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Hầu hết các trình duyệt web không hỗ trợ các accesskeys chữ cái và cách gõ chữ là rất dễ dàng. Thiết kế này phần lớn là vì đơn giản: sắp xếp lại các chữ cái cho ngay cả phân phối kết quả cho một số lượng nhỏ các thiết bị có nghĩa rằng mỗi thiết bị và danh sách kết quả sẽ khác nhau, làm giảm cả trong thiết bị và khả năng dự báo qua thiết bị. | 144 GRAPHIC AND MEDIA DESIGN despite the MPEG-4 standard most networks do not yet allow you to detect network conditions and respond accordingly. Most networks deliver video content in individual full-screen refreshes. Achieving the minimally acceptable frame rate is more difficult in this environment. If the media delivery system is using the MPEG-4 capabilities of partial-screen refreshes you will get higher perceived frame rates. MPEG-4 compression of motion pictures involves reducing the amount of information that is needed to describe a series of frames by sending full information only once every several frames and using techniques to predict the other frames and describe only the changes from the anchor frame key frame . Predicted frames follow and contain much less information than the key frame. The ratio of predicted to key frames should not exceed ten to one. A variation on this technique is useful for creating animations. The human eye will fill in details that do not actually exist so the designer can merely hint at those details using less memory. Lossless encoding will give slightly better quality than lossy encoding but between lost frames low bandwidth and limited device processor and speaker capabilities users are unlikely to notice. In exchange lossy encoding gives better compression which improves the user experience. You may find that lossy encoding allows you to encode at a higher frequency. As is true with any video process professional level practices will improve end quality. These include using professional-grade encoding hardware such as SDI or Firewire and converting from analogue to digital signal at most once. Your standard process will likely cover all these issues. 7.3 SOUND Customer testing indicates that low-resolution low-frame-rate images are perceived as better when accompanied by better quality audio. Thus audio quality has a disproportionate effect on the overall user experience. Fortunately most PCDs are optimized for .
