TABLE OF CONTENTS One of the initial aims in the design of a new low bit rate video codec was to replace H.261 with a more efficient one, that took the name of H.263. Hence the functionalities of H.261, but with some improvements, need to be included in this codec; they appear in Annex C of the H.263 specification that can be activated or disabled as desired [25-C]. Since this annex was introduced prior to all the other annexes, which later on were called optionalities, we introduce this annex prior to all the other options.
In H.263 the decoder can be instructed to alter its normal decoding mode and provide some extra display functions. Instructions for the alterations may be issued by an external device such as Recommendation H.245, which is a control protocol for multimedia communications [9]. Some of the commands and the actions are as follows.
This signal causes the decoder to freeze its displayed picture until a freeze release signal is received or a time-out period of at least six seconds has expired. A frozen picture is much better perceived by the viewer than, say, a broken picture due to channel errors, or if the encoder cannot deliver the compressed bit stream on time for a continuous display.
This command causes the encoder to encode its next picture in intra mode, with coding parameters to avoid buffer overflow. This mode in conjunction with the back channel reduces the probability...
