H261 AND H263-BASED PROGRAMABLE VIDEO TRANSCEIVERS

The video quality versus bitrate performance of the ~~aw HmYH u ~~KXH.%~~ H.261 and H.268codecs is characterised and a bitrate I control algorithm is proposed in order to maintain a selectable near-constant video bitrate. The source codecs are operated at four different bitrates, which result in a constant symbol rate after error correcI tion coding. This system constellation allowed us to 1 maintain a constant video user bandwidth require- +-q-kw ,"%, ~~a~~~l~~~l ment, but benefit from improving channel conditions in terms of better video quality, when invoking more bandwidth efficient modem schemes ranging from 1 to 6 bits per symbol.