2.2.2 RTVideo Basic RTP Payload Format
The size of the RTVideo Basic Payload Format header varies. The minimum size is one byte without the codec headers present. If the codec headers are present, the maximum size is 65 bytes.
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A - M (1 bit): Payload format mode. This field MUST be set to zero in the RTVideo Basic RTP Payload Format mode. The field is set to one in other RTP payload formats, as specified in sections 2.2.3, 2.2.4, and 2.2.5.
B - C (1 bit): Cached frame flag. A value of one specifies a cached frame. A value of zero specifies the frame is not a cached frame.
C - SP (1 bit): Super P-frame (SP-frame) flag. A value of one specifies an SP-frame. A value of zero specifies the frame is not an SP-frame.
D - L (1 bit): Last packet flag. Indicates whether this packet is the last packet of the video frame, excluding FEC metadata packets. A value of one specifies the last packet. A value of zero specifies it is not the last packet.
E - O (1 bit): MUST be set to one.
F - I (1 bit): I-frame flag. Indicates whether the frame is an I-frame. A value of one indicates the frame is an I-frame. A value of zero indicates that the frame is not an I-frame, but rather a SP-frame, P-frame, or B-frame.
G - S (1 bit): Codec headers presence flag. Indicates presence of the codec headers. A value of one indicates the Codec Headers Length field is present. A value of zero indicates the Codec Headers Length field is not present.
H - F (1 bit): First packet flag. Indicates whether the packet is the first packet of the video frame, excluding FEC metadata packets. A value of one indicates the packet is the first packet. A value of zero indicates it is not the first packet.
I - Codec Headers Length (1 byte, optional): The size of Codec Headers Bytes field. Only present when the S bit is one. The value of this field MUST be less than or equal to 63.
Codec Headers Bytes (variable): Codec headers (binding byte, sequence header and entry point header). Only present when the S bit is one and the Codec Headers Length is greater than zero. The size is indicated by the Codec Headers Length field.
Codec headers include the binding byte, the sequence header, and the entry point header. The sequence header and the entry point header are specified in [SMPTE-VC-1].
The binding byte is the first byte of the codecs headers bytes. It indicates whether B-frames are present in the bitstream. Only two values are defined: 0x25 and 0x27. A binding byte of 0x25 indicates B-frames are present. A binding byte of 0x27 indicates B-frames are not present.
The entry point header SHOULD be carried at the beginning of the video payload data. When present, the entry point header carried in the video payload data supersedes the entry point header carried in the Codec Headers Bytes field of the payload format header.<2>