6. Payload Type Definitions
- Payload Type Definitions
Tables 4 and 5 define this profile's static payload type values for the PT field of the RTP data header. In addition, payload type values in the range 96-127 MAY be defined dynamically through a conference control protocol, which is beyond the scope of this document. For example, a session directory could specify that for a given session, payload type 96 indicates PCMU encoding, 8,000 Hz sampling rate, 2 channels. Entries in Tables 4 and 5 with payload type "dyn" have no static payload type assigned and are only used with a dynamic payload type. Payload type 2 was assigned to G721 in RFC 1890 and to its equivalent successor G726-32 in draft versions of this specification, but its use is now deprecated and that static payload type is marked reserved due to conflicting use for the payload formats G726-32 and AAL2-G726-32 (see Section 4.5.4). Payload type 13 indicates the Comfort Noise (CN) payload format specified in RFC 3389 [9]. Payload type 19 is marked "reserved" because some draft versions of this specification assigned that number to an earlier version of the comfort noise payload format. The payload type range 72-76 is marked "reserved" so that RTCP and RTP packets can be reliably distinguished (see Section "Summary of Protocol Constants" of the RTP protocol specification).
The payload types currently defined in this profile are assigned to exactly one of three categories or media types: audio only, video only and those combining audio and video. The media types are marked in Tables 4 and 5 as "A", "V" and "AV", respectively. Payload types of different media types SHALL NOT be interleaved or multiplexed within a single RTP session, but multiple RTP sessions MAY be used in parallel to send multiple media types. An RTP source MAY change payload types within the same media type during a session. See the section "Multiplexing RTP Sessions" of RFC 3550 for additional explanation.
PT encoding media type clock rate channels
name (Hz)
___________________________________________________
0 PCMU A 8,000 1
1 reserved A
2 reserved A
3 GSM A 8,000 1
4 G723 A 8,000 1
5 DVI4 A 8,000 1
6 DVI4 A 16,000 1
7 LPC A 8,000 1
8 PCMA A 8,000 1
9 G722 A 8,000 1
10 L16 A 44,100 2
11 L16 A 44,100 1
12 QCELP A 8,000 1
13 CN A 8,000 1
14 MPA A 90,000 (see text)
15 G728 A 8,000 1
16 DVI4 A 11,025 1
17 DVI4 A 22,050 1
18 G729 A 8,000 1
19 reserved A
20 unassigned A
21 unassigned A
22 unassigned A
23 unassigned A
dyn G726-40 A 8,000 1
dyn G726-32 A 8,000 1
dyn G726-24 A 8,000 1
dyn G726-16 A 8,000 1
dyn G729D A 8,000 1
dyn G729E A 8,000 1
dyn GSM-EFR A 8,000 1
dyn L8 A var. var.
dyn RED A (see text)
dyn VDVI A var. 1
Table 4: Payload types (PT) for audio encodings
PT encoding media type clock rate
name (Hz)
_____________________________________________
24 unassigned V
25 CelB V 90,000
26 JPEG V 90,000
27 unassigned V
28 nv V 90,000
29 unassigned V
30 unassigned V
31 H261 V 90,000
32 MPV V 90,000
33 MP2T AV 90,000
34 H263 V 90,000
35-71 unassigned ?
72-76 reserved N/A N/A
77-95 unassigned ?
96-127 dynamic ?
dyn H263-1998 V 90,000
Table 5: Payload types (PT) for video and combined
encodings
Session participants agree through mechanisms beyond the scope of this specification on the set of payload types allowed in a given session. This set MAY, for example, be defined by the capabilities of the applications used, negotiated by a conference control protocol or established by agreement between the human participants.
Audio applications operating under this profile SHOULD, at a minimum, be able to send and/or receive payload types 0 (PCMU) and 5 (DVI4). This allows interoperability without format negotiation and ensures successful negotiation with a conference control protocol.