How do MPEG and H.261 differ ?
H.261 was targeted for teleconferencing applications where motion is naturally more limited. Motion vectors are restricted to a range of +/- 15 pixels. Accuracy is reduced since H.261 motion vectors are restricted to integer-pel accuracy. Other syntactic differences include: no B-pictures, different quantization method. H.261 is also known as P*64. P is an integer number meant to represent multiples of 64kbit/sec. In the end, this nomenclature probably won’t be used as many services other than video will adopt the philosophy of arbitrary B channel (64kbit) bitrate scalability.
A. H.261, also known as Px64, was targeted for teleconferencing applications where motion is naturally more limited. Motion vectors are restricted to a range of +/- 15 pixel unit displacements. Prediction accuracy is reduced since H.261 motion vectors are specified to only integer-pel accuracy. Other quality syntactic differences include: no B-pictures, inferior mismatch control.
