The document summarizes key aspects of the WiFi Display standard for wirelessly streaming audio and video content between devices. It describes the protocol methods, architectural view, supported media types, encapsulation of media in transport packets, and parameters for compression, frame skipping, and error recovery. The standard uses UDP and RTP to transport encoded H264 video, audio in various formats, and associated metadata in MPEG-2 transport stream packets between devices for wireless display functionality.
5. Media
The Media Types supported by WFD:
H264
MPEG2 AAC
Dolby AC3
LPCM (uncompressed audio)
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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
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8. Media Transport Stack
Encoded audio/video streams are carried in MPEG2 Transport stream
The MP2TS packets are carried in RTP packets
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9. H264 Profiles
WFD supports two H264 profiles:
Constraint Base Profile
Base profile without FMO, ASO
Constraint High Profile
High profile without CABAC, 4x4
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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
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11. PMT Table
Media Type PMT Media Type
H.264 0x1B
LPCM 0X83
AC3 0X81
AAC 0X0F
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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
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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
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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
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