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WiFi Display

WiFi Display



Introduction to WiFi Display video coding and architecture

Introduction to WiFi Display video coding and architecture



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    WiFi Display WiFi Display Presentation Transcript

    • WiFi DisplayStandard 1
    • Protocol Methods Proprietary  Over TCP (what’s inside?) Standard WFD  Over UDP, WFD Header, MP2TS packets with 2
    • 3
    • Architectural view 4
    • Media The Media Types supported by WFD:  H264  MPEG2 AAC  Dolby AC3  LPCM (uncompressed audio) 5
    • MP2TS packetization in WFD WFD carries media (H264, AAC) in MP2TS packets 7 MP2TS are carried in a single RTP packet RTP TS is derived from MP2TS and sent according to WLAN sync 6
    • Media Encapsulation Encapsulation of H264V into NAL/PES/MP2TS/RTP 7
    • Media Transport Stack Encoded audio/video streams are carried in MPEG2 Transport stream The MP2TS packets are carried in RTP packets 8
    • H264 Profiles WFD supports two H264 profiles: Constraint Base Profile  Base profile without FMO, ASO Constraint High Profile  High profile without CABAC, 4x4 9
    • PAT & PMT PAT Should indicate PMT PID 0x100 PMT Should indicate PCR PID at 0x1000 PMT Should indicate video PID at 0x1011 PMT Should indicate Audio PID at 0x1100 (additional audio streams PID are consecutive) The above tables (PCR,PAT/PMT…)should be sent at intervals smaller than 100mS 10
    • PMT Table Media Type PMT Media Type H.264 0x1B LPCM 0X83 AC3 0X81 AAC 0X0F 11
    • Compression parameters changes Parameter compression change can follow changes in:  Device usage (Game, Video)  Power (low battery)  WLAN bandwidth changes When changing compression parameters Source could:  Change parameters without announcement  Declare parameter changes using M4 RTSP request message 12
    • Frame Skipping WFD Frame skipping refers to removal of ALREADY encoded video frames Skipping is done AFTER the encoder Frame number in slice header are sequential even when frames are skipped -> requires stream changing after encoder The maximum skip interval is defined in bits B1:B3 of the wfd-video-formats parameters in M3 response Frame skipping allowed only on non-referenced streams ->Skipping complete GOPs Not recommended 13
    • Frame Refresh / Recovery In case of video streams errors (duo to packet loss), the decoder may detect those errors The Sink may decide that the errors are request a frame refresh (IDR Frame) Request is done using the SET_PARAMETERS message with wfd_idr_request param 14