WiFi Display 那些事兒一
@(WiFi)[Display,架構,應用場景]
還是用MarkDown寫東西舒爽,公司的KB排版還是太亂了
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- WiFi Display 那些事兒一
- 基本概念
- 特點
- 協定架構
- 認證要求
- Program 要求
- 支援的音視訊資料格式
- Source Sink 工作網絡拓撲
- WiFi Display 常見使用場景總結
- Scope of Work 原理架構
基本概念
a. 蘋果的AirPlay ,将iPhone、iPad及Mac 的視訊鏡像通過無線(WiFi)傳送到AirPlay的裝置上。 還可以支援Apple TV的雙屏遊戲體驗
b. DNLA(Digital Living Network Alliance)技術 , 為索尼、Intel、微軟等聯盟一起組織定義出來 一套協定(該協定支援在PC、移動裝置、消費電器互聯互通) , DNLA與AirPlayl類似,但沒有類似Apple Tv 的AirPlay功能, 更多的是将移動端的照片與視訊傳送到大螢幕中(Source端)。
c. Miracast , 由 WiFi聯盟12年所定制,以WiFi直連作為無線顯示的标準。 支援此标準的裝置,可通過 WiFi(無線)方式分享視訊畫面。與DNLA不同,Miracast類似于AirPlay鏡像功能,可實作移動端與高清電視多屏互動。此外,Miracast為WiFi聯盟對支援WiFi Display功能裝置認證名稱。
特點
a. 裝置連結獨立性,無需借助外部網絡或者路由器
b. 在現有的WiFi協定下,易于發現與連結裝置以及建立會話、加密
協定架構
Source – A device that is capable of transmitting multimedia content
Sink — A device that is capable of receiving and rendering multimedia content
一般的移動裝置端作為Source端,它與Sink端的差異在于前者為發送,後者為接收
Session – A WiFi Display connection between Source and Sink Device
TLDS — Tunneled Direct Link Setup
前者: 可粗略的了解為連結的基本單元,用承載傳輸的内容(内容源産生于Source Device , 被接收&抽象解析出來于Sink Device)
後者: 基于802.11無線協定的直線連結,一般指的為STAs(client devices)與Ap(Service)之間直連
認證要求
- WiFi Miracast : 基于WiFi Display 協定規範
- Connectivity : WiFi Certified n
- Device-to-Device connectivity : WiFi Direct + TDLS(optional)
- Security : WPA2
- Quality of sevices :(QoS)
- Battery life : WMM Power Save //節能控制
- Ease of installation : WiFi Protected Setup
Program 要求
- a. Mirror a wired setup between a Source and Sink //這裡的wired == point to point (建立起來的類似“有線”連結)
1: Establish a point-to-point connection between Source and Sink
2: End-user Wi-Fi Display experience should mirror the wired experience in all ease of use, device discovery and quality of the rendered content
// 簡單總結為: 終端裝置需要支援這些功能(discovery 、 decode 收到的視音頻資料)
- b. Key components of Wi-Fi Display
1: Enable and sustain connection
2: Easy to setup and configure, straight forward to discover
3: Provide at a minimum, the security of a typical Wi-Fi CERTIFIED™ link between the Source and Sink
4: Provide a mechanism so the Source and Sink can select the best operating channel // 這一部分要求較高
支援的音視訊資料格式
a. H.264 codecb. 顯示分辨率Three H.264 Profiles supported, with level range of 3.1 - 4.2 for each
• CBP (Constrained Base Profile
• CHP (Constrained High Profile)
• Chi444P (Constrained High 444 Profile)
Minimum required support is CBP at level 3.1
c. Audio Codecs– 17 CEA (Consumer Electronic Association) formats
• 640 x 480p up to 1920 x 1080p
• Frame rates from 24 frames per second (fps) to 60 fps
– 30 VESA formats
• 800 x 600p up tp 1920 x 1200p •
Frame rates at 30 and 60 fps
– 8 handheld formats
• 640 x 360p up to 854 x 480o
• Frame rates at 30 and 60 fps
– Minimum required support is 640 x 480p at 60 fps
– 23 LPCM modes
• 44.1/48/96/192 KHz; 16/20/24-bit, 2-8 channels
– 4 AAC modes
– 7 E-AC3 (Dolby Digital) modes
– 3 DTS modes
• The only mandatory codec is LPCM16-48-2
• 48 kHZ sampling, 16 bits, 2 channels
Source / Sink 工作網絡拓撲
a. Source –> Sinkb. Source (with access to AP) –> Sink
- A Source devices streams its local content to the Sink device
A Source devices streams its local content (or internet content via connecte WLAN) to the Sinkc. Source (not connect AP) –> Sink與a 類似(Source 将本地的内容傳輸到Sink)d. Source to Sink (Both are connected via WlAN AP to the Internet )A Source devices streams its local(internet) content to the Sink Device
WiFi Display 常見使用場景總結
Scope of Work (原理架構)
- 如下圖,AV(Audio/Video)資料從Source —> Sink (是基于WiFi Interface (這一部分主要在WPA_SUPPLICANT 中的 p2p實作,這一部分将會放在後面講解))
- 一些常見功能(支援或可選)