2.2.2.3 RTP Header Usage for RTP FEC Data

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The syntax of the RTP header is specified in [RFC3550] section 5.1. The fields of the fixed RTP header have their usual meaning, as specified in [RFC3550] section 5.1 and by the RTP profile in use, with the following additional notes:

Marker (M): This bit MUST be set to 1.

Payload Type (PT): There is no predefined RTP payload type number for this RTP payload format. Instead, this 7-bit field MUST be assigned to a number that is established through some mechanism outside of RTP. For example, it can be assigned by using the SDP, as specified in section 2.2.5.

Timestamp: This 32-bit field MUST be set to the value of the Timestamp field of the last source RTP packet in the span of source RTP packets that is encoded into this FEC RTP packet. The value of the Timestamp field is expressed by using the same time units used for the Timestamp field of the source RTP packets, unless otherwise specified (for example, through SDP).