Nokia 9290 Video Style Guide - Page 7

Nokia Mobile Phones Nokia 9290 Communicator Video Editing for the Nokia 9290 Communicator 7(12) call. The data rate of the call can vary from 9.6 kbps to 43.2 kbps depending on the network capabilities and conditions. You can also download NIM files to your computer via a wired Internet connection, such as a landline modem connection. Then, you can copy the files to your communicator using PC Suite for Nokia 9290 Communicator. Note: You cannot stream NIM files to the Nokia 9290 Communicator. Streaming refers to simultaneous downloading and playback. 4.2 Transferring Video Clips from a PC to the Nokia 9290 Communicator You can use PC Suite for Nokia 9290 Communicator to copy NIM files to your communicator. For more information, see the 'Your communicator on your PC's desktop' section in the Nokia 9290 Communicator User guide. 5. Appendix A. Audio-Visual Compression for the Nokia 9290 Communicator 5.1 Basics of Video Coding A video sequence consists of a series of still images. Video compression methods are based on reducing the redundant and perceptually irrelevant parts of video sequences. The redundancy in video sequences can be categorised into spatial, temporal and spectral redundancy. Spatial redundancy means the correlation between neighboring pixels. Temporal redundancy means that the same objects appearing in the previous image are likely to appear in the current image as well. Compression can be achieved by generating motion compensation data, which describes the motion between the current and the previous image. It can be said that the current image is predicted from the previous one. Spectral redundancy means the correlation between the different colour components of the same image. However, efficient enough compression cannot usually be reached by just reducing the redundancy of the sequence. Thus, video encoders must also discard some non-redundant information. When doing this, the encoders take into account the properties of the human visual system and mainly discard such information which is least important for the subjective quality of the image. In addition, the redundancy of the encoded bit-stream is reduced by means of efficient lossless coding of compression parameters and coefficients. The main technique is to use variable length codes. Video compression methods typically differentiate images that can or cannot utilise temporal redundancy reduction. Compressed images, which do not utilise temporal redundancy reduction methods, are usually called INTRA or Iframes whereas temporally predicted images are called INTER or P-frames. In the INTER frame case, the predicted (motion-compensated) image is rarely precise enough, and therefore a spatially compressed prediction error image is also associated with each INTER frame. In video coding, there is always a trade-off between bit rate and quality. Some image sequences may be harder to compress than others due to rapid motion or complex texture, for example. In order to meet a constant bit rate target, the video encoder controls the frame rate as well as the quality of the images: the more difficult the image is to compress, the worse the image quality is. If variable bit rate is allowed, the encoder can maintain a constant video quality. ITU-T H.263 video codec utilises the discrete cosine transform (DCT) to reduce spatial redundancy. The transform converts a block of pixels to coefficients that represent the spatial frequency components of the block. Only the frequencies appearing in the block have high-amplitude coefficient values and other coefficients are close to zero. For example, a constantly coloured block has only one spatial frequency and it is transformed to one non-zero DCT Copyright  Nokia Corporation 2001-2002. All rights reserved.