(registered by RFC 3555, updated by RFC4629)

Type name: video

Subtype name: H263-1998

Required parameters: None

Optional parameters:

   SQCIF: Specifies the MPI (Minimum Picture Interval) for SQCIF
   resolution.  Permissible values are integer values from 1 to 32,
   which correspond to a maximum frame rate of 30/(1.001 * the
   specified value) frames per second.

   QCIF: Specifies the MPI (Minimum Picture Interval) for QCIF
   resolution.  Permissible values are integer values from 1 to 32,
   which correspond to a maximum frame rate of 30/(1.001 * the
   specified value) frames per second.

   CIF: Specifies the MPI (Minimum Picture Interval) for CIF
   resolution.  Permissible values are integer values from 1 to 32,
   which correspond to a maximum frame rate of 30/(1.001 * the
   specified value) frames per second.

   CIF4: Specifies the MPI (Minimum Picture Interval) for 4CIF
   resolution.  Permissible values are integer values from 1 to 32,
   which correspond to a maximum frame rate of 30/(1.001 * the
   specified value) frames per second.

   CIF16: Specifies the MPI (Minimum Picture Interval) for 16CIF
   resolution.  Permissible values are integer values from 1 to 32,
   which correspond to a maximum frame rate of 30/(1.001 * the
   specified value) frames per second.

   CUSTOM: Specifies the MPI (Minimum Picture Interval) for a
   custom-defined resolution.  The custom parameter receives three
   comma-separated values, Xmax, Ymax, and MPI.  The Xmax and Ymax
   parameters describe the number of pixels in the X and Y axis and
   must be evenly divisible by 4.  The permissible values for MPI are
   integer values from 1 to 32, which correspond to a maximum frame
   rate of 30/(1.001 *the specified value).

   A system that declares support of a specific MPI for one of the
   resolutions SHALL also implicitly support a lower resolution with
   the same MPI.

   A list of optional annexes specifies which annexes of H.263 are
   supported.  The optional annexes are defined as part of H263-1998,
   H263-2000.  H.263 annex X [H263] defines profiles that group
   annexes for specific applications.  A system that supports a
   specific annex SHALL specify its support using the optional
   parameters.  If no annex is specified, then the stream is Baseline
   H.263.

   The allowed optional parameters for the annexes are "F", "I", "J",
   "T", "K", "N", and "P".

   "F", "I", "J", and "T" if supported, SHALL have the value "1".  If
   not supported, they should not be listed or SHALL have the value
   "0".

   "K" can receive one of four values 1 - 4:

   1: Slices In Order, Non-Rectangular

   2: Slices In Order, Rectangular

   3: Slices Not Ordered, Non-Rectangular

   4: Slices Not Ordered, Rectangular

   "N": Reference Picture Selection mode -  Four numeric choices
   (1 - 4) are available, representing the following modes:

   1: NEITHER:  No back-channel data is returned from the decoder to
      the encoder.

   2: ACK:  The decoder returns only acknowledgment messages.

   3: NACK:  The decoder returns only non-acknowledgment messages.

   4: ACK+NACK:  The decoder returns both acknowledgment and non-
      acknowledgment messages.

   No special provision is made herein for carrying back channel
   information.  The Extended RTP Profile for RTCP-based Feedback
   [RFC4585] MAY be used as a back channel mechanism.

   "P": Reference Picture Resampling, in which the following submodes
   are represented as a number from 1 to 4:

   1: dynamicPictureResizingByFour

   2: dynamicPictureResizingBySixteenthPel

   3: dynamicWarpingHalfPel

   4: dynamicWarpingSixteenthPel

   Example: P=1,3

   PAR: Arbitrary Pixel Aspect Ratio.  Defines the width:height ratio
   by two colon-separated integers between 0 and 255.  Default ratio
   is 12:11, if not otherwise specified.

   CPCF: Arbitrary (Custom) Picture Clock Frequency: CPCF is a
   comma-separated list of eight parameters specifying a custom
   picture clock frequency and the MPI (minimum picture interval) for
   the supported picture sizes when using that picture clock
   frequency.  The first two parameters are cd, which is an integer
   from 1 to 127, and cf, which is either 1000 or 1001.  The custom
   picture clock frequency is given by the formula 1800000/(cd*cf)
   provided in the RTP Timestamp semantics in Section 3.1 above (as
   specified in H.263 section 5.1.7).  Following the values of cd and
   cf, the remaining six parameters are SQCIFMPI, QCIFMPI, CIFMPI,
   CIF4MPI, CIF16MPI, and CUSTOMMPI, which each specify an integer
   MPI (minimum picture interval) for the standard picture sizes
   SQCIF, QCIF, CIF, 4CIF, 16CIF, and CUSTOM, respectively, as
   described above.  The MPI value indicates a maximum frame rate of
   1800000/(cd*cf*MPI) frames per second for MPI parameters having a
   value in the range from 1 to 2048, inclusive.  An MPI value of 0
   specifies that the associated picture size is not supported for
   the custom picture clock frequency.  If the CUSTOMMPI parameter is
   not equal to 0, the CUSTOM parameter SHALL also be present (so
   that the Xmax and Ymax dimensions of the custom picture size are
   defined).

   BPP: BitsPerPictureMaxKb.  Maximum number of bits in units of 1024
   bits allowed to represent a single picture.  If this parameter is
   not present, then the default value, based on the maximum
   supported resolution, is used.  BPP is integer value between 0 and
   65536.

   HRD: Hypothetical Reference Decoder.  See annex B of H.263
   specification [H263].  This parameter, if supported, SHALL have
   the value "1".  If not supported, it should not be listed or SHALL
   have the value "0".

Encoding considerations:

   This media type is framed and binary; see Section 4.8 in [RFC4288]

Security considerations: See Section 11 of RFC 4629

Interoperability considerations:

   These are receiver options; current implementations will not send
   any optional parameters in their SDP.  They will ignore the
   optional parameters and will encode the H.263 stream without any
   of the annexes.  Most decoders support at least QCIF and CIF fixed
   resolutions, and they are expected to be available almost in every
   H.263-based video application.

Published specification: RFC 4629

Applications that use this media type:

   Audio and video streaming and conferencing tools.

   Additional information: None

   Person and email address to contact for further information:

Roni Even: roni.even&polycom.co.il

   Intended usage: COMMON

   Restrictions on usage:

   This media type depends on RTP framing and thus is only defined
   for transfer via RTP [RFC3550].  Transport within other framing
   protocols is not defined at this time.

Author: Roni Even

Change controller:

   IETF Audio/Video Transport working group, delegated from the IESG.