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rfc:rfc2035

Network Working Group L. Berc Request for Comments: 2035 Digital Equipment Corporation Category: Standards Track W. Fenner

                                                            Xerox PARC
                                                          R. Frederick
                                                            Xerox PARC
                                                            S. McCanne
                                          Lawrence Berkeley Laboratory
                                                          October 1996
            RTP Payload Format for JPEG-compressed Video

Status 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 represented

Berc, 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 even

Berc, 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 1996

3.1. 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 1996

3.1.7. 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. Discussion

4.1. 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 in Appendix 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 1996

4.3. 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.gov

Berc, et. al. Standards Track [Page 9] RFC 2035 RTP Payload Format for JPEG Video October 1996

7. 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 in
   ftp://ftp.uu.net/graphics/jpeg/jfif.ps.gz.

[5] Tom Lane et. al., The Independent JPEG Group software JPEG codec.

   Source code available in
   ftp://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 1996

Appendix 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 */ void MakeTables(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]

/data/webs/external/dokuwiki/data/pages/rfc/rfc2035.txt · Last modified: 1996/10/31 00:05 by 127.0.0.1

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