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Versions: 00 01 draft-ietf-mmusic-parallax-attribute

mmusic                                                   B. Greevenbosch
Internet-Draft                                                    Y. Hui
Intended status: Standards Track                     Huawei Technologies
Expires: November 20, 2011                                  May 19, 2011


                    SDP attribute to signal parallax
            draft-greevenbosch-mmusic-parallax-attribute-01

Abstract

   This document introduces a "ParallaxInfo" attribute in SDP.  This
   attribute can be used in stereoscopic applications, to signal the
   depth positioning of 2D media data within the 3D space.





































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Note

   Discussion and suggestions for improvement are requested, and should
   be sent to mmusic@ietf.org.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on November 20, 2011.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.















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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  5
   3.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  The ParallaxInfo attribute . . . . . . . . . . . . . . . . . .  7
   5.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   6.  Remarks  . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   9.  Normative References . . . . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15







































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1.  Introduction

   To see a 3D scene, the human brain interprets two different views as
   perceived by the left and right eyes, and fuses these views into a
   single 3D perception.  The depth of the object is perceived by
   interpreting the horizontal shift of that object between the views.
   This shift is called "parallax".

   In stereoscopic 3D multimedia applications, there are various ways to
   transmit media streams in 3D. One way is to transmit two different
   streams, one for the left eye and one for the right eye.  These
   streams are then projected to the relevant eyes using the appropriate
   technology.

   When sending text streams in 3D, the solution mentioned above would
   imply sending the same text stream twice.  Since the two streams
   would only differ in horizontal positioning, this introduces a lot of
   unnecessary overhead.

   This document specifies a "ParallaxInfo" attribute in SDP [RFC4566],
   which is used to transfer the parallax information.  It eliminates
   the need to send two different streams separately, as they can be
   calculated from a single stream and the "ParallaxInfo" attribute
   value.

   The attribute transfers this information as two parameters: one
   indicating which view (left/right/centre) is carried by the stream,
   and another to signal the parallax between the objects.

   The attribute is not restricted for signalling the parallax of text
   streams, but it can also be used to place other 2D objects in the 3D
   space.  Examples include a channel logo, an electronic programme
   guide and on-screen display of an audio volume indicator.


















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2.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].














































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3.  Definitions

   L-view
      A visual entity that is to be projected to the left eye.  In the
      case of video, the L-view is a video frame designated for the left
      eye.  In the case of text, the L-view is the text positioned for
      viewing by the left eye.

   L-stream
      A sequence of L-views, which is streamed to the device.

   R-view
      A visual entity that is to be projected to the right eye.  In the
      case of video, the R-view is a video frame designated for the
      right eye.  In the case of text, the R-view is the text positioned
      for viewing by the right eye.

   R-stream
      A sequence of R-views, which is streamed to the device.

   C-view
      The centre view: a visual entity as seen from a viewpoint between
      the left and right eyes.  The C-view can be used to calculate the
      L- and R-views.

   C-stream
      A sequence of C-views, which is streamed to the device.

   stereoscopic device
      A device that is able to produce and display different images for
      the left and right eyes, such that the viewer can experience a 3D
      view.

   2D device
      A device that is not able to produce and display different images
      for the left and right eyes.

   2D media stream
      A sequence of two dimensional visual entities (such as text or 2D
      graphics), which is streamed to the device.











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4.  The ParallaxInfo attribute

   The SDP attribute "ParallaxInfo" is used to transmit the depth
   positioning of 2D media data, such as a text stream, in the 3D space.

   The attribute has the following syntax:

      a=ParallaxInfo:<transmitted position> <parallax>

   The <transmitted position> indicates whether the L-, C- or R-stream
   is transmitted, whereas <parallax> indicates the parallax (i.e.
   shift) between corresponding L- and R-views in pixels, normalised to
   a screen width of 11520 pixels.  To convert the value of <parallax>
   to match the display video screen width W, it has to be divided by a
   factor F=11520/W.

   The <transmitted position> can have the following values:

   "L"  indicates that the transmitted stream is the L-stream.  A
      stereoscopic device MUST calculate the corresponding R-views by
      shifting the L-views <parallax>/F pixels towards the right.

   "C"  indicates that the transmitted stream is the C-stream.  A
      stereoscopic device MUST calculate the corresponding L-views by
      shifting the C-views <parallax>/(2*F) pixels towards the left, and
      the R-views by shifting the C-views <parallax>/(2*F) pixels
      towards the right. <parallax> SHOULD be even.  If it is odd, the
      divided value MUST be rounded off towards zero.

   "R"  indicates that the transmitted stream is the R-stream.  A
      stereoscopic device MUST calculate the corresponding L-views by
      shifting the R-views <parallax>/F pixels towards the left.

   <parallax> MAY be negative.  In this case, the shift direction is
   reversed.

   The "ParallaxInfo" attribute can be a session-level attribute or a
   media-level attribute.  As a session-level attribute, it specifies
   the default parallax value which can be applied to all the 2D media
   streams in the session being described.  As a media-level attribute,
   it specifies the parallax value which can be applied to the
   associated 2D media stream, overriding any session-level parallax
   value specified.

   The stereoscopic device MAY use the session-level attribute value for
   on-screen display, for example an audio volume indicaton, channel
   indication or electronic programme guide.




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   Notice that a 2D device that does not support the "ParallaxInfo"
   attribute will ignore it, and therefore display the 2D media data on
   the position as transmitted.
















































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5.  Example

   The following is an example of an SDP description of a session with
   an audio stream, a video stream and a 3GPP timed text stream (see
   [3gpp-tt]), streamed using RTP as per [RFC4396].  If the display
   resolution is 1280x720, the parallax is scaled down with a factor
   F=11952/1280=9.  The transmitted text stream is the L-stream, and
   with the example display resolution each R-view is 144/9=16 pixels on
   the left of the L-view.  This corresponds to the virtual positioning
   of the text in front of the screen.

      v=0
      o=Alice 2890844526 2890842807 IN IP4 131.163.72.4
      s=The technology of 3D-TV
      c=IN IP4 131.164.74.2
      t=0 0
      a=ParallaxInfo:L -180
      m=video 49170 RTP/AVP 99
      a=rtpmap:99 H264/90000
      m=video 52888 RTP/AVP 97
      a=rtpmap:97 3gpp-tt/1000
      a=ParallaxInfo:L -144
      m=audio 52890 RTP/AVP 10
      a=rtpmap:10 L16/16000/2

   Notice that the default value "-180" is overridden by the value
   "-144" for the text stream.  However the "-180" value is still
   signalled for on-screen display of e.g. volume control and other 2D
   graphics.

   In case each R-view is 24 pixels (216 pixels in the reference
   resolution) on the right of the associated L-view, i.e. the virtual
   positioning of the text is behind the screen, then the three lines
   defined for 3gpp-tt can be replaced as follows:

      m=video 52888 RTP/AVP 97
      a=rtpmap:97 3gpp-tt/1000
      a=ParallaxInfo:L 216













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6.  Remarks

   A positive parallax value indicates virtual positioning of the 2D
   media data behind the screen.  This is the case when the objects in
   the L-view are on the left of the same objects in the R-view.
   Similarly, a negative parallax value indicates that the objects in
   the R-view are on the left of the same objects in the L-view, and
   corresponds to virtual positioning in front of the screen.

   Since the "ParallaxInfo" attribute indicates a shift of the
   transmitted stream, it might happen that the L- or R-view trespasses
   the bounderies of the display.  In this case, clipping is necessary,
   as illustrated by Figure 1.

   Similarly, there are areas which are covered by the L-view but not by
   the R-view and vice versa.  These areas need to be filled in a
   sensible way.  Since the "ParallaxInfo" attribute is designed for
   objects that overlay other video data (e.g. subtitles), it is trivial
   to fill in uncovered areas by using the underlying video data.
   However, if there is no underlying video data, other mechanisms to
   fill in the uncovered areas need to be defined.  Definition of these
   mechanisms are out of scope of this document.

      +-----------------------+          +-----------------------+
      |SCREEN       .         |          |SCREEN       .         |
      |             .         |          |             .         |
      |    +-------------------+         |  +-------------------+|
      |    |TEXT     .         |         |  |TEXT     .         ||
      |    +-------------------+         |  +-------------------+|
      |             .         |          |             .         |
      |             .         |          |             .         |
      +-----------------------+          +-----------------------+

                                 |
                                 | CLIP
                                 V

      +-----------------------+          +-----------------------+
      |SCREEN       .         |          |SCREEN       .         |
      |             .         |          |             .         |
      |    +------------------+          |  +-------------------+|
      |    |TEXT     .        |          |  |TEXT     .         ||
      |    +------------------+          |  +-------------------+|
      |             .         |          |             .         |
      |             .         |          |             .         |
      +-----------------------+          +-----------------------+

                                 Figure 1



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   The normalisation of the parallax towards a reference screen width of
   11520 pixels was chosen to ensure correct display of the same stream
   on different video display resolutions.  This is especially useful
   when the underlying video is coded with a scalable video codec, which
   does not have a fixed video resolution.














































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7.  Security Considerations

   The authors foresee no security issues in addition to those already
   listed in [RFC4566].















































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8.  IANA Considerations

   Following the guidelines in [RFC4566], the SDP attribute has to be
   registered at IANA:

   o  Contact name/email: authors of this RFC

   o  Attribute name: ParallaxInfo

   o  Long-form attribute name: Parallax info for the depth positioning
      of 2D media data in the 3D space

   o  Type of attribute: session level and media level

   o  Subject to charset: no

   This attribute is used to signal how 2D media data is to be displayed
   in the 3D space.  It indicates the shift of the respective left and
   right views.

   The attribute has the following ABNF (see [RFC4234]) description:

   ParalaxInfo          = "a=ParallaxInfo:" TransmittedPosition Parallax
   TransmittedPosition  = "C"/"L"/"R"
   Parallax             = num-val

   The attribute transfers this information as two parameters:
   "TransmittedPosition" indicates which view of the 2D media data (left
   "L", right "R" or centre "C") is carried by the stream, and
   "Parallax" signals the parallax (in pixels) of objects in the 2D
   media stream.




















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9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 4234, October 2005.

   [RFC4396]  Rey, J. and Y. Matsui, "RTP Payload Format for 3rd
              Generation Partnership Project (3GPP) Timed Text",
              RFC 4396, February 2006.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [3gpp-tt]  3GPP, "Transparent end-to-end packet switched streaming
              service (PSS); Protocols and codecs (Release 5)",
              TS 26.234 v5.3.0, December 2002.

































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Authors' Addresses

   Bert Greevenbosch
   Huawei Technologies Co., Ltd.
   Huawei Industrial Base
   Bantian, Longgang District
   Shenzhen  518129
   P.R. China

   Phone: +86-755-28978088
   Email: bgreeven@huawei.com


   Hui Yu
   Huawei Technologies Co., Ltd.
   Huawei Nanjing R&D Center
   101 Software Avenue
   Yuhuatai District
   Nanjing  210012
   P.R. China

   Phone: +86-25-56620323
   Email: huiyu@huawei.com




























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