Patent ID: 6912254

Claim:
A compressed data stream decoder comprising; an MPEG video decoder with plural compressed data streams coded in MPEG for decoding said plural compressed data streams and outputting decoded pictures and a frame memory for storing said decoded pictures; the frame memory having groups of frame memories, the number of frame memories being redundant rather than the types of pictures assigned to the compressed data streams, each of the groups of frame memories including a frame memory for storing a core picture decoded as the latest one, which is an I picture or P picture, a frame memory for storing a core picture decoded immediately before it, a frame memory for storing a B picture decoded as the latest one, and a frame memory for storing a picture unnecessary for a predictive coding; wherein, after starting the decoding, the MPEG video decoder changes the assignment to the frame memories in decoding use for the core picture from the storage of the latest core picture to the storage of the core picture decoded immediately before it, the frame memory for storing the core picture decoded immediately before it to the data storage of the picture unnecessary for the predictive coding, and the frame memory for storing the picture unnecessary for the predictive coding to the storage of the core picture decoded as the latest one, thereby storing a core picture to the frame memory for storing the core picture as the latest one and in decoding the B picture from the frame memory for storing the latest B picture to the storage of the picture unnecessary for the predictive coding for another picture and the frame memory for storing the picture unnecessary for the predictive coding for another picture unnecessary for the predictive coding for another picture to the storage of the latest B picture, thereby storing a latest B picture in the frame memory assigned to the latest B picture.