A decoder receives frames of data that have been block coded, then convolutionally coded, at a rate of multiple frames per block. As each frame is received, the decoder counts it, stores convolutional code path information, and updates metric values pertaining to the paths. Once per block of frames, the decoder selects a path having the best metric value, convolutionally decodes one block, detects errors from both the block code and path metric, and generates error information. From the error information, the decoder decides whether block synchronization has been acquired or lost, and clears, decrements, or sets the frame count accordingly. If synchronized, the decoder outputs the block and its error information, and updates the path memory in preparation to decode the next block. Otherwise, the decoder prepares to reacquire block synchronization.