Techniques are described for efficient transcoding from a first format that supports I-units, P-units and B-units to a second format that supports I-units and P-units but does not support the B-units. In particular, techniques are described for converting B-frames or B-slices of the first format into P-frames or P-slices of the second format. The techniques avoid the need to decode and re-encode that frames or slices. Instead, residuals associated with the B-video blocks in the first format are augmented and made to be dependent upon only one of the two lists associated with the B-video blocks so that such B-video blocks in the first format can be redefined as P-video blocks in the second format.