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DV/HDV Tape Drive Synchronization

DV/HDV Tape Drive Synchronization. Stereoscopic Displays and Applications Conference 29 th – 31 th January 2007 San Jose, United States. Overview. Introduction to the Stereoscopic Multiplexer Concept and architecture DirectShow capture graphs Simple tape drive synchronization Basic idea

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DV/HDV Tape Drive Synchronization

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  1. DV/HDV Tape Drive Synchronization Stereoscopic Displays and Applications Conference 29th – 31th January 2007 San Jose, United States

  2. Overview • Introduction to the Stereoscopic Multiplexer • Concept and architecture • DirectShow capture graphs • Simple tape drive synchronization • Basic idea • Missync detection • Advanced tape synchronization concepts • Buffering data in system memory • Recognizing invalid scenes Peter Wimmer - 3dtv.at

  3. Stereoscopic Multiplexer Concept R L R L Right stream Left stream Combined video stream Peter Wimmer - 3dtv.at

  4. DirectShow • DirectShow • Architecture to process media data on the Windows platform • Processing objects are called filters • Filters expose input and output pins • Filter pins can be connected to a directed graph • Each capture device is represented by a capture filter • Stereoscopic Multiplexer • Not a proprietary capture applications but … • … implemented as DirectShow capture filter • Can be used from any capture application Peter Wimmer - 3dtv.at

  5. DirectShow Capture Graph • The capture application loads… • … the capture device filter • … the downstream filters • Example downstream filters are • … video renderers • … file writer • … network renderer Capture Device Sink Peter Wimmer - 3dtv.at

  6. Stereoscopic Multiplexer Capture Graph 3dtv.at Stereoscopic Multiplexer Sink Left Capture Device Right Capture Device • The application loads… • … the Stereoscopic Multiplexer • … the downstream filters • The Stereoscopic Multiplexer loads… • … the ‘real’ physical capture drivers • … video decoders (if required) Peter Wimmer - 3dtv.at

  7. Stereoscopic Multiplexer Architecture Application Application DirectShow- Filter Stereoscopic Multiplexer User Mode WDM Video Capture Filter WDM Video Capture Filter WDM Video Capture Filter Miniport Driver MiniportDriver Miniport Driver Kernel Mode Peter Wimmer - 3dtv.at

  8. Two camcorders + remote control Full resolution Optimum image quality No immediate playback possible One camcorder + optical attachment Half resolution per eye Degraded image quality Simple playback Stereoscopic Video Recording Peter Wimmer - 3dtv.at

  9. Dual Tape Playback • Problem • Different number of frames on the tapes • Usually happens when camcorders were turned off • Playing back dual camcorder recordings • Starting both tapes simultaneously  tapes drift apart • Transfer both tapes to harddisk  splitting scenes playing each scene separately  ok but inconvenient Peter Wimmer - 3dtv.at

  10. Tape Synchronization • Tape synchronization involves… • … detecting missync • … correcting missync • Detecting missync • Image analysis: tracking motion and parallax not reliable, computationally complex • Sound analysis: detecting corresponding events in the left and right audio track does not work for silent scenes • Scene change detection: based on metadata (recording date and time) in the compressed DV stream reliable, no computational overhead Peter Wimmer - 3dtv.at

  11. Basic Tape Synchronization • Resynchronize • Pause first tape • Wait for scene changeon second tape • Pause second tape • Step forward tosmallest common offset from the scene changes • Send ‘play’ commandto both tapes • A tolerance of one frame is good tradeoff between playback interruptionsand sync quality Wait for scene change Yes Scene change occurs on the other tape within a certain tolerance? No Resynchronize Peter Wimmer - 3dtv.at

  12. Basic Tape Synchronization Graph Tape control Timecode Recording date/time, timecode Microsoft DV Camera and VCR 3dtv.at Metadata Reader DV Video Decoder 3dtv.at Stereoscopic Multiplexer Sink Microsoft DV Camera and VCR 3dtv.at Metadata Reader DV Video Decoder Created by Stereoscopic Multiplexer Peter Wimmer - 3dtv.at

  13. Tape Synchronization Graph with Audio • Audio data are sent to sound card • Audio data are not available for capturing 3dtv.at Audio Slaving Filter Audio Renderer Media type: A/V interleaved Microsoft DV Camera and VCR 3dtv.at Metadata Reader DV Splitter DV Video Decoder 3dtv.at Stereoscopic Multiplexer Media type: Video only Microsoft DV Camera and VCR 3dtv.at Metadata Reader DV Video Decoder Peter Wimmer - 3dtv.at

  14. HDV Support • HDV standards • HDV1: 720p (1280 x 720 pixels), used by JVC • HDV2: 1080i (1440 x 1080 pixels), used by Sony and Canon • MPEG-2 interframe compression • Downconversion mode • Standard definition playback  low system requirements • Firewire output of camcorders set to DV mode • Camcorders perform downconversion from HDV to DV • DV graphs still work • Native HDV mode • High definition playback  high system requirements • Metadata readers parse MPEG streams • Changes to the filter graph are necessary Peter Wimmer - 3dtv.at

  15. HDV Graph MPEG Audio Decoder 3dtv.at Audio Slaving Filter Audio Renderer Audio stream • MPEG transport stream • PID 0810h: Elementary video stream • PID 0814h: Elementary audio stream • PID 0811h: Video auxiliary stream (contains metadata) Microsoft AVC Tape Subunit Device MPEG-2 Demultiplexer 3dtv.at Metadata Reader MPEG-2 Video Decoder Video stream Video aux stream 3dtv.at Stereoscopic Multiplexer 3dtv.at Metadata Reader MPEG-2 Video Decoder Microsoft AVC Tape Subunit Device MPEG-2 Demultiplexer Peter Wimmer - 3dtv.at

  16. Advanced Tape Synchronization • Problems with basic tape synchronization • Frequent playback interruptions • Frames are multiplexed in the order they arrive • Precision only approx. ±1 frame • Solution • Synchronize the multiplexer output, not the camcorders • Buffer data in system memory to delay the stream that is ahead • Resynchronize tapes only if buffer is full • Precise synchronization based on offset from scene change • Invalid scene recognition • Detect scenes that are present just on one of the tapes • Pause the other tape until matching scenes have been found • Implementation: Monitor difference of left and right recording date/time • Clock time might not be set accurately  do not monitor absolute time Peter Wimmer - 3dtv.at

  17. Invalid Scene Recognition • Do not drop the first scene after startup • Do not drop the first scene after a recording break (it is likely that the clocks have been adjusted or another pair of camcorders was used) Peter Wimmer - 3dtv.at

  18. Advanced Tape Synchronization Graph • Media sample buffers operate on compressed streams • Buffering one second DV/HDV video requires 3.5 MB of memory 3dtv.at Audio Slaving Filter Audio Renderer Microsoft DV Camera and VCR 3dtv.at Media Sample Buffer 3dtv.at Metadata Reader DV Splitter DV Video Decoder 3dtv.at Stereoscopic Multiplexer DV Video Decoder Microsoft DV Camera and VCR 3dtv.at Media Sample Buffer 3dtv.at Metadata Reader Peter Wimmer - 3dtv.at

  19. Version 0.5 (May 2006) Basic DV tape synchronization Configuration tool Version 0.6 (Q1 2007) Advanced DV/HDV tape synchronization HDV support (HDV2 only) Stereoscopic Multiplexer Versions Peter Wimmer - 3dtv.at

  20. Q&A Thanks for Your Attention Visit us at http://www.3dtv.at! Peter Wimmer - 3dtv.at

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