# N  Computation of b=AS for Video Codec |R12|p. 399

## N.1  Generalp. 399

If an MTSI client includes any video codecs in the SDP offer or answer, procedures to compute b=AS are left to the discretion of the implementation.

## N.2  Examplesp. 399

Table N.x shows example values of b=AS in IPv4 and IPv6 for each source bit-rate and image size pair of H.264/AVC. These values are determined from encoding a variety of content with the codec targeting a particular source bit-rate and then measuring the fluctuations of the encoded bit-rate in order to determine the recommended b=AS values. As the source bit-rate increases, the relative differences of b=AS values in IPv4 and IPv6 decrease as the proportion of RTP/UDP/IP headers in the packet decreases, but the required margin for the fluctuations increases. Different source bit-rates and b=AS values can be used for the same image size depending on service policy, alternative codec configurations, and the amount of bit-rate variation introduced by the rate control algorithm implementation.
Image size Source bit-rate b=AS (IPv4) b=AS (IPv6) Notes
176×144486466Maximum SDU size=1400 octets, average packet rate=14 packets/s, picture rate=7 pictures/s, average packets per picture=2 packets/picture, average header (RTP/UDP/IP) bit-rate=5/7 kbps (IPv4/IPv6)
320×240300384399Maximum SDU size=1400 octets, average packet rate=60 packets/s, picture rate=15 pictures/s, average packets per picture=4 packets/picture, average header (RTP/UDP/IP) bit-rate=20/32 kbps (IPv4/IPv6)
640×480512639653Maximum SDU size=1400 octets, average packet rate=60 packets/s, picture rate=15 pictures/s, average packets per picture=4 packets/picture, average header (RTP/UDP/IP) bit-rate=20/32 kbps (IPv4/IPv6)