| 摘要 |
Reverse playback of MPEG video from a random access source takes advantage of the symmetry of B frames within an IB data stream. The IB data stream is processed by a parsing algorithm to identify within the B frames during playback those bits associated with motion vector identification and values to develop a parsed B frame table. When the IB data stream is output from the storage source for reverse playback, the IB data stream is rearranged into a reversed IB data stream. As each B frame is processed prior to input to an MPEG decoder, the parsed B frame table is used to manipulate the appropriate bits within the B frames to turn forward motion vectors into backward motion vectors, and vice versa. Then when the B frame is decoded by the MPEG decoder the respective motion vectors are associated with the appropriate I frames within the reversed IB data stream to produce accurate decoding of the B frames during reverse playback. Alternatively the MPEG decoder controller may be modified to provide both forward and reverse playback capabilities by reversing the stores within a prediction module 22 of the MPEG decoder so that for reverse playback the first I frame in the reversed IB data stream is input to a fixture store 26 rather than a prior store 24 and the next I frame is input to the prior store 24 rather than the future store 21. Again the B frame motion vectors in this manner are associated with the proper I frames for decoding. |
