Low Delay Mode
MPEG provides for a low delay mode by setting certain parameters. For low delay, the total buffer delay must be minimized. The low delay mode is signalled with a flag, low_delay, in the sequence header.
B pictures are not used in this mode. In addition, dual-prime prediction may be used in P pictures to improve their quality for the available bit rate. Use of intra coded slices instead of complete intra coded pictures also reduces the required buffer occupancy and delay.
Low delay mode also explicitly allows the encoder to use occasionally a larger access unit for a picture, and skip some succeeding pictures. The picture using the large number of bits is called a large picture, and is repeated at the receiver display to replace the skipped pictures. For use by the VBV model, this is indicated by a discontinuity in the value of temporal_reference for the next picture. This value need not be noted by a decoder whose buffer management is based on time stamps, which can infer the required repetitions and/or explicitly read the required information from the values of repeat_first_field and top_field_first.