“🌟🌟🌟🌟🌟“

“Taste: Crispy meat with salt and pepper“

“Cooking time: 10min“

Github github.com/Geekhyt, welcome to the canteen, if you think the food is delicious, a Star is a great encouragement to the canteen owner.

Bit rate (Bit rate, Bit stream)

Represents the number of bits transmitted per second.

Bit rate is also known as “binary bit rate”, commonly known as “bit rate”, “bit stream”, also known as data signal rate. This big brother has many aliases.

Moore’s law applies not only to transistor density, but also to transmission speed: bit rates double roughly every 18 months.

unit

Bit /s (bit/s or BPS), kbit/s (kbit/s or KBPS), Mbit/s or Mbps

(1Mbps = 1000kbit/s)

The higher the bit rate, the more data is transferred per unit of time.

The formula

Bit rate (KBPS) = File size (KB) x 8 / time (s)

For example, if the capacity of the video file is 2.888 gb and the length of the video is 100 minutes (6000 seconds), the bit rate is approximately 4037kbps (2.888 * 1024 * 1024 * 8/6000 = 4037.717).

The Frame rate of Frame rate

How many times per second can the graphics processor refresh, which is how many frames can be played per second.

The special biology of the human eye considers images to be coherent at a frame rate higher than about 10 to 12 frames per second, known as visual persistence.

Low frame rates can cause visual stutter, and the higher the frame rate, the higher the fluency.

If you’ve ever played LOL, keep the game frame number around 60 or above and your graphics are smooth.

unit

The number of Frames per Second (FPS) or Hertz (Hz) displayed.

Compression rate Compression rate

Compressed file size/original file size x 100% = Compression ratio

The compression rate is generally the smaller the better, but the smaller the pressure, the longer the decompression time.

Image resolution

Commonly referred to as PPI, a parameter used to measure the amount of data in an image.

The higher the pixel density, the denser the pixels, 5 ppi means 5 pixels per inch and 500 ppi means 500 pixels per inch.

Higher PPI numbers mean higher resolution for pictures and videos.

The formula

Resolution = number of pixels per unit length/unit length

unit

DPI (dots Per inch), LPI (lines Per inch), PPI (pixels Per inch) and PPD (pixels Per Degree).

PPD, not PDD.


The container format

MP4

It was developed by the Moving Picture Experts Group (MPEG) under the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC).

MP4 is very open and can be used to describe almost any media structure. Supports streaming media, is widely used for H.264/H.265 video and ACC audio, is the carrier of HD video.

AVI

AVI (Audio Video Interleaved) is Microsoft’s answer to Apple’s QuickTime. It can be used across multiple platforms, but is bulky and compression standards are inconsistent.

FLV

Flash Video (FLV) is the most popular streaming media format. It has a small file size and is easy to encapsulate and play. It is suitable for network applications. Most major video sites will use FLV format.

TS,M3U8

HLS consists of TS and M3U8:

  • . M3u8 file: an M3U file encoded in UTF-8.
  • . Ts video files: One M3U8 file corresponds to several TS files.

M3u8 only stores some configuration information and related paths of TS files, while TS files store video data. When the video is played, the video tag will parse the M3U8 and find the corresponding TS file to play.

However, the delay of HLS is relatively high, including TCP handshake, M3U8 file download and parsing, TS file download and parsing and other steps. While you can shorten the length of the list and limit the size of a single TS file to reduce latency, you can increase the number of requests and strain the server.

Apple’s official recommended TS duration is 10s, with a delay of about 30s.

WebM

WebM, proposed by Google, is an open, royalty-free media file format designed for the Web. WebM files contain video streams compressed using VP8 or VP9 video codecs and audio streams compressed using Vorbis or Opus audio codecs.

OGV

OGV is a video format in HTML5 called Ogg Theora, derived from the Ogg container format (open-source by Xiph.Org), which is not limited by software patents.

MOV

MOV is a common QuickTime movie format with excellent compatibility for Both Macintosh and Windows.

Coding format


H.264 (AVC)

H.264 is a video compression technology or codec (such as MPEG-4 Part 10, Advanced Video Coding or AVC) jointly developed by the International Telecommunication Union and the INTERNATIONAL Organization for Standardization/INTERNATIONAL Electrotechnical Commission Moving Image Expert Group. It is based on MPEG-4 technology. Widely used in network streaming media data, network software, high definition TV, satellite and so on.

H.265(HEVC)

Used to replace the H.264/AVC coding standard. The same video file encoded using H.265 is about 1/3 of the size of mPEG-4.

  • Support 4K and higher resolution, good user experience
  • High compression can provide users with more content, lower costs, and increase download speeds
  • Poor browser support, industry solutions: libe265.js, FFMpeg + WebAssembly

VP9

VP9 is a free and open source image encoding format developed by Google to replace VP8 and compete with H.265/HEVC. More than 2 billion endpoints support VP9 decoding, including Chrome, Opera, Edge, Firefox and Android devices and millions of smart TVS.

The technology for encoding VP10 video is included in the AV1 code led by the Open Media Alliance, so Google says it will not be deploying or officially releasing VP10 internally.

AV1

AV1 (Alliance for Open Media Video 1) is an Open source, copyright free Video encoding format developed by AOM (Alliance for Open Media), specially designed for streaming over the network. The IETF has also standardized this work into the Internet video codec (NetVC).

AV1 aims to solve h.265’s costly patent fees and complex licensing issues and become the next leading royalty free coding standard. It is the successor to Google’s VP9 standard and a strong competitor to H.265.

  • YouTube has begun experimenting with AV1 video formats for some of its videos.
  • On February 5, 2020, Netflix began to play movies on Android devices using AV1 video format with a limited compression efficiency of 20% over the original VP9
  • On April 30, 2020, IQiyi announced support for AV1 video format on PC Web browsers and Android devices.

reference

  • WebM
  • VP9
  • AOMedia Video 1
  • H.264/MPEG-4 AVC
  • Amoy technology multimedia front end manual

❤️ Love triple punch

1. Please give me a “like” when you see this. Your “like” is the motivation for my creation.

2. Pay attention to the front canteen of the public account, “your front canteen, remember to eat on time”!

3. This article has been included in the front canteen Github github.com/Geekhyt, for a small Star, thanks to Star.