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Wireless PC2TV
The document outlines a project for a low-cost wireless solution to link a laptop to a television, emphasizing applications such as home use and presentations. It details specifications, video compression methods, and streaming performance and highlights the use of various protocols and hardware for efficient connectivity. Additionally, it includes information about network automation and benchmarking against competitor products.
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Wireless PC2TV
- 1. Low cost wirelesslaptop link to TV Anish Sane Deepak Malani Guided by : TVP, NVCR Sponsored by: Philips
- 2. User Scenario • Aim- Display laptop screen contents onto Television, with wireless connectivity • Applications – Home use (one source, one destination) – Conference room with Digital projector (n sources, one destination) – Multicast streaming at gatherings (one source, n destinations)
- 3. Target Specifications Features Specifications Video resolution 1280x720 Frames per second 30 Colour Resolution 24-bit True Colour Video Interfaces Digital: DVI OS on Laptop Linux OS on Board Linux Distance between Laptop & TV 10m (30ft) Power Supply 5V Adapter
- 4. System Overview Television Video Memory DVI Encoder IC Grabbing Decoding Streaming USB Port USB Wi-Fi dongle USB Wi-Fi dongle Beagle Board Laptop Side (Tx) TV Side (Rx)
- 5. Part I Content Generation(Laptop side) Content Display (TV side)
- 6. Video data rate •Video frame grabbing • Raw data rate (1280x720) x 30 fps x 24bits/frame = 663.5 Mb/s • Throughput offered by 802.11g devices = 22Mbps • Hence necessity for video compression – Compression ratio (>30)
- 7. 1. Content Generation •Initial Approach – Framebuffer (/dev/fb) – Grab RGB pixel data – RGB to YUV transcode with 4:2:0 subsampling – YUV to MPEG-2 stream using libavcodec (open- source) • Performance – 640x480@3fps • Evaluation – Device file read takes 200ms/frame
- 8. Video display mechanism(Laptop) Video Grabbing Application Frame Buffer /dev/fb Graphics Display XShared Application Memory Display hardware No Hardware Graphics Video Display Acceleration Application Adapter Required ? Yes
- 9. Content Generation • Approach2: – Grab from Xshared Memory (XShm) • APIs from open source – XShmGetImage() • Performance – 1280x720@30fps – MPEG-2 compression using ffmpeg (based on libavcodec)
- 10. Compression schemes MPEG-2 MPEG-4 H.264 (MPEG-4/AVC) Compression Ratio x 1.2x 2x Computation Time y 1-1.4y 4y-6y (for various video bit-rates) • Compression Ratio x = 60-300 • Computation time (PC) for encoding y = 1 second for 2.6 seconds of video
- 11. Bottleneck Diagram PC/Laptop TV side side 11Mbps 6Mbps 2 Mbps 5.5 Mbps Content Generation Content Streaming Content Displaying HD Quality HD720p HD, 1280x720 1280x720@30fps framedrop if > 2 Mbps
- 12. Generated Data Rate(after compression) • DCT Quantization scale v/s bitrate 12000 11036 (2) 10000 8000 Bitrate (kbps) 6000 5531.6 (4) 4000 3139.5 (8) 2000 2100.3 (14) 984.7 (31) 0 0 5 10 15 20 25 30 35 Qscale (2-31)
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- 15. 2. Content Decodingon TV side • BeagleBoard • Processor – OMAP3530 – 600MHz ARM Cortex core – NEON SIMD Coprocessor (advantageous for video applications) – C64x+ DSP • Interfaces – USB for Wifi device – Digital Video Interface (DVI) for TV – SDIO for filesystem and storage
- 16. Software on Board •2.6.28 kernel • Video Decoder • Mplayer – Uses libavcodec – Uses NEON acceleration
- 17. DSP Acceleration • Gstreamermultimedia framework which uses DSP/BIOS Link • Pipeline based application – filesrc | demux | codec | sink • Codec – ffdec_mpeg2video – TI evaluation codecs – No HD codecs for 720p yet for DSP
- 18. Video Decode Performanceon Board • Resolution: 1280x720 • Frame rate: 24 (streaming videos) 30 (captured videos) • Video fidelity: 2 Mbps – At higher bit rates, frame rate decreases • Comparison of video fidelity (pictures) • Power consumption=2W (0.4amp, 5VDC)
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- 21. System Overview XSharedMemory Television Grab continuously DVI Encoder IC Transcoding framebuffer software to stitch Grabbing Decoding into raw video Mpeg decode with Compression DSP Accerlation software using ffmpeg video codec Streaming libraries compressed_video.mpeg Buffer memory USB Port USB Wi-Fi dongle USB Wi-Fi dongle Beagle Board Laptop Side (Tx) TV Side (Rx)
- 22. Part II Content Streaming and Automation
- 23. Objectives • Wireless connectivity between laptop and TV • Automatic detection and pairing of two devices • Selectivity among multiple streams
- 24. Wireless Solutions • 802.11g Netgear WG111GE (Realtek) • Super-G TP-link (Atheros) • 802.11n Star-king (Atheros) • D-link DWA110 (Ralink)
- 25. Wireless Connectivity • Wi-FiDongle (802.11g) D-link DWA110 (rt73 based): – Driver support : kernel.org • rt73usb – Modes supported: infrastructure(managed), ad- hoc, monitor – We are using ad-hoc mode for point-to-point communication – Data rate: 5Mbps-16Mbps (More data rate when better S/N ratio)
- 26. Ad-hoc mode • Forpoint-to-point connection, no necessity of having an access point • No time/bandwidth overhead for data going via an AP (as in infrastructure mode) • No consumption of bandwidth due to beacons from AP • The laptop and the board can use channels with mutual understanding & independent of AP's channel
- 27. Alternate to Ad-hocmode • Using one side in managed mode & attaching an AP on other (over wired link) • Was thought to be useful when the dongles/driver do not support ad-hoc mode – Netgear WG111GE (RTL8187B) • Gives about same speed as ad-hoc
- 28. Protocol used • TCP: – Error control & retransmission on error • UDP: – Assumes error control at the application layer – No implicit retransmission at protocol level
- 29. Protocol used • Weare using HTTP+TCP • Packet drops are severe when UDP is used (over Wi-Fi) • Motion vector errors • Retransmission can increase the lag between captured & played video • Data rate requirement can be satisfied, even with retransmission • Over wired link UDP packet drops are not so significant
- 30. Bottleneck Diagram PC/Laptop TV side side 11Mbps 6Mbps 2 Mbps 5.5 Mbps Content Generation Content Streaming Content Displaying HD Quality HD720p HD, 1280x720 1280x720@30fps framedrop if > 2 Mbps
- 31. Automation - Networking CreateNetwork on Laptop Board Boots up Start DHCP Server on board Search For network No Yes Laptop asks for IP, Board provides IP mode,essid,cell Network Found? match? No Yes Verify connectionNo Connect to the network (mode,essid,cell) Connection Established
- 32. Automation – Streaming •Laptop side Streaming server Grabbing application (ffmpeg) • Board side – Streaming client – Media Player (mplayer or gstreamer) • Data transfer between applications – This is done using named pipes i.e. FIFOs
- 33. User interface • Reconnect – If the network gets disconnected, the user can use this button to reconnect • Select Stream – When there are multiple sources, this control can be used to switch between them • Reset – If the device freezes completely
- 34. Demo Plan • Real-timescreen capture on laptop and stream to television, over Wi-Fi • Video file streaming from laptop to TV on Wi- Fi • Resolution: 1280x720
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- 36. User-space & kernelspace switching
- 37. Gstreamer framework (usingDSP/BIOS Link)
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- 39. Screen Capture With andwithout acceleration
- 40. Product Comparison Features Our Product Hauppauge Addlogix InternetVue Resolution 1280x720 720x576 1024x768 (graphics) (video) 640x480 (video) Video Ports DVI/HDMI S-video, DVI, VGA C-video File Support Any type Limited to MPEG, Any type JPEG, MP3, DivX Screen Capture Yes No Yes Mode Cost $150 (BOM) $149 $229 Wireless 802.11b/g/n 802.11g 802.11g Connectivity Ethernet Yes Yes Yes Connectivity