1. A method of encoding a plurality of video frames having non-overlapping target blocks (macroblocks), the method comprising: encoding the plurality of video frames using importance maps, such that the importance maps modify quantization affecting the encoding quality of each target block to be encoded in each video frame, the importance maps being formed by: configuring the importance maps using temporal information and spatial information; and computationally causing the importance maps to indicate which parts of a video frame in the plurality of video frames are most noticeable to human perception, such that: (i) in blocks where the importance maps take on high values, the block quantization parameter (QP) is reduced relative to the frame quantization parameter QP frame , resulting in higher quality for those blocks, and (ii) in blocks where the importance maps take on low values, the block quantization parameter is increased relative to the frame quantization parameter QP frame , resulting in lower quality for those blocks; and (iii) each reduction or increase in block QP is represented in the importance map as a QP offset; wherein the spatial information for the importance maps is provided by a lookup table based on block variance, such lookup table indicating negative spatial QP offsets for block variances lower than 200 and positive spatial QP offsets for block variances above 400; and wherein the temporal information for the importance maps is provided by an algorithm that determines the encoding importance of each block for inter-prediction in future frames, where blocks of greater importance are assigned negative temporal QP offsets; and wherein the total QP offset for a given block is equal to the spatial QP offset plus the temporal QP offset, clipped to the maximum and minimum allowable QP values in the frame.