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Speer 2 Audio-Video Transport Working Group Don Hoffman 3 draft-ietf-avt-cellb-08.txt Sun Microsystems, Inc. 4 July 7th, 1996 5 Expires: January 7th, 1997 7 RTP Payload Format of Sun's CellB Video Encoding 9 Status of this Memo 11 This document is an Internet Draft. Internet Drafts are working documents 12 of the Internet Engineering Task Force (IETF), its Areas, and its Working 13 Groups. Note that other groups may also distribute working documents as 14 Internet Drafts. 16 Internet Drafts are draft documents valid for a maximum of six months. 17 Internet Drafts may be updated, replaced, or obsoleted by other documents 18 at any time. It is not appropriate to use Internet Drafts as reference 19 material or to cite them other than as a ``working draft'' or ``work in 20 progress.'' 22 Please check the I-D abstract listing contained in each Internet Draft 23 directory to learn the current status of this or any other Internet Draft. 25 Distribution of this document is unlimited. 27 Abstract 29 This draft describes a packetization scheme for the CellB video 30 encoding. The scheme proposed allows applications to transport 31 CellB video flows over protocols used by RTP. This document is 32 meant for implementors of video applications that want to use RTP 33 and CellB. 35 1 Introduction 37 The Cell image compression algorithm is a variable bit-rate video 38 coding scheme. It provides "high" quality, low bit-rate image 39 compression at low computational cost. The bytestream that is 40 produced by the Cell encoder consists of instructional codes and 41 information about the compressed image. 43 For futher information on Cell compression technology, refer to [1]. 44 Currently, there are two versions of the Cell compression technology: 45 CellA and CellB. CellA is primarily designed for the encoding of 46 stored video intended for local display, and will not be discussed in 47 this memo. 49 CellB, derived from CellA, has been optimized for network-based video 50 applications. It is computationally symmetric in both encode and 51 decode. CellB utilizes a fixed colormap and vector quantization 52 techniques in the YUV color space to achieve compression. 54 2 Network Packetization and Encapsulation 56 2.1 RTP Usage 58 The RTP timestamp is in units of 90KHz. The same timestamp value is used 59 for all packet payloads of a frame. The RTP maker bit denotes the end of 60 a frame. 62 2.2 CellB Header 64 The packetization of the CellB bytestream is designed to make the 65 resulting packet stream robust to packet loss. To achieve this goal, an 66 additional header is added to each RTP packet to uniquely identify the 67 location of the first cell of the packet within the current frame. In 68 addition, the width and height of the frame in pixels is carried in each 69 CellB packet header. Although the size can only change between frames, 70 it is carried in every packet to simplify the packet encoding. 72 0 1 2 3 73 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 74 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 75 | Cell X Location | Cell Y Location | 76 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 77 | Width of Image | Height of Image | 78 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 79 | Compressed CellB Data | 80 | .... | 81 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 82 All fields are 16-bit unsigned integers in network byte order, and are 83 placed at the beginning of the payload for each RTP packet. The Cell X and 84 the Cell Y Location coordinates are expressed as cell coordinates, not pixel 85 coordinates. Since cells represent 4x4 blocks of pixels, the X or Y dimension 86 of the cell coordinates range in value from 0 through 1/4 of the of the 87 same dimension in pixel coordinates. 89 2.3 Packetization Rules 91 A packet can be of any size chosen by the implementor, up to a full 92 frame. All multi-byte codes must be completely contained within a 93 packet. In general, the implementor should avoid packet sizes that 94 result in fragmentation by the network. 96 3 References 98 1. "Cell Image Compression Byte Stream Description," 99 ftp://playground.sun.com:/pub/multimedia/video/ 100 cellbytestream.ps.Z 102 2. Thierry Turletti, Christian Huitema INRIA, "RTP 103 Packetization of H.261 Video Streams", Internet Draft, 104 March 8th, 1995. 106 3. H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson, 107 "RTP: A Transport Protocol for Real-Time Applications", 108 Internet RFC 1889 110 4. H. Schulzrinne, "RTP Profile for Audio and Video Conferences 111 with Minimal Control", Internet RFC 1890 113 4 Address of the Authors 115 Michael F. Speer 116 Sun Microsystems Computer Corporation 117 2550 Garcia Ave MailStop UMPK14-305 118 Mountain View, CA 94043 120 Voice: +1 415 786 6368 121 Fax: +1 415 786 6445 122 E-mail: michael.speer@eng.sun.com 124 Don Hoffman 125 Sun Microsystems Computer Corporation 126 2550 Garcia Ave MailStop UMPK14-305 127 Mountain View, CA 94043 129 Voice: +1 415 786 6370 130 Fax: +1 415 786 6445 131 E-mail: don.hoffman@eng.sun.com 133 Appendix A - Structure of the CellB Video Stream 135 The CellB bytestream consists of cell codes, skip codes and 136 quantization-table specific codes. These are now described. 138 A.1 CellB Cell Code 140 Cell codes are 4 bytes in length, and describe a 4x4 pixel cell. There 141 are two possible luminance (Y) levels for each cell, but only one pair 142 of chrominance (UV) values. The CellB cell code is shown below: 144 0 1 2 3 145 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 146 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 147 |0 M M M M M M M M M M M M M M M|U V U V U V U V|Y Y Y Y Y Y Y Y| 148 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 149 4x4 Bitmask U/V Code Y/Y Code 151 The first two bytes of the cell code are a bitmask. Each bit in the 152 mask represents a pixel in a 16-pixel cell. Bit 0 represents the value 153 of the upper right-hand pixel of the cell, and subsequent bits represent 154 the pixels in row-major order. If a pixel's bit is set in the 4x4 155 Bitmask, then the pixel will be rendered with the pixel value . If the pixel's bit is not set in the bitmask, then the pixel's 157 value will be rendered with the value . The bitmask for 158 the cell is normalized so that the most significant bit is always 0 (i.e., 159 corresponding to ). 161 The U/V field of the cell code represents the chrominance component. This 162 code is in index into a table of vectors that represents two independent 163 components of chrominance. 165 The Y/Y field of the cell code represents two luminance values (Y(0) and Y(1)). 166 This code is an index into a table of two-compoment luminance vectors. 168 The derivation of the U/V and Y/Y tables is outside the scope of this 169 memo. A complete discussion can be found in [1]. 171 A.2 CellB Skip Code 173 The single byte CellB skip code tells the CellB decoder to skip the 174 next S+1 cells in the current video frame being decoded. The maximum 175 number of cells that can be skipped is 32. The format of the skip code 176 is shown below. 178 0 1 2 3 4 5 6 7 180 +-+-+-+-+-+-+-+-+ 181 |1 0 0 S S S S S| 182 +-+-+-+-+-+-+-+-+ 184 A.3 CellB Y/Y Table Code 186 The single byte "new Y/Y table" code is used to tell the decoder that the 187 next 512 bytes are a new Y/Y quantization table. The code and the 188 representation of the table are shown below. The sample encoder/decoder pair 189 in this document do not implement this feature of the CellB compression. 190 However, future CellB codecs may implement this feature. 192 0 1 2 3 4 5 6 7 193 +-+-+-+-+-+-+-+-+ 194 |1 1 1 1 1 1 1 0| 195 +-+-+-+-+-+-+-+-+ 197 The format of the new Y/Y table is: 199 0 1 2 3 200 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 202 | Y1_000 | Y2_000 | Y1_001 | Y2_001 | 203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 205 . 206 . 207 . 209 0 1 2 3 210 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 211 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 212 | Y1_254 | Y2_254 | Y1_255 | Y2_255 | 213 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 215 A.4 CellB U/V Table Code 217 The single byte "new U/V table" code is used to tell the decoder that the 218 next 512 bytes represent a new U/V quantization table. The code is shown 219 below. The sample encoder/decoder pair provided in this document do not 220 implement this feature of the CellB compression. However, future CellB 221 codecs may implement this feature. 223 0 1 2 3 4 5 6 7 224 v +-+-+-+-+-+-+-+-+ 225 |1 1 1 1 1 1 1 1| 226 +-+-+-+-+-+-+-+-+ 228 The bytes of the new U/V quantization table are arranged as: 230 0 1 2 3 231 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 232 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 233 | U_000 | V_000 | U_001 | V_001 | 234 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 236 . 237 . 238 . 240 0 1 2 3 241 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 242 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 243 | U_254 | V_254 | U_255 | V_255 | 244 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 246 Appendix B - Availability of CellB 248 It is the viewpoint of Sun Microsystems, Inc, that CellB is publically 249 available for use without any license.