditions, through the field debugging, until an acceptable image quality, you can determine the size of the code flow.

A frame is a static picture, continuous frames to form animation, such as television images. We usually say that the number of frames, simply, is the number of frames that are transmitted in 1 seconds, and it can be understood that the graphics processor can refresh several times per second, usually with FPS (Frames/Second). Each frame is a stationary image, and a quick and continuous display of frames forms the illusion of motion. A high frame rate allows for smoother, more realistic animations. The greater the number of frames per second (fps), the smoother the actions displayed.

the relationship between frame rate resolution and code flow






Sample Rate

Defines the number of samples per second that are extracted from a continuous signal and composed of discrete signals, which are expressed in hertz (Hz). The reciprocal of the sampling frequency is the sampling period or the sampling time, which is the time interval between the samples. The popular speaking sampling frequency is refers to the computer each second gathers how many sound samples, is describes the sound file the quality, the tone, the measurement sound card, the sound document standard.

In today's mainstream acquisition card, sampling frequency is generally divided into 22.05KHz, 44.1KHz, 48KHz three levels, 22.05KHZ can only achieve FM broadcast sound quality, 44.1KHz is the theoretical CD quality limit, 48KHz is more accurate. For more than 48KHz of the sample frequency of human ears can not be identified, so there is not much value on the computer.

Streaming media Audio and video format

Streaming Media Video format H.264

H.264 is a new generation of digital video compression format, which is proposed by the International Organization for Standardization (ISO) and ITU (ITU) H.264 the most valuable part of the MPEG4 is undoubtedly the higher data compression ratio. Under the same image quality conditions, the H.264 data compression ratio can be 2-3 times higher than the MPEG-2 used in the current DVD system, 1.5-twice times higher than the MPEG-4. Because of this, after H.264 compressed video data, in the network transmission process needs less bandwidth, but also more economical. When the MPEG-2 requires a 6Mbps transmission rate match, the H.264 only needs the 1mbps-2mbps transfer rate.

Streaming Media Audio format

AAC (Advanced Audio Coding) A file compression format specifically designed for sound data, unlike MP3, it uses a new algorithm for coding, more efficient, and has a higher "price/performance". Using AAC format can make people feel the sound quality is not significantly reduced under the premise of more compact