What is Miracast Screen Projection Protocol? In-depth analysis of Miracast Screen Projection protocol

Miracast is developed by the WiFi Alliance and uses Wifi-Direct and IEEE802.11 as wireless transmission standards to enable mobile phones to wirelessly transmit videos and pictures to televisions or other receiving devices. Miracast and Miracast similar screen projection protocols, Airplay, DLNA, chromecast, etc., are mainly analyzed in today’s Miracast protocol.

Miracast performs device discovery based on WiFi P2P, or TDLS, or Infrastructure, located in the data link layer of the OSI model. The media transmission control uses the RTSP protocol, as well as remote I2C data reading and writing, UIBC user input reverse channel, HDCP high bandwidth content protection, etc., located in the OSI model of TCP/IP transmission control layer and network layer. Among them, the audio and video data is encapsulated into PES packets, protected by HDCP content, then encapsulated into TS packets, and then encapsulated into RTP packets, which are sent using RTSP protocol.

Device discovery
Miracast supports three device discovery modes: WiFi-P2P, TDLS, and Infrastructure.

  1. WiFi-P2P
    P2P is a point-to-point connection, which is based on Wifi-direct to realize WiFi Direct connection without passing through wireless hot spots.
  2. TDLS
    TDLS, full name of Tunneled Direct Link Setup, are established in direct connection of tunnels, which are connected through Access Point (AP) or Group Owner (GO).
  3. Infrastructure
    Infrastructure realizes device discovery service through multicast through AP wireless hotspot.

Audio and video support formats

1, audio support format

Audio support formats include: LPCM, AAC-LC, AC-3, E-AC-3, Dolby TrueHD, AC-4, MPEG-4 AAC, MPEG-H 3D Audio, etc. Among them, the sampling rate, sampling number and number of channels are limited.

  1. Video support format

The supported video formats include H264 and HEVC. H264 profiles support CBP(Constraint Baseline Profile) and Restrict High Profile (RHP). By comparing CBP and RHP, it can be seen that CBP only supports I-frame and P-frame, CAVLC, YUV420P, etc.