I263

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  • FOURCCs: I263
  • Company: Intel

General description

This codec is based on early drafts of the H.263 standard specification. It supports the following modes: Unrestricted Motion Vector mode, Advanced Prediction mode, PB frames mode, Improved PB frames mode (old version!) and Deblocking Filter mode.

Picture Layer

Data for each picture consists of a picture header followed by data for Group of Blocks, eventually followed by an end-of-sequence code and stuffing bits.

Picture Header

The Picture Header of the I.263 has the following format:

  • Picture Start Code (PSC) (22 bits)

PSC is a word of 22 bits. Its value is 0000 0000 0000 0000 1 00000. All picture start codes shall be byte aligned.

  • Temporal Reference (TR) (8 bits)

An 8-bit number which can have 256 possible values. It is formed by incrementing its value in the previously transmitted picture header by one plus the number of non-transmitted pictures (at 29.97 Hz) since the previously transmitted one. The arithmetic is performed with only the eight LSBs. In the optional PB-frames mode, TR only addresses P-pictures; for the temporal reference for B-pictures refer to section 5.1.7.

  • Marker (1 bit)

This bit should be always set to "1" in order to avoid start code emulation.

  • H.263 ID (1 bit)

This bit should be always set to "0" for distinction with H.261.

  • Split screen indicator (1 bit)

This indicator is not used in the I.263. Just skip this bit.

  • Document camera indicator (1 bit)

This indicator is not used in the I.263. Just skip this bit.

  • Freeze Picture Release (1 bit)

Unused. Just skip this bit.

  • Source Format (3 bits)

Indicates the source format of the picture. Values "000" and "110" are forbidden. "111" indicates the extended PTYPE (see below).

  • Picture type (1 bit)

Picture Coding Type: “0” INTRA (I-picture), “1” INTER (P-picture).

  • Unrestricted Motion Vector mode indicator (1 bit)

Unrestricted Motion Vector mode: “0” off, “1” on.

  • Syntax-based Arithmetic Coding mode (SAC) indicator (1 bit)

Syntax-based Arithmetic Coding mode is not supported in the I.263. Just skip this bit.

  • Advanced Prediction mode indicator (1 bit)

Advanced Prediction mode: “0” off, “1” on.

  • PB-frames mode indicator (1 bit)

PB-frames mode: “0” normal I- or P-picture, “1” PB-frame. If the Picture Type bit (see above) is set to “0”, this bit shall be set to “0” as well.


Extended PTYPE (EPTYPE):

These fields are present only if the Source Format field (see above) indicates the extended PTYPE.

  • Source Format (3 bits)

Values "000" and "111" are forbidden. "110" indicates that the custom source format (CSFMT) extension is present (see below).

  • Unknown flags (2 bits)

These bits should be always set to "0". They have no meaning. Just skip them.

  • Deblocking Filter mode indicator (1 bit)

Deblocking Filter mode: “0” off, “1” on.

  • Unknown flag (1 bit)

This bit should be always set to "0". It has no meaning. Just skip it.

  • Improved PB-frames mode indicator (1 bit)

Improved PB-frames mode: “0” off, “1” on. For description of this mode see below.

  • Unknown flags (5 bits)

These bits should be always set to "0". They have no meaning. Just skip them.

  • Unknown Marker (5 bits)

The value of this bits should be always set to "00001".


Custom source format (CSFMT) extension

This extension is present only if indicated by the Source Format field of the Extended PTYPE (EPTYPE) (see above).

  • Pixel Aspect Ratio code (4 bits)

Aspect ratios: "0001" - 1:1, "0010" - 12:11 (CIF 4:3), "0011" - 10:11 (525-type 4:3), "1111" - extended PAR (see below; probably never used because of an internal bug in the I.263 driver). Other values are forbidden.

  • Picture width (9 bits)

The width of the encoded picture = (value of this field + 1) * 4

  • Marker (1 bit)

Equal to "1" to prevent start code emulation.

  • Picture height (9 bits)

The height of the encoded picture = (value of this field + 1) * 4

Extended Pixel Aspect Ratio (EPAR)

The following bits are present if CSFMT extension (see above) is present and extended PAR is indicated therein. When present, EPAR consists of:

  • Pixel Aspect ratio width (8 bits)

The natural binary representation of the PAR width; "0" is forbidden.

  • Pixel Aspect ratio height (8 bits)

The natural binary representation of the PAR height; "0" is forbidden.


  • Quantizer Information (PQUANT) (5 bits)

A fixed length codeword of 5 bits which indicates the quantizer QUANT to be used for the picture until updated by any subsequent GQUANT or DQUANT. The codewords are the natural binary representations of the values of QUANT which, being half the step sizes, range from 1 to 31.