Movatterモバイル変換

Network Working Group                                            L. BercRequest for Comments: 2035                 Digital Equipment CorporationCategory: Standards Track                                      W. Fenner                                                              Xerox PARC                                                            R. Frederick                                                              Xerox PARC                                                              S. McCanne                                            Lawrence Berkeley Laboratory                                                            October 1996RTP Payload Format for JPEG-compressed VideoStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Abstract   This memo describes the RTP payload format for JPEG video streams.   The packet format is optimized for real-time video streams where   codec parameters change rarely from frame to frame.   This document is a product of the Audio-Video Transport working group   within the Internet Engineering Task Force.  Comments are solicited   and should be addressed to the working group's mailing list at rem-   conf@es.net and/or the author(s).1.  Introduction   The Joint Photographic Experts Group (JPEG) standard [1,2,3] defines   a family of compression algorithms for continuous-tone, still images.   This still image compression standard can be applied to video by   compressing each frame of video as an independent still image and   transmitting them in series.  Video coded in this fashion is often   called Motion-JPEG.   We first give an overview of JPEG and then describe the specific   subset of JPEG that is supported in RTP and the mechanism by which   JPEG frames are carried as RTP payloads.   The JPEG standard defines four modes of operation: the sequential DCT   mode, the progressive DCT mode, the lossless mode, and the   hierarchical mode.  Depending on the mode, the image is representedBerc, et. al.               Standards Track                     [Page 1]

RFC 2035           RTP Payload Format for JPEG Video        October 1996   in one or more passes.  Each pass (called a frame in the JPEG   standard) is further broken down into one or more scans.  Within each   scan, there are one to four components,which represent the three   components of a color signal (e.g., "red, green, and blue", or a   luminance signal and two chromanince signals).  These components can   be encoded as separate scans or interleaved into a single scan.   Each frame and scan is preceded with a header containing optional   definitions for compression parameters like quantization tables and   Huffman coding tables.  The headers and optional parameters are   identified with "markers" and comprise a marker segment; each scan   appears as an entropy-coded bit stream within two marker segments.   Markers are aligned to byte boundaries and (in general) cannot appear   in the entropy-coded segment, allowing scan boundaries to be   determined without parsing the bit stream.   Compressed data is represented in one of three formats: the   interchange format, the abbreviated format, or the table-   specification format.  The interchange format contains definitions   for all the table used in the by the entropy-coded segments, while   the abbreviated format might omit some assuming they were defined   out-of-band or by a "previous" image.   The JPEG standard does not define the meaning or format of the   components that comprise the image.  Attributes like the color space   and pixel aspect ratio must be specified out-of-band with respect to   the JPEG bit stream.  The JPEG File Interchange Format (JFIF) [4] is   a defacto standard that provides this extra information using an   application marker segment (APP0).  Note that a JFIF file is simply a   JPEG interchange format image along with the APP0 segment.  In the   case of video, additional parameters must be defined out-of-band   (e.g., frame rate, interlaced vs. non-interlaced, etc.).   While the JPEG standard provides a rich set of algorithms for   flexible compression, cost-effective hardware implementations of the   full standard have not appeared.  Instead, most hardware JPEG video   codecs implement only a subset of the sequential DCT mode of   operation.  Typically, marker segments are interpreted in software   (which "re-programs" the hardware) and the hardware is presented with   a single, interleaved entropy-coded scan represented in the YUV color   space.2.  JPEG Over RTP   To maximize interoperability among hardware-based codecs, we assume   the sequential DCT operating mode [1,Annex F] and restrict the set of   predefined RTP/JPEG "type codes" (defined below) to single-scan,   interleaved images.  While this is more restrictive than evenBerc, et. al.               Standards Track                     [Page 2]

RFC 2035           RTP Payload Format for JPEG Video        October 1996   baseline JPEG, many hardware implementation fall short of the   baseline specification (e.g., most hardware cannot decode non-   interleaved scans).   In practice, most of the table-specification data rarely changes from   frame to frame within a single video stream.  Therefore, RTP/JPEG   data is represented in abbreviated format, with all of the tables   omitted from the bit stream.  Each image begins immediately with the   (single) entropy-coded scan.  The information that would otherwise be   in both the frame and scan headers is represented entirely within a   64-bit RTP/JPEG header (defined below) that lies between the RTP   header and the JPEG scan and is present in every packet.   While parameters like Huffman tables and color space are likely to   remain fixed for the lifetime of the video stream, other parameters   should be allowed to vary, notably the quantization tables and image   size (e.g., to implement rate-adaptive transmission or allow a user   to adjust the "quality level" or resolution manually).  Thus explicit   fields in the RTP/JPEG header are allocated to represent this   information.  Since only a small set of quantization tables are   typically used, we encode the entire set of quantization tables in a   small integer field.  The image width and height are encoded   explicitly.   Because JPEG frames are typically larger than the underlying   network's maximum packet size, frames must often be fragmented into   several packets.  One approach is to allow the network layer below   RTP (e.g., IP) to perform the fragmentation.  However, this precludes   rate-controlling the resulting packet stream or partial delivery in   the presence of loss.  For example, IP will not deliver a fragmented   datagram to the application if one or more fragments is lost, or IP   might fragment an 8000 byte frame into a burst of 8 back-to-back   packets.  Instead, RTP/JPEG defines a simple fragmentation and   reassembly scheme at the RTP level.3.  RTP/JPEG Packet Format   The RTP timestamp is in units of 90000Hz.  The same timestamp must   appear across all fragments of a single frame.  The RTP marker bit is   set in the last packet of a frame.Berc, et. al.               Standards Track                     [Page 3]

RFC 2035           RTP Payload Format for JPEG Video        October 19963.1.  JPEG header   A special header is added to each packet that immediately follows the   RTP header:    0                   1                   2                   3    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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   | Type specific |              Fragment Offset                  |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |      Type     |       Q       |     Width     |     Height    |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+3.1.1.  Type specific: 8 bits   Interpretation depends on the value of the type field.3.1.2.  Fragment Offset: 24 bits   The Fragment Offset is the data offset in bytes of the current packet   in the JPEG scan.3.1.3.  Type: 8 bits   The type field specifies the information that would otherwise be   present in a JPEG abbreviated table-specification as well as the   additional JFIF-style parameters not defined by JPEG.  Types 0-127   are reserved as fixed, well-known mappings to be defined by this   document and future revisions of this document.  Types 128-255 are   free to be dynamically defined by a session setup protocol (which is   beyond the scope of this document).3.1.4.  Q: 8 bits   The Q field defines the quantization tables for this frame using an   algorithm that determined by the Type field (see below).3.1.5.  Width: 8 bits   This field encodes the width of the image in 8-pixel multiples (e.g.,   a width of 40 denotes an image 320 pixels wide).3.1.6.  Height: 8 bits   This field encodes the height of the image in 8-pixel multiples   (e.g., a height of 30 denotes an image 240 pixels tall).Berc, et. al.               Standards Track                     [Page 4]

RFC 2035           RTP Payload Format for JPEG Video        October 19963.1.7.  Data   The data following the RTP/JPEG header is an entropy-coded segment   consisting of a single scan.  The scan header is not present and is   inferred from the RTP/JPEG header.  The scan is terminated either   implicitly (i.e., the point at which the image is fully parsed), or   explicitly with an EOI marker.  The scan may be padded to arbitrary   length with undefined bytes.  (Existing hardware codecs generate   extra lines at the bottom of a video frame and removal of these lines   would require a Huffman-decoding pass over the data.)   As defined by JPEG, restart markers are the only type of marker that   may appear embedded in the entropy-coded segment.  The "type code"   determines whether a restart interval is defined, and therefore   whether restart markers may be present. It also determines if the   restart intervals will be aligned with RTP packets, allowing for   partial decode of frames, thus increasing resiliance to packet drop.   If restart markers are present, the 6-byte DRI segment (define   restart interval marker [1, Sec. B.2.4.4] precedes the scan).   JPEG markers appear explicitly on byte aligned boundaries beginning   with an 0xFF.  A "stuffed" 0x00 byte follows any 0xFF byte generated   by the entropy coder [1, Sec. B.1.1.5].4.  Discussion4.1.  The Type Field   The Type field defines the abbreviated table-specification and   additional JFIF-style parameters not defined by JPEG, since they are   not present in the body of the transmitted JPEG data.  The Type field   must remain constant for the duration of a session.   Six type codes are currently defined.  They correspond to an   abbreviated table-specification indicating the "Baseline DCT   sequential" mode, 8-bit samples, square pixels, three components in   the YUV color space, standard Huffman tables as defined in [1, Annex   K.3], and a single interleaved scan with a scan component selector   indicating components 0, 1, and 2 in that order.  The Y, U, and V   color planes correspond to component numbers 0, 1, and 2,   respectively.  Component 0 (i.e., the luminance plane) uses Huffman   table number 0 and quantization table number 0 (defined below) and   components 1 and 2 (i.e., the chrominance planes) use Huffman table   number 1 and quantization table number 1 (defined below).   Additionally, video is non-interlaced and unscaled (i.e., the aspect   ratio is determined by the image width and height).  The frame rate   is variable and explicit via the RTP timestamp.Berc, et. al.               Standards Track                     [Page 5]

RFC 2035           RTP Payload Format for JPEG Video        October 1996   Six RTP/JPEG types are currently defined that assume all of the   above.  The odd types have different JPEG sampling factors from the   even ones:                        horizontal   vertical           types   comp  samp. fact. samp. fact.          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+          |  0/2/4  |  0  |     2     |   1   |          |  0/2/4  |  1  |     1     |   1   |          |  0/2/4  |  2  |     1     |   1   |          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+          |  1/3/5  |  0  |     2     |   2   |          |  1/3/5  |  1  |     1     |   1   |          |  1/3/5  |  2  |     1     |   1   |          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   These sampling factors indicate that the chromanince components of   type 0/2/4 video is downsampled horizontally by 2 (often called   4:2:2) while the chrominance components of type 1/3/5 video are   downsampled both horizontally and vertically by 2 (often called   4:2:0).   The three pairs of types (0/1), (2/3) and (4/5) differ from each   other as follows:   0/1 : No restart markers are present in the entropy data.         No restriction is placed on the fragmentation of the stream         into RTP packets.         The type specific field is unused and must be zero.   2/3 : Restart markers are present in the entropy data.         The entropy data is preceded by a DRI marker segment, defining         the restart interval.         No restriction is placed on the fragmentation of the stream         into RTP packets.         The type specific field is unused and must be zero.Berc, et. al.               Standards Track                     [Page 6]

RFC 2035           RTP Payload Format for JPEG Video        October 1996   4/5 : Restart markers are present in the entropy data.         The entropy data is preceded by a DRI marker segment, defining         the restart interval.         Restart intervals are be sent as separate (possibly multiple)         RTP packets.         The type specific field (TSPEC) is used as follows:             A restart interval count (RCOUNT) is defined, which             starts at zero, and is incremented for each restart             interval in the frame.             The first packet of a restart interval gets TSPEC = RCOUNT.             Subsequent packets of the restart interval get TSPEC = 254,             except the final packet, which gets TSPEC = 255.   Additional types in the range 128-255 may be defined by external   means, such as a session protocol.Appendix B contains C source code for transforming the RTP/JPEG   header parameters into the JPEG frame and scan headers that are   absent from the data payload.4.2.  The Q Field   The quantization tables used in the decoding process are   algorithmically derived from the Q field.  The algorithm used depends   on the type field but only one algorithm is currently defined for the   two types.   Both type 0 and type 1 JPEG assume two quantizations tables.  These   tables are chosen as follows.  For 1 <= Q <= 99, the Independent JPEG   Group's formula [5] is used to produce a scale factor S as:        S = 5000 / Q          for  1 <= Q <= 50          = 200 - 2 * Q       for 51 <= Q <= 99   This value is then used to scale Tables K.1 and K.2 from [1]   (saturating each value to 8-bits) to give quantization table numbers   0 and 1, respectively.  C source code is provided inAppendix A to   compute these tables.   For Q >= 100, a dynamically defined quantization table is used, which   might be specified by a session setup protocol.  (This session   protocol is beyond the scope of this document).  It is expected that   the standard quantization tables will handle most cases in practice,   and dynamic tables will be used rarely.  Q = 0 is reserved.Berc, et. al.               Standards Track                     [Page 7]

RFC 2035           RTP Payload Format for JPEG Video        October 19964.3.  Fragmentation and Reassembly   Since JPEG frames are large, they must often be fragmented.  Frames   should be fragmented into packets in a manner avoiding fragmentation   at a lower level.  When using restart markers, frames should be   fragmented such that each packet starts with a restart interval (see   below).   Each packet that makes up a single frame has the same timestamp.  The   fragment offset field is set to the byte offset of this packet within   the original frame.  The RTP marker bit is set on the last packet in   a frame.   An entire frame can be identified as a sequence of packets beginning   with a packet having a zero fragment offset and ending with a packet   having the RTP marker bit set.  Missing packets can be detected   either with RTP sequence numbers or with the fragment offset and   lengths of each packet.  Reassembly could be carried out without the   offset field (i.e., using only the RTP marker bit and sequence   numbers), but an efficient single-copy implementation would not   otherwise be possible in the presence of misordered packets.   Moreover, if the last packet of the previous frame (containing the   marker bit) were dropped, then a receiver could not detect that the   current frame is entirely intact.4.4.  Restart Markers   Restart markers indicate a point in the JPEG stream at which the   Huffman codec and DC predictors  are reset, allowing partial decoding   starting at that point.  The use of restart markers allows for   robustness in the face of packet loss.   RTP/JPEG Types 4/5 allow for partial decode of frames, due to the   alignment of restart intervals with RTP packets. The decoder knows it   has a whole restart interval when it gets sequence of packets with   contiguous RTP sequence numbers, starting with TSPEC<254 (RCOUNT) and   either ending with TSPEC==255, or TSPEC<255 and next packet's   TSPEC<254 (or end of frame).   It can then decompress the RST interval, and paint it. The X and Y   tile offsets of the first MCU in the interval are given by:   tile_offset = RCOUNT * restart_interval * 2   x_offset    = tile_offset % frame_width_in_tiles   y_offset    = tile_offset / frame_width_in_tiles   The MCUs in a restart interval may span multiple tile rows.Berc, et. al.               Standards Track                     [Page 8]

RFC 2035           RTP Payload Format for JPEG Video        October 1996   Decoders can, however, treat types 4/5 as types 2/3, simply   reassembling the entire frame and then decoding.5.  Security Considerations   Security issues are not discussed in this memo.6.  Authors' Addresses   Lance M. Berc   Systems Research Center   Digital Equipment Corporation   130 Lytton Ave   Palo Alto CA 94301   Phone: +1 415 853 2100   EMail: berc@pa.dec.com   William C. Fenner   Xerox PARC   3333 Coyote Hill Road   Palo Alto, CA 94304   Phone: +1 415 812 4816   EMail: fenner@cmf.nrl.navy.mil   Ron Frederick   Xerox PARC   3333 Coyote Hill Road   Palo Alto, CA 94304   Phone: +1 415 812 4459   EMail: frederick@parc.xerox.com   Steven McCanne   Lawrence Berkeley Laboratory   M/S 46A-1123   One Cyclotron Road   Berkeley, CA 94720   Phone: +1 510 486 7520   EMail: mccanne@ee.lbl.govBerc, et. al.               Standards Track                     [Page 9]

RFC 2035           RTP Payload Format for JPEG Video        October 19967.  References[1]  ISO DIS 10918-1. Digital Compression and Coding of Continuous-tone     Still Images (JPEG), CCITT Recommendation T.81.[2]  William B. Pennebaker, Joan L. Mitchell, JPEG: Still Image Data     Compression Standard, Van Nostrand Reinhold, 1993.[3]  Gregory K. Wallace, The JPEG Sill Picture Compression Standard,     Communications of the ACM, April 1991, Vol 34, No. 1, pp. 31-44.[4]  The JPEG File Interchange Format.  Maintained by C-Cube Microsys-     tems, Inc., and available inftp://ftp.uu.net/graphics/jpeg/jfif.ps.gz.[5]  Tom Lane et. al., The Independent JPEG Group software JPEG codec.     Source code available inftp://ftp.uu.net/graphics/jpeg/jpegsrc.v5.tar.gz.Berc, et. al.               Standards Track                    [Page 10]

RFC 2035           RTP Payload Format for JPEG Video        October 1996Appendix A   The following code can be used to create a quantization table from a   Q factor:/* * Table K.1 from JPEG spec. */static const int jpeg_luma_quantizer[64] = {        16, 11, 10, 16, 24, 40, 51, 61,        12, 12, 14, 19, 26, 58, 60, 55,        14, 13, 16, 24, 40, 57, 69, 56,        14, 17, 22, 29, 51, 87, 80, 62,        18, 22, 37, 56, 68, 109, 103, 77,        24, 35, 55, 64, 81, 104, 113, 92,        49, 64, 78, 87, 103, 121, 120, 101,        72, 92, 95, 98, 112, 100, 103, 99};/* * Table K.2 from JPEG spec. */static const int jpeg_chroma_quantizer[64] = {        17, 18, 24, 47, 99, 99, 99, 99,        18, 21, 26, 66, 99, 99, 99, 99,        24, 26, 56, 99, 99, 99, 99, 99,        47, 66, 99, 99, 99, 99, 99, 99,        99, 99, 99, 99, 99, 99, 99, 99,        99, 99, 99, 99, 99, 99, 99, 99,        99, 99, 99, 99, 99, 99, 99, 99,        99, 99, 99, 99, 99, 99, 99, 99};/* * Call MakeTables with the Q factor and two int[64] return arrays */voidMakeTables(int q, u_char *lum_q, u_char *chr_q){  int i;  int factor = q;  if (q < 1) factor = 1;  if (q > 99) factor = 99;  if (q < 50)    q = 5000 / factor;  else    q = 200 - factor*2;Berc, et. al.               Standards Track                    [Page 11]

RFC 2035           RTP Payload Format for JPEG Video        October 1996  for (i=0; i < 64; i++) {    int lq = ( jpeg_luma_quantizer[i] * q + 50) / 100;    int cq = ( jpeg_chroma_quantizer[i] * q + 50) / 100;    /* Limit the quantizers to 1 <= q <= 255 */    if ( lq < 1) lq = 1;    else if ( lq > 255) lq = 255;    lum_q[i] = lq;    if ( cq < 1) cq = 1;    else if ( cq > 255) cq = 255;    chr_q[i] = cq;  }}Appendix B   The following routines can be used to create the JPEG marker segments   corresponding to the table-specification data that is absent from the   RTP/JPEG body.u_char lum_dc_codelens[] = {        0, 1, 5, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0,};u_char lum_dc_symbols[] = {        0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,};u_char lum_ac_codelens[] = {        0, 2, 1, 3, 3, 2, 4, 3, 5, 5, 4, 4, 0, 0, 1, 0x7d,};u_char lum_ac_symbols[] = {        0x01, 0x02, 0x03, 0x00, 0x04, 0x11, 0x05, 0x12,        0x21, 0x31, 0x41, 0x06, 0x13, 0x51, 0x61, 0x07,        0x22, 0x71, 0x14, 0x32, 0x81, 0x91, 0xa1, 0x08,        0x23, 0x42, 0xb1, 0xc1, 0x15, 0x52, 0xd1, 0xf0,        0x24, 0x33, 0x62, 0x72, 0x82, 0x09, 0x0a, 0x16,        0x17, 0x18, 0x19, 0x1a, 0x25, 0x26, 0x27, 0x28,        0x29, 0x2a, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39,        0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49,        0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59,        0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69,        0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79,        0x7a, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89,        0x8a, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98,        0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,Berc, et. al.               Standards Track                    [Page 12]

RFC 2035           RTP Payload Format for JPEG Video        October 1996        0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6,        0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3, 0xc4, 0xc5,        0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2, 0xd3, 0xd4,        0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda, 0xe1, 0xe2,        0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9, 0xea,        0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8,        0xf9, 0xfa,};u_char chm_dc_codelens[] = {        0, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0,};u_char chm_dc_symbols[] = {        0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,};u_char chm_ac_codelens[] = {        0, 2, 1, 2, 4, 4, 3, 4, 7, 5, 4, 4, 0, 1, 2, 0x77,};u_char chm_ac_symbols[] = {        0x00, 0x01, 0x02, 0x03, 0x11, 0x04, 0x05, 0x21,        0x31, 0x06, 0x12, 0x41, 0x51, 0x07, 0x61, 0x71,        0x13, 0x22, 0x32, 0x81, 0x08, 0x14, 0x42, 0x91,        0xa1, 0xb1, 0xc1, 0x09, 0x23, 0x33, 0x52, 0xf0,        0x15, 0x62, 0x72, 0xd1, 0x0a, 0x16, 0x24, 0x34,        0xe1, 0x25, 0xf1, 0x17, 0x18, 0x19, 0x1a, 0x26,        0x27, 0x28, 0x29, 0x2a, 0x35, 0x36, 0x37, 0x38,        0x39, 0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48,        0x49, 0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58,        0x59, 0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,        0x69, 0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78,        0x79, 0x7a, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,        0x88, 0x89, 0x8a, 0x92, 0x93, 0x94, 0x95, 0x96,        0x97, 0x98, 0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5,        0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4,        0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3,        0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2,        0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda,        0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9,        0xea, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8,        0xf9, 0xfa,};u_char *MakeQuantHeader(u_char *p, u_char *qt, int tableNo){Berc, et. al.               Standards Track                    [Page 13]

RFC 2035           RTP Payload Format for JPEG Video        October 1996        *p++ = 0xff;        *p++ = 0xdb;            /* DQT */        *p++ = 0;               /* length msb */        *p++ = 67;              /* length lsb */        *p++ = tableNo;        memcpy(p, qt, 64);        return (p + 64);}u_char *MakeHuffmanHeader(u_char *p, u_char *codelens, int ncodes, u_char *symbols,                  int nsymbols, int tableNo, int tableClass){        *p++ = 0xff;        *p++ = 0xc4;            /* DHT */        *p++ = 0;               /* length msb */        *p++ = 3 + ncodes + nsymbols; /* length lsb */        *p++ = tableClass << 4 | tableNo;        memcpy(p, codelens, ncodes);        p += ncodes;        memcpy(p, symbols, nsymbols);        p += nsymbols;        return (p);}/* * Given an RTP/JPEG type code, q factor, width, and height, * generate a frame and scan headers that can be prepended * to the RTP/JPEG data payload to produce a JPEG compressed * image in interchange format (except for possible trailing * garbage and absence of an EOI marker to terminate the scan). */int MakeHeaders(u_char *p, int type, int q, int w, int h){        u_char *start = p;        u_char lqt[64];        u_char cqt[64];        /* convert from blocks to pixels */        w <<= 3;        h <<= 3;        MakeTables(q, lqt, cqt);        *p++ = 0xff;        *p++ = 0xd8;            /* SOI */        p = MakeQuantHeader(p, lqt, 0);Berc, et. al.               Standards Track                    [Page 14]

RFC 2035           RTP Payload Format for JPEG Video        October 1996        p = MakeQuantHeader(p, cqt, 1);        p = MakeHuffmanHeader(p, lum_dc_codelens,                              sizeof(lum_dc_codelens),                              lum_dc_symbols,                              sizeof(lum_dc_symbols), 0, 0);        p = MakeHuffmanHeader(p, lum_ac_codelens,                              sizeof(lum_ac_codelens),                              lum_ac_symbols,                              sizeof(lum_ac_symbols), 0, 1);        p = MakeHuffmanHeader(p, chm_dc_codelens,                              sizeof(chm_dc_codelens),                              chm_dc_symbols,                              sizeof(chm_dc_symbols), 1, 0);        p = MakeHuffmanHeader(p, chm_ac_codelens,                              sizeof(chm_ac_codelens),                              chm_ac_symbols,                              sizeof(chm_ac_symbols), 1, 1);        *p++ = 0xff;        *p++ = 0xc0;            /* SOF */        *p++ = 0;               /* length msb */        *p++ = 17;              /* length lsb */        *p++ = 8;               /* 8-bit precision */        *p++ = h >> 8;          /* height msb */        *p++ = h;               /* height lsb */        *p++ = w >> 8;          /* width msb */        *p++ = w;               /* wudth lsb */        *p++ = 3;               /* number of components */        *p++ = 0;               /* comp 0 */        if (type == 0)                *p++ = 0x21;    /* hsamp = 2, vsamp = 1 */        else                *p++ = 0x22;    /* hsamp = 2, vsamp = 2 */        *p++ = 0;               /* quant table 0 */        *p++ = 1;               /* comp 1 */        *p++ = 0x11;            /* hsamp = 1, vsamp = 1 */        *p++ = 1;               /* quant table 1 */        *p++ = 2;               /* comp 2 */        *p++ = 0x11;            /* hsamp = 1, vsamp = 1 */        *p++ = 1;               /* quant table 1 */        *p++ = 0xff;        *p++ = 0xda;            /* SOS */        *p++ = 0;               /* length msb */        *p++ = 12;              /* length lsb */        *p++ = 3;               /* 3 components */        *p++ = 0;               /* comp 0 */Berc, et. al.               Standards Track                    [Page 15]

RFC 2035           RTP Payload Format for JPEG Video        October 1996        *p++ = 0;               /* huffman table 0 */        *p++ = 1;               /* comp 1 */        *p++ = 0x11;            /* huffman table 1 */        *p++ = 2;               /* comp 2 */        *p++ = 0x11;            /* huffman table 1 */        *p++ = 0;               /* first DCT coeff */        *p++ = 63;              /* last DCT coeff */        *p++ = 0;               /* sucessive approx. */        return (p - start);};Berc, et. al.               Standards Track                    [Page 16]