Method and apparatus for video frame selection for improved coding quality at low bit-rates

Abstract

A method and apparatus for advantageously selecting video frames to be coded in order to improve the coding quality of a low bit-rate coder. In particular, temporal sub-sampling (i.e., selecting a set of frames to be coded from the complete incoming sequence of frames) is performed so that the frames which are to be coded are advantageously selected based upon a coding criterion, such as, for example, prediction gain (i.e., reduction in DFD variance). Specifically, in one illustrative embodiment, a larger number of frames are advantageously selected during periods of fast change, and correspondingly fewer frames are selected during other periods, while thereby keeping the overall apparent frame-rate fixed. The fixed frame-rate may, for example, be maintained by grouping the incoming sequence of frames into sequential groups of M consecutive frames, and then selecting exactly one frame per every M input frames, while permitting the selected frame to be at any advantageously selected location within the group of M frames. Thus, non-uniform frame selection is achieved, even though exactly one frame is actually coded within each superframe. Moreover, by basing the specific frame selection on an appropriate coding criterion (e.g., prediction gain), a substantial improvement in coder performance may be achieved for those critical portions of the video sequence during which a conventional coder's performance may be drastically reduced, without changing the apparent frame-rate.