| 摘要 |
The presently preferred methods of the present invention take advantage of the syntax structure of H.264 and adaptively switch the entropy coding mode between CABAC and CAVLC. In those profiles of H.264 where CABAC is supported such as the Main profile and the High profiles (HP, Hi10, Hi422, Hi444), the entropy coding mode to be used is specified via a picture parameter set ("PPS"), where a particular PPS is specified for each slice in its header ("slice header"). The encoders of the present invention provide a multiple-PPS for both the CAVLC and CABAC, so that bitstreams are produced by both CAVLC and CABAC. CAVLC, having a simpler algorithm structure, is implemented as a part of the video pipe, where each single video pipe stage is designed to operate within a pre-defined number of clock cycles. The video pipe generates SE at pre-scheduled instances buffered in FIFO. The SE serves as input to CABAC, where CABAC encodes the SE in an event-driven fashion. During this process, CABAC is monitored to determine if the CABAC engine is able to keep up with the video pipe. The video pipe, implemented using CAVLC, by design will complete the encoding process within the allotted time. However, CABAC, although having better encoding efficiency and where its generated output is more desirable, its encoding completion time is uncertain and may require more time than it is allowed. Thus if CABAC cannot complete the encoding process within the allotted time, the bitstream generated by CABAC would not be complete and it cannot be used. If CABAC can complete the encoding process within the allotted time, the CABAC engine would be allowed to complete the encoding process and its generated output would be used as the bitstream of choice.
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