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WiFi Display


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Introduction to WiFi Display video coding and architecture

WiFi Display

  1. 1. WiFi DisplayStandard 1
  2. 2. Protocol Methods Proprietary  Over TCP (what’s inside?) Standard WFD  Over UDP, WFD Header, MP2TS packets with 2
  3. 3. 3
  4. 4. Architectural view 4
  5. 5. Media The Media Types supported by WFD:  H264  MPEG2 AAC  Dolby AC3  LPCM (uncompressed audio) 5
  6. 6. 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
  7. 7. Media Encapsulation Encapsulation of H264V into NAL/PES/MP2TS/RTP 7
  8. 8. Media Transport Stack Encoded audio/video streams are carried in MPEG2 Transport stream The MP2TS packets are carried in RTP packets 8
  9. 9. H264 Profiles WFD supports two H264 profiles: Constraint Base Profile  Base profile without FMO, ASO Constraint High Profile  High profile without CABAC, 4x4 9
  10. 10. 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
  11. 11. PMT Table Media Type PMT Media Type H.264 0x1B LPCM 0X83 AC3 0X81 AAC 0X0F 11
  12. 12. 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
  13. 13. 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
  14. 14. 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