rfc3551.txt

完整的RTP RTSP代码库

   The transmitted parameters of a G.729/G.729A 10-ms frame, consisting
   of 80 bits, are defined in Recommendation G.729, Table 8/G.729.  The
   mapping of the these parameters is given below in Fig. 4.  The
   diagrams show the bit packing in "network byte order", also known as
   big-endian order.  The bits of each 32-bit word are numbered 0 to 31,
   with the most significant bit on the left and numbered 0.  The octets
   (bytes) of each word are transmitted most significant octet first.
   The bits of each data field are numbered in the order as produced by
   the G.729 C code reference implementation.

   The packing of the G.729 Annex B comfort noise frame is shown in Fig.
   5.

          0                   1
          0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |L|  LSF1   |  LSF2 |   GAIN  |R|
         |S|         |       |         |E|
         |F|         |       |         |S|
         |0|0 1 2 3 4|0 1 2 3|0 1 2 3 4|V|    RESV = Reserved (zero)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 5: G.729 Annex B bit packing






Schulzrinne & Casner        Standards Track                    [Page 21]

RFC 3551                    RTP A/V Profile                    July 2003


4.5.7 G729D and G729E

   Annexes D and E to ITU-T Recommendation G.729 provide additional data
   rates.  Because the data rate is not signaled in the bitstream, the
   different data rates are given distinct RTP encoding names which are
   mapped to distinct payload type numbers.  G729D indicates a 6.4
   kbit/s coding mode (G.729 Annex D, for momentary reduction in channel
   capacity), while G729E indicates an 11.8 kbit/s mode (G.729 Annex E,
   for improved performance with a wide range of narrow-band input
   signals, e.g., music and background noise).  Annex E has two
   operating modes, backward adaptive and forward adaptive, which are
   signaled by the first two bits in each frame (the most significant
   two bits of the first octet).

   The voice activity detector (VAD) and comfort noise generator (CNG)
   algorithm specified in Annex B of G.729 may be used with Annex D and
   Annex E frames in addition to G.729 and G.729 Annex A frames.  The
   algorithm details for the operation of Annexes D and E with the Annex
   B CNG are specified in G.729 Annexes F and G.  Note that Annexes F
   and G do not introduce any new encodings.  Receivers MUST accept
   comfort noise frames if restriction of their use has not been
   signaled.  The MIME registrations for G729D and G729E in RFC 3555 [7]
   specify a parameter that MAY be used with MIME or SDP to restrict the
   use of comfort noise frames.

   For G729D, an RTP packet may consist of zero or more G.729 Annex D
   frames, followed by zero or one G.729 Annex B frame.  Similarly, for
   G729E, an RTP packet may consist of zero or more G.729 Annex E
   frames, followed by zero or one G.729 Annex B frame.  The presence of
   a comfort noise frame can be deduced from the length of the RTP
   payload.

   A single RTP packet must contain frames of only one data rate,
   optionally followed by one comfort noise frame.  The data rate may be
   changed from packet to packet by changing the payload type number.
   G.729 Annexes D, E and H describe what the encoding and decoding
   algorithms must do to accommodate a change in data rate.

   For G729D, the bits of a G.729 Annex D frame are formatted as shown
   below in Fig. 6 (cf.  Table D.1/G.729).  The frame length is 64 bits.











Schulzrinne & Casner        Standards Track                    [Page 22]

RFC 3551                    RTP A/V Profile                    July 2003


       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |L|      L1     |    L2   |    L3   |        P1     |     C1    |
      |0|             |         |         |               |           |
      | |0 1 2 3 4 5 6|0 1 2 3 4|0 1 2 3 4|0 1 2 3 4 5 6 7|0 1 2 3 4 5|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | C1  |S1 | GA1 | GB1 |  P2   |        C2       |S2 | GA2 | GB2 |
      |     |   |     |     |       |                 |   |     |     |
      |6 7 8|0 1|0 1 2|0 1 2|0 1 2 3|0 1 2 3 4 5 6 7 8|0 1|0 1 2|0 1 2|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 6: G.729 Annex D bit packing

   The net bit rate for the G.729 Annex E algorithm is 11.8 kbit/s and a
   total of 118 bits are used.  Two bits are appended as "don't care"
   bits to complete an integer number of octets for the frame.  For
   G729E, the bits of a data frame are formatted as shown in the next
   two diagrams (cf. Table E.1/G.729).  The fields for the G729E forward
   adaptive mode are packed as shown in Fig. 7.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0 0|L|      L1     |    L2   |    L3   |        P1     |P| C0_1|
      |   |0|             |         |         |               |0|     |
      |   | |0 1 2 3 4 5 6|0 1 2 3 4|0 1 2 3 4|0 1 2 3 4 5 6 7| |0 1 2|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       |   C1_1      |     C2_1    |   C3_1      |    C4_1     |
      |       |             |             |             |             |
      |3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | GA1 |  GB1  |    P2   |   C0_2      |     C1_2    |   C2_2    |
      |     |       |         |             |             |           |
      |0 1 2|0 1 2 3|0 1 2 3 4|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | |    C3_2     |     C4_2    | GA2 | GB2   |DC |
      | |             |             |     |       |   |
      |6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2|0 1 2 3|0 1|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 7: G.729 Annex E (forward adaptive mode) bit packing

   The fields for the G729E backward adaptive mode are packed as shown
   in Fig. 8.






Schulzrinne & Casner        Standards Track                    [Page 23]

RFC 3551                    RTP A/V Profile                    July 2003


       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |1 1|       P1      |P|       C0_1              |     C1_1      |
      |   |               |0|                    1 1 1|               |
      |   |0 1 2 3 4 5 6 7|0|0 1 2 3 4 5 6 7 8 9 0 1 2|0 1 2 3 4 5 6 7|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   |  C2_1       | C3_1        | C4_1        |GA1  | GB1   |P2 |
      |   |             |             |             |     |       |   |
      |8 9|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2|0 1 2 3|0 1|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     |          C0_2           |       C1_2        |    C2_2   |
      |     |                    1 1 1|                   |           |
      |2 3 4|0 1 2 3 4 5 6 7 8 9 0 1 2|0 1 2 3 4 5 6 7 8 9|0 1 2 3 4 5|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | |    C3_2     |     C4_2    | GA2 | GB2   |DC |
      | |             |             |     |       |   |
      |6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2|0 1 2 3|0 1|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 8: G.729 Annex E (backward adaptive mode) bit packing

4.5.8 GSM

   GSM (Group Speciale Mobile) denotes the European GSM 06.10 standard
   for full-rate speech transcoding, ETS 300 961, which is based on
   RPE/LTP (residual pulse excitation/long term prediction) coding at a
   rate of 13 kb/s [11,12,13].  The text of the standard can be obtained
   from:

   ETSI (European Telecommunications Standards Institute)
   ETSI Secretariat: B.P.152
   F-06561 Valbonne Cedex
   France
   Phone: [phone]
   Fax:   [phone]

   Blocks of 160 audio samples are compressed into 33 octets, for an
   effective data rate of 13,200 b/s.

4.5.8.1  General Packaging Issues

   The GSM standard (ETS 300 961) specifies the bit stream produced by
   the codec, but does not specify how these bits should be packed for
   transmission.  The packetization specified here has subsequently been
   adopted in ETSI Technical Specification TS 101 318.  Some software
   implementations of the GSM codec use a different packing than that
   specified here.



Schulzrinne & Casner        Standards Track                    [Page 24]

RFC 3551                    RTP A/V Profile                    July 2003


               field  field name  bits  field  field name  bits
               ________________________________________________
               1      LARc[0]     6     39     xmc[22]     3
               2      LARc[1]     6     40     xmc[23]     3
               3      LARc[2]     5     41     xmc[24]     3
               4      LARc[3]     5     42     xmc[25]     3
               5      LARc[4]     4     43     Nc[2]       7
               6      LARc[5]     4     44     bc[2]       2
               7      LARc[6]     3     45     Mc[2]       2
               8      LARc[7]     3     46     xmaxc[2]    6
               9      Nc[0]       7     47     xmc[26]     3
               10     bc[0]       2     48     xmc[27]     3
               11     Mc[0]       2     49     xmc[28]     3
               12     xmaxc[0]    6     50     xmc[29]     3
               13     xmc[0]      3     51     xmc[30]     3
               14     xmc[1]      3     52     xmc[31]     3
               15     xmc[2]      3     53     xmc[32]     3
               16     xmc[3]      3     54     xmc[33]     3
               17     xmc[4]      3     55     xmc[34]     3
               18     xmc[5]      3     56     xmc[35]     3
               19     xmc[6]      3     57     xmc[36]     3
               20     xmc[7]      3     58     xmc[37]     3
               21     xmc[8]      3     59     xmc[38]     3
               22     xmc[9]      3     60     Nc[3]       7
               23     xmc[10]     3     61     bc[3]       2
               24     xmc[11]     3     62     Mc[3]       2
               25     xmc[12]     3     63     xmaxc[3]    6
               26     Nc[1]       7     64     xmc[39]     3
               27     bc[1]       2     65     xmc[40]     3
               28     Mc[1]       2     66     xmc[41]     3
               29     xmaxc[1]    6     67     xmc[42]     3
               30     xmc[13]     3     68     xmc[43]     3
               31     xmc[14]     3     69     xmc[44]     3
               32     xmc[15]     3     70     xmc[45]     3
               33     xmc[16]     3     71     xmc[46]     3
               34     xmc[17]     3     72     xmc[47]     3
               35     xmc[18]     3     73     xmc[48]     3
               36     xmc[19]     3     74     xmc[49]     3
               37     xmc[20]     3     75     xmc[50]     3
               38     xmc[21]     3     76     xmc[51]     3

                      Table 2: Ordering of GSM variables









Schulzrinne & Casner        Standards Track                    [Page 25]

RFC 3551                    RTP A/V Profile                    July 2003


   Octet  Bit 0   Bit 1   Bit 2   Bit 3   Bit 4   Bit 5   Bit 6   Bit 7
   _____________________________________________________________________
       0    1       1       0       1    LARc0.0 LARc0.1 LARc0.2 LARc0.3
       1 LARc0.4 LARc0.5 LARc1.0 LARc1.1 LARc1.2 LARc1.3 LARc1.4 LARc1.5
       2 LARc2.0 LARc2.1 LARc2.2 LARc2.3 LARc2.4 LARc3.0 LARc3.1 LARc3.2
       3 LARc3.3 LARc3.4 LARc4.0 LARc4.1 LARc4.2 LARc4.3 LARc5.0 LARc5.1
       4 LARc5.2 LARc5.3 LARc6.0 LARc6.1 LARc6.2 LARc7.0 LARc7.1 LARc7.2
       5  Nc0.0   Nc0.1   Nc0.2   Nc0.3   Nc0.4   Nc0.5   Nc0.6  bc0.0
       6  bc0.1   Mc0.0   Mc0.1  xmaxc00 xmaxc01 xmaxc02 xmaxc03 xmaxc04
       7 xmaxc05 xmc0.0  xmc0.1  xmc0.2  xmc1.0  xmc1.1  xmc1.2  xmc2.0
       8 xmc2.1  xmc2.2  xmc3.0  xmc3.1  xmc3.2  xmc4.0  xmc4.1  xmc4.2
       9 xmc5.0  xmc5.1  xmc5.2  xmc6.0  xmc6.1  xmc6.2  xmc7.0  xmc7.1
      10 xmc7.2  xmc8.0  xmc8.1  xmc8.2  xmc9.0  xmc9.1  xmc9.2  xmc10.0
      11 xmc10.1 xmc10.2 xmc11.0 xmc11.1 xmc11.2 xmc12.0 xmc12.1 xcm12.2
      12  Nc1.0   Nc1.1   Nc1.2   Nc1.3   Nc1.4   Nc1.5   Nc1.6   bc1.0
      13  bc1.1   Mc1.0   Mc1.1  xmaxc10 xmaxc11 xmaxc12 xmaxc13 xmaxc14
      14 xmax15  xmc13.0 xmc13.1 xmc13.2 xmc14.0 xmc14.1 xmc14.2 xmc15.0
      15 xmc15.1 xmc15.2 xmc16.0 xmc16.1 xmc16.2 xmc17.0 xmc17.1 xmc17.2
      16 xmc18.0 xmc18.1 xmc18.2 xmc19.0 xmc19.1 xmc19.2 xmc20.0 xmc20.1
      17 xmc20.2 xmc21.0 xmc21.1 xmc21.2 xmc22.0 xmc22.1 xmc22.2 xmc23.0
      18 xmc23.1 xmc23.2 xmc24.0 xmc24.1 xmc24.2 xmc25.0 xmc25.1 xmc25.2
      19  Nc2.0   Nc2.1   Nc2.2   Nc2.3   Nc2.4   Nc2.5   Nc2.6   bc2.0
      20  bc2.1   Mc2.0   Mc2.1  xmaxc20 xmaxc21 xmaxc22 xmaxc23 xmaxc24
      21 xmaxc25 xmc26.0 xmc26.1 xmc26.2 xmc27.0 xmc27.1 xmc27.2 xmc28.0
      22 xmc28.1 xmc28.