audio

  • PCM: Pulse Code Modulation. Analog signals are converted into digital signals by sampling, quantization and coding. According to Nyquist sampling theorem, in order to restore the analog signal without distortion, the sampling frequency should not be less than 2 times of the highest frequency in the analog signal spectrum.

  • Sampling rate: the frequency of sampling. Because the sampling rate is twice larger than the original acoustic frequency, and the highest frequency that human ear can hear is 20kHz, in order to meet the auditory requirements of human ear, the sampling rate should be at least 40kHz, usually 44.1kHz, and higher usually 48kHz.

  • Sampling: waveform amplitude on the analog signal is continuous sample value, in the digital signal, the signal is usually discontinuous, so the analog signals after quantification, takes only an approximation of integer values, in order to record the amplitude values, the sampler can adopt a fixed number of bits to record the amplitude value, usually eight, 16 and 32 bit. The more bits, the more accurate the recorded value, the higher the restore degree.

  • Channel number: The number of sounds that can support different sounds.

  • Bit rate: Bit rate, the amount of information per second (BPS) that can pass through a data stream. Audio bit rate = sampling rate * Sampling bits * Number of channels

video

  • Resolution: The number of horizontal and vertical pixels, indicating the degree of fineness of the image. The P of 1080P refers to Progressive scan, or vertical pixel point, which is “high”, so 1920 * 1080 is called 1080P, not 1920P.

  • Bit rate: Concept and audio bit rate.

  • Frame rate: The number of frames per second or frames per second.

  • RGB: red, green and blue. All colors can be mixed with R, G, and B base colors.

  • YUV: A color format in which brightness and chroma are separated.

    • Y: Brightness is the gray level. In addition to the brightness signal, it also contains more green channels.
    • U: difference between blue channel and brightness;
    • V: the difference between the red channel and brightness.

Because the human eye is sensitive to brightness, not sensitive to chroma, so reduce part of the AMOUNT of UV data, the human eye is unable to perceive, so you can compress the RESOLUTION of UV, without affecting the perception of the premise, reduce the volume of the video.

  • RGB and YUV conversion:

    R Y = 0.299 + 0.114 + 0.587 G B U R = 0.147 0.289 G + 0.436 = 0.615 B V R - 0.515 G - 0.100 B -- -- -- -- -- -- -- -- -- R = Y + 1.14 V G = Y -0.39U -0.58V B = Y + 2.03uCopy the code