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1.1 Glossary

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This document uses the following terms:

big-endian: Multiple-byte values that are byte-ordered with the most significant byte stored in the memory location with the lowest address.

BitStream: A sequence of bits that represents the compressed data for a full-text index catalog.

Common Interface Format (CIF): For H.263, a picture consisting of 352x288 pixels for luminance and 176x144 pixels for chrominance.

Common Intermediate Format (CIF): A picture format, described in the H.263 standard, that is used to specify the horizontal and vertical resolutions of pixels in YCbCr sequences in video signals.

draft mode: A mode that is specified by H26XPF video streams extensions for encapsulating H.263 video streams. Draft mode is used in conjunction with the H.323 [H323] application layer control protocol, and it supports an H.263 payload header format that is different from the format in RFC mode.

group of blocks (GOB): For H.263, k*16 lines, where k equals 1 for QCIF, and CIF.

group of blocks number (GOBN): GOB number in effect at the start of the packet.

interframe: A video frame that is intercoded, also called a P-Frame or P-picture. Refer to [H261] and [H263] for details concerning P-picture.

intraframe: A video frame that is intracoded, also called an I-Frame or I-picture. Refer to [H261] and [H263] for details concerning I-picture.

luminance: The luminous intensity of a surface in a given direction per unit of projected area.

macro block (MB): A macro block consists of four blocks of luminance and the spatially corresponding two blocks of chrominance. Each block is arranged in an 8x8 pixel configuration.

mode A: The H.263 mode A payload header, which consists of four bytes, and is present before the actual compression of the H.263 video bitstream in a packet. It allows for fragmentation at GOB boundaries.

mode B: The H.263 mode B payload header, which consists of eight bytes, and starts at the luminance boundaries without the PB-frames option.

mode C: The H.263 mode C payload header, which consists of twelve bytes to support fragmentation at macro block (MB) boundaries for frames that are coded with the PB-frames option.

PB-Frame: A P frame and a B frame, which are coded into one bitstream with macro blocks from the two frames interleaved. In a packet, an MB from the P frame and an MB from the B frame must be treated together, because each MB for the B frame is coded based on the corresponding MB for the P frame. A means must be provided to ensure proper rendering of two frames in the right order. Additionally, if any part of this combined bitstream is lost, it will affect both frames, and possibly more.

quantization: The process of approximating the continuous set of values in the image data with a finite set of values.

Quarter Common Interface Format (QCIF): For H.263, a picture consisting of 176x144 pixels for luminance and 88x72 pixels for chrominance.

RFC Mode: A mode that is specified by H26XPF video streams extensions for encapsulating H.263 video streams. RFC mode is used in conjunction with the Session Initiation Protocol (SIP) [MS-SIP] application layer control protocol, and it supports an H.263 payload header format that is different from the format in draft mode.

Sub Quarter Common Interface Format (SQCIF): For H.263, a picture consisting of 128x96 pixels for luminance and 64x48 pixels for chrominance.

MAY, SHOULD, MUST, SHOULD NOT, MUST NOT: These terms (in all caps) are used as defined in [RFC2119]. All statements of optional behavior use either MAY, SHOULD, or SHOULD NOT.